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Thursday, 10 August 2017

The Condor, August 2017: Volume 119, Issue 3

The Condor: Ornithological Applications

Published by: American Ornithological Society















LINK

Table of Contents

Aug 2017 : Volume 119 Issue 3 

RESEARCH ARTICLES

Nest-site selection and nest survival of Bachman's Sparrows in two longleaf pine communities
Jason M. Winiarski, Alexander C. Fish, Christopher E. Moorman, John P. Carpenter, Christopher S. DePerno and Jessica M. Schillaci

Abstract

Longleaf pine (Pinus palustris) ecosystems of the southeastern United States have experienced high rates of habitat loss and fragmentation, coinciding with dramatic population declines of a variety of taxa that inhabit the system. The Bachman's Sparrow (Peucaea aestivalis), a species closely associated with fire-maintained longleaf pine communities, is listed as a species of conservation concern across its entire range. Bachman's Sparrow breeding biology may provide valuable insights into population declines and inform restoration and management of remnant longleaf pine forest, but the species' secretive nesting habits have received little attention. We located 132 Bachman's Sparrow nests in the Coastal Plain and Sandhills physiographic regions of North Carolina, USA, during 2014–2015, and modeled nest-site selection and nest survival as a function of vegetation characteristics, burn history, temporal factors, and landscape-level habitat amount. There were distinct differences in nest-site selection between regions, with Bachman's Sparrows in the Coastal Plain region selecting greater woody vegetation density and lower grass density at nest sites than at non-nest locations. In contrast, sparrows selected nest sites with intermediate grass density and higher tree basal area in the Sandhills region. Despite clear patterns of nest-site selection, we detected no predictors of nest survival in the Sandhills, and nest survival varied only with date in the Coastal Plain. Daily survival rates were similar between regions, and were consistent with published studies from the species' core range where declines are less severe. Overall, our results indicate that creating and maintaining community-specific vegetation characteristics through the application of frequent prescribed fire should increase the amount of nesting cover for Bachman's Sparrows.


California Spotted Owl (Strix occidentalis occidentalis) habitat use patterns in a burned landscape
Stephanie A. Eyes, Susan L. Roberts and Matthew D. Johnson

Abstract

Fire is a dynamic ecosystem process of mixed-conifer forests of the Sierra Nevada, but there is limited scientific information addressing wildlife habitat use in burned landscapes. Recent studies have presented contradictory information regarding the effects of stand-replacing wildfires on Spotted Owls (Strix occidentalis) and their habitat. While fire promotes heterogeneous forest landscapes shown to be favored by owls, high severity fire may create large canopy gaps that can fragment the closed-canopy habitat preferred by Spotted Owls. We used radio-telemetry to determine whether foraging California Spotted Owls (S. o. occidentalis) in Yosemite National Park, California, USA, showed selection for particular fire severity patch types within their home ranges. Our results suggested that Spotted Owls exhibited strong habitat selection within their home ranges for locations near the roost and edge habitats, and weak selection for lower fire severity patch types. Although owls selected high contrast edges with greater relative probabilities than low contrast edges, we did not detect a statistical difference between these probabilities. Protecting forests from stand-replacing fires via mechanical thinning or prescribed fire is a priority for management agencies, and our results suggest that fires of low to moderate severity can create habitat conditions within California Spotted Owls' home ranges that are favored for foraging.


Environmental conditions and animal behavior influence performance of solar-powered GPS-GSM transmitters
Michael E. Byrne, Amanda E. Holland, A. Lawrence Bryan and James C. Beasley

Abstract

Solar-powered GPS transmitters linked to the GSM cellular transmission system are a powerful new tool for avian research. Data collection can be researcher programmed or use dynamic fix (DF) rates that are automatically adjusted in accordance with battery charge. Lack of prior knowledge of fix (location) collection rates represents an obstacle to designing studies with transmitters that use DF rates. We assessed the quantity and quality of data collected by a commercially available DF transmitter. To assess fix collection rates, factors influencing fix collection rates, GPS accuracy, and the ability of transmitters to differentiate movement from nonmovement, we used a combination of controlled static tests at known locations, deployments on free-ranging Black Vultures (Coragyps atratus) and Turkey Vultures (Cathartes aura), and motion tests. During static testing, transmitters often collected upwards of 500 fixes per day in open habitats with little cloud cover. Hourly fix rates varied, commonly reaching 1 fix min−1 at midday but dropping to 1 fix hr−1 at night. The numbers of daylight fixes collected during vulture deployments were greater on days with little cloud cover, positively correlated with increasing daily movement rates, and positively correlated with available daylight hours, likely due in part to increased solar radiation near the summer solstice. Mean horizontal GPS error was 7.8 m (± 12.2 m SD). Mean vertical error was 4.5 m (± 142 m) above true elevation. Speed records >0 km hr−1 were reliable indicators of movement provided a 3D fix was obtained. Overall, the transmitters that we evaluated provided large volumes of data, but the inability to control data collection schedules may prove problematic for some applications. DF solar-powered transmitters appear best suited for use with active species in open habitats, and least suitable for use with species that inhabit high latitudes year-round or spend considerable time under forest cover.


Declining population trends of Hawaiian Petrel and Newell's Shearwater on the island of Kaua‘i, Hawaii, USA
André F. Raine, Nick D. Holmes, Marc Travers, Brian A. Cooper and Robert H. Day

Abstract

The island of Kaua‘i, Hawaii, USA, holds a large breeding populations of the endangered Hawaiian Petrel (Pterodroma sandwichensis) and a majority of the world population of the threatened Newell's Shearwater (Puffinus newelli). We evaluated island-wide population trends of both species. For Newell's Shearwaters, we considered radar counts at 13 sites between 1993 and 2013 and annual island-wide tallies of fledglings retrieved after being grounded by light attraction in 1979–2015 (Save Our Shearwaters [SOS] program). For Hawaiian Petrels, we considered radar counts alone. Radar data indicated a 78% decline overall in numbers of Hawaiian Petrels (at an average rate of ∼6% per year) and a 94% decline overall in numbers of Newell's Shearwaters (at an average rate of ∼13% per year) during the survey period. Most (92%) radar sites showed significant declines of Newell's Shearwaters across the entire survey period, as did 62% of sites for Hawaiian Petrels. The SOS recovery effort collected 30,522 Newell's Shearwater fledglings between 1979 and 2015. When we compared this dataset in pre- and post-Hurricane Iniki (September 1992) periods, we found a significant downward trend after Hurricane Iniki, similar to the trend seen in the radar data. The large-scale declines found in this study are not surprising, considering the significant threats facing both species on Kaua‘i, which include powerline collisions, light attraction, introduced predators, and habitat modification—threats which were potentially exacerbated after Hurricane Iniki. Improved conservation initiatives and an increased understanding of the various threats facing the 2 species are key to reversing these declines.


Effects of anthropogenic disturbance on bird diversity in Ethiopian montane forests
Addisu Asefa, Andrew B. Davies, Andrew E. McKechnie, Anouska A. Kinahan and Berndt J. van Rensburg

Abstract

The Afromontane forests of Ethiopia are global biodiversity hotspots, known for their high biological diversity and endemism. However, conservation of these areas is challenging due to increasing human threats, including encroachment of agriculture and settlements, overgrazing of livestock, and selective logging. We examined the effects of forest disturbances on birds, and highlights the potential conservation value of unprotected tropical montane forests for birds in the dry evergreen Afromontane forests of the Bale Mountains, Ethiopia. We sampled birds across 2 yr in both protected forests (characterized by low levels of cultivation, overgrazing, and logging) and unprotected forests (higher levels of disturbance). Using functional traits of birds related to habitat type, diet, and foraging stratum, we characterized the differences between protected and unprotected forests in terms of avian species richness, abundance, and assemblage composition. Overall, species richness was 27% higher and bird abundance was 19% higher in unprotected forests. In contrast, species richness and abundance of forest specialists and canopy foragers were significantly higher in protected forests. These findings suggest that unprotected, disturbed tropical montane forests in Ethiopia help to achieve conservation aims in an area recognized for its global biodiversity importance. At the same time, intact forest ecosystems need continued protection to maximize functional heterogeneity associated with specialist tropical forest taxa.


Intense short-wavelength light triggers avoidance response by Red-tailed Hawks: A new tool for raptor diversion?
Carol R. Foss, Donald J. Ronning and David A. Merker

Abstract

Collisions between birds and aircraft present serious safety and economic risks to aviation worldwide. Research into the potential for lighting to reduce collision risk has been evolving since the mid-twentieth century. Our objective was to explore the potential for using customized light-emitting diodes (LEDs) as a deterrent to wild raptors under natural conditions. The Red-tailed Hawk (Buteo jamaicensis) is among the top 10 bird species struck by aircraft in the United States; these collisions have resulted in aircraft damage, emergency landings, aborted takeoffs, and human injuries and fatalities. We tested the reactions of migrating Red-tailed Hawks to pulsing, high-brightness, monochromatic LEDs that targeted the avian photoreceptors for light of short and extremely short wavelengths. We installed 3 lighting units to illuminate 2 lures at a raptor banding station during the peak of Red-tailed Hawk migration and compared the number of captures and aborted approaches to these lures with captures and aborted approaches at a control station. The proportion of Red-tailed Hawks that aborted their approaches to lures at the treatment station was >5 times that of hawks that aborted approaches at the control site. We observed individuals abruptly changing flight direction as they neared the illuminated lures. Our results suggest that, with further testing and refinement, high-brightness, monochromatic LEDs that specifically target avian photoreceptors could provide a useful tool to divert raptors from hazardous situations.


Winter diet of Bobolink, a long-distance migratory grassland bird, inferred from feather isotopes
Rosalind B. Renfrew, Jason M. Hill, Daniel H. Kim, Christopher Romanek and Noah G. Perlut

Abstract

Effective conservation of migratory bird populations depends on advancements in our understanding of processes throughout the life cycle. Fundamental information about wintering ecology (e.g., habitat use and diet composition) remains limited, which limits assessment of threats to populations during winter. Bobolink (Dolichonyx oryzivorus) is a year-round grassland obligate and Nearctic-Neotropical migrant that undergoes 2 complete molts each year, including a complete prealternate molt on the South American wintering grounds. This unusual winter molt provides a rare opportunity to examine, using stable isotope analysis, the timing and contribution of foraging resources in the Bobolink diet prior to northbound migration from disparate breeding populations. We compared winter diet composition among 3 breeding populations of Bobolinks and during 3 stages of winter molt using stable carbon isotope ratios. We used mixing models to compare the ratio of carbon-12 to carbon-13 isotope (δ13C value) in feathers—grown on the wintering grounds but collected from individuals (n = 105) breeding in Vermont, Nebraska, and North Dakota, USA—to estimate diet during early, middle, and late winter molt. Across the 3 breeding populations, Bobolinks relied on C3 sources for nearly one-third of their diet during the winter molt. Isotope data from feathers collected while growing on the wintering grounds from birds in rice vs. non-rice regions supported our assumption that C3 signatures are primarily due to a rice diet. The proportion of rice consumed was highest during late molt, corresponding with a period of greater rice availability to Bobolinks. Our results demonstrate that rice was a substantial component of the diet throughout the winter molt and was most exploited prior to northbound migration. Research is needed on the potential trade-offs of feeding on abundant cultivated rice, including its nutritional value and associated risks and conflicts from foraging in an agricultural setting.


The establishment threat of the obligate brood-parasitic Pin-tailed Whydah (Vidua macroura) in North America and the Antilles 
Robert Crystal-Ornelas, Julie L. Lockwood, Phillip Cassey and Mark E. Hauber

Abstract

The Pin-tailed Whydah (Vidua macroura) is a generalist obligate brood parasitic bird native to Africa, frequently found in the pet trade, which has successfully established exotic populations in 2 biodiversity hotspots in the Americas. We analyze the species' potential future distribution by identifying key locations in the continental United States, Hawaii, and the Antilles that contain suitable climatic characteristics, host species, and habitat requirements. We used species distribution modeling (MaxEnt) to depict the geographic patterns of possible Pin-tailed Whydah establishment and compared the predictive power of models that included combinations of climatic data (“climate”), land cover (“habitat”), and localities of historical and one known novel host (“hosts”). The preferred model, the “hosts” model, was the highest performing. The most important variable characterizing Pin-tailed Whydah distribution in the preferred model was the presence of a frequent historical host that is also established in the Americas, the Common Waxbill (Estrilda astrild), followed by a less frequent historical host, the Bronze Mannikin (Spermestes cucullata). Our research demonstrates that in the continental United States, Hawaii, and the Antilles, there are locations that possess the needed exotic host species that may facilitate further invasion by the Pin-tailed Whydah. Given that Pin-tailed Whydahs are known to exploit >20 host species from 4 families of birds, clear next steps include assessing their ability to parasitize novel, native species within the highly suitable areas identified in this research.


How will sea-level rise affect threats to nesting success for Seaside Sparrows?
Elizabeth A. Hunter

Abstract

Sea-level rise (SLR) threatens the nesting success of salt marsh breeding birds, including Seaside Sparrows (Ammodramus maritimus), by increasing the magnitude and frequency of extreme high tides that flood nests. However, the threat to nesting success from tidal flooding is intertwined with that of predation because the threats are connected through a trade-off along a nest height gradient. Therefore, to understand the risk to nesting success from SLR, it is necessary to consider predation threats simultaneously. I used an individual-based model of Seaside Sparrow nesting behavior, calibrated using empirical data on nest success rates and nest-site selection behaviors, to project the effects of SLR conditions on the relative importance of predation and flooding threats in affecting nesting success, and to investigate whether nest-site selection along a gradient of nest height can modulate the risk of SLR. Outputs from the model revealed that present-day levels of predation risk pose as great a risk to nesting success as tidal flooding under simulated SLR conditions with extreme flooding risks. Nest success rates could become very low under extreme SLR scenarios, especially when predation risk is very high. The risks of failure from either threat are linked through nest-site selection behaviors: In high-predation-risk seasons, failure probability from flooding is greater than it would be under lower predation risk, due to the predation avoidance behavior of nesting closer to the ground. Therefore, management actions to reduce the risk of excessive failures from predation could reduce the risk of failures from both threats—a potentially useful management strategy, given that controlling predation is more tractable than controlling increased flooding from SLR at a local level.


Territory and nest site selection patterns by Grasshopper Sparrows in southeastern Arizona
Janet M. Ruth and Susan K. Skagen

Abstract

Grassland bird populations are showing some of the greatest rates of decline of any North American birds, prompting measures to protect and improve important habitat. We assessed how vegetation structure and composition, habitat features often targeted for management, affected territory and nest site selection by Grasshopper Sparrows (Ammodramus savannarum ammolegus) in southeastern Arizona. To identify features important to males establishing territories, we compared vegetation characteristics of known territories and random samples on 2 sites over 5 years. We examined habitat selection patterns of females by comparing characteristics of nest sites with territories over 3 years. Males selected territories in areas of sparser vegetation structure and more tall shrubs (>2 m) than random plots on the site with low shrub densities. Males did not select territories based on the proportion of exotic grasses. Females generally located nest sites in areas with lower small shrub (1–2 m tall) densities than territories overall when possible and preferentially selected native grasses for nest construction. Whether habitat selection was apparent depended upon the range of vegetation structure that was available. We identified an upper threshold above which grass structure seemed to be too high and dense for Grasshopper Sparrows. Our results suggest that some management that reduces vegetative structure may benefit this species in desert grasslands at the nest and territory scale. However, we did not assess initial male habitat selection at a broader landscape scale where their selection patterns may be different and could be influenced by vegetation density and structure outside the range of values sampled in this study.


Grassland bird community and acoustic complexity appear unaffected by proximity to a wind energy facility in the Nebraska Sandhills 
Edward J. Raynor, Cara E. Whalen, Mary Bomberger Brown and Larkin A. Powell

Abstract

The placement of wind energy facilities on the landscape is a potential source of direct mortality for wildlife, but indirect effects of wind facilities on natural communities are less well known. An anthropogenically altered acoustic environment may render habitat unsuitable for species that use vocalizations to communicate. We listened to sound recordings to identify the species assemblage of common breeding birds in an unfragmented grassland in the Nebraska Sandhills (USA) in the vicinity of a wind energy facility. From the recordings, we calculated the Acoustic Complexity Index (ACI), which we used to assess differences in the avian community between a reference area (>760 m from any turbines) and a treatment area (<760 m from turbines). We did not observe differences at the assemblage level using univariate metrics of diversity: mean species richness (3.48 vs. 3.25 species per recording event) and Whittaker βw index (6.03 vs. 5.85 species turnover of habitat type) or the ACI (0.17 vs. 0.15). ACI increased with the progression of the breeding season and was correlated with species richness, indicating that ACI provides a useful estimate of acoustic activity of grassland songbirds. The limited habitat perforation caused by wind energy facilities and roads (1% in the area of the wind energy facility) and the low-frequency noise emitted by operational wind turbines did not appear to affect the presence or singing behavior of breeding passerine birds in this landscape.


Post-fledging habitat use in the Dickcissel
Todd M. Jones, Jeffrey D. Brawn and Michael P. Ward

Abstract

Effective habitat management requires understanding habitat needs across a species' life history stages. In songbirds, management of breeding habitat is generally focused on the pre-nesting and nesting stages, while habitat use during the critical post-fledging stage remains understudied and is seldom a target for management. In 2014 and 2015, we documented post-fledging habitat use of Dickcissels (Spiza americana) in central Illinois, USA. We examined vegetation characteristics used by fledglings and how fledgling survival varied with habitat use. We also compared fledgling habitat use to nesting site habitat. Fledgling Dickcissels used areas with vegetation that was overall denser and more concealed than at random locations. Fledglings preferentially selected dense vegetation after fledging (days 1–3 post-fledging), and then used even denser vegetation once they became more mobile (days 4–11 post-fledging). Fledglings that used comparatively denser habitat were more likely to survive the critical part of the post-fledgling period (days 0–3 post-fledging), but not during subsequent parts of the post-fledging period (>3 days post-fledging). Habitat characteristics preferred by fledglings did not differ from those preferred by females for nest sites. Our results suggest that dense vegetation is needed for fledglings until they develop adequate mobility to evade predators. Furthermore, our finding of a positive association between fledgling survival and denser habitat during, but not after, the critical part (days 0–3) of the post-fledging period identifies an important window for management to increase fledgling survival. Management for dense habitat, however, must be appropriately timed not to disturb adults, nests, and young, immobile fledglings.


RESEARCH ARTICLES


Developing spatial models to guide conservation of grassland birds in the U.S. Northern Great Plains
Neal D. Niemuth, Michael E. Estey, Sean P. Fields, Brian Wangler, Andy A. Bishop, Pamela J. Moore, Roger C. Grosse and Adam J. Ryba

Abstract

Conservation of bird populations is increasingly focused on landscapes. We combined data collected in 2005–2011 from 16,250 North American Breeding Bird Survey (BBS) survey points with local and remotely sensed environmental data to model the distribution of 7 grassland bird species in the Northern Great Plains of the United States. We analyzed data at the survey point level, which is consistent with the scale of conservation treatments that we apply, and avoided information loss caused by pooling data at the BBS route level. By accounting for observer effects, nesting of survey points within routes, and sequence of survey points, we accommodated BBS survey design, refined estimates of important habitat predictors, improved model fit, and reduced or eliminated positive spatial autocorrelation in model residuals. The predictive power of models was greatly increased by including variables that characterized annual and long-term precipitation, as well as local land cover attributes not available from satellite-derived land cover data. Occurrence models from survey-point-level BBS data and environmental data with high thematic resolution were able to describe habitat relationships that are often associated with fine-grained, local studies, but across broad spatial extents and at scales relevant to local conservation actions. Predicted occurrence was strongly correlated with observed numbers, suggesting that occurrence models may be useful indicators of density. Relationships derived from models allowed us to develop spatially explicit decision support tools, which can be used to target areas for conservation treatments and to assess the conservation actions of multiple conservation programs and joint ventures (e.g., Prairie Pothole, Rainwater Basin, and Northern Great Plains joint ventures) in the U.S. Northern Great Plains.


REVIEWS

The role of the North American Breeding Bird Survey in conservation 
Marie-Anne R. Hudson, Charles M. Francis, Kate J. Campbell, Constance M. Downes, Adam C. Smith and Keith L. Pardieck

Abstract

The North American Breeding Bird Survey (BBS) was established in 1966 in response to a lack of quantitative data on changes in the populations of many bird species at a continental scale, especially songbirds. The BBS now provides the most reliable regional and continental trends and annual indices of abundance available for >500 bird species. This paper reviews some of the ways in which BBS data have contributed to bird conservation in North America over the past 50 yr, and highlights future program enhancement opportunities. BBS data have contributed to the listing of species under the Canadian Species at Risk Act and, in a few cases, have informed species assessments under the U.S. Endangered Species Act. By raising awareness of population changes, the BBS has helped to motivate bird conservation efforts through the creation of Partners in Flight. BBS data have been used to determine priority species and locations for conservation action at regional and national scales through Bird Conservation Region strategies and Joint Ventures. Data from the BBS have provided the quantitative foundation for North American State of the Birds reports, and have informed the public with regard to environmental health through multiple indicators, such as the Canadian Environmental Sustainability Indicators and the U.S. Environmental Protection Agency's Report on the Environment. BBS data have been analyzed with other data (e.g., environmental, land cover, and demographic) to evaluate potential drivers of population change, which have then informed conservation actions. In a few cases, BBS data have contributed to the evaluation of management actions, including informing the management of Mourning Doves (Zenaida macroura), Wood Ducks (Aix sponsa), and Golden Eagles (Aquila chrysaetos). Improving geographic coverage in northern Canada and in Mexico, improving the analytical approaches required to integrate data from other sources and to address variation in detectability, and completing the database, by adding historical bird data at each point count location and pinpointing the current point count locations would further enhance the survey's value.


RESEARCH ARTICLES

Model selection for the North American Breeding Bird Survey: A comparison of methods
William A. Link, John R. Sauer and Daniel K. Niven

Abstract

The North American Breeding Bird Survey (BBS) provides data for >420 bird species at multiple geographic scales over 5 decades. Modern computational methods have facilitated the fitting of complex hierarchical models to these data. It is easy to propose and fit new models, but little attention has been given to model selection. Here, we discuss and illustrate model selection using leave-one-out cross validation, and the Bayesian Predictive Information Criterion (BPIC). Cross-validation is enormously computationally intensive; we thus evaluate the performance of the Watanabe-Akaike Information Criterion (WAIC) as a computationally efficient approximation to the BPIC. Our evaluation is based on analyses of 4 models as applied to 20 species covered by the BBS. Model selection based on BPIC provided no strong evidence of one model being consistently superior to the others; for 14/20 species, none of the models emerged as superior. For the remaining 6 species, a first-difference model of population trajectory was always among the best fitting. Our results show that WAIC is not reliable as a surrogate for BPIC. Development of appropriate model sets and their evaluation using BPIC is an important innovation for the analysis of BBS data.


Combined analysis of roadside and off-road breeding bird survey data to assess population change in Alaska
Colleen M. Handel and John R. Sauer

Abstract

Management interest in North American birds has increasingly focused on species that breed in Alaska, USA, and Canada, where habitats are changing rapidly in response to climatic and anthropogenic factors. We used a series of hierarchical models to estimate rates of population change in 2 forested Bird Conservation Regions (BCRs) in Alaska based on data from the roadside North American Breeding Bird Survey (BBS) and the Alaska Landbird Monitoring Survey, which samples off-road areas on public resource lands. We estimated long-term (1993–2015) population trends for 84 bird species from the BBS and short-term (2003–2015) trends for 31 species from both surveys. Among the 84 species with long-term estimates, 11 had positive trends and 17 had negative trends in 1 or both BCRs; negative trends were primarily found among aerial insectivores and wetland-associated species, confirming range-wide negative continental trends for many of these birds. Three species with negative trends in the contiguous United States and southern Canada had positive trends in Alaska, suggesting different population dynamics at the northern edges of their ranges. Regional population trends within Alaska differed for several species, particularly those represented by different subspecies in the 2 BCRs, which are separated by rugged, glaciated mountain ranges. Analysis of the roadside and off-road data in a joint hierarchical model with shared parameters resulted in improved precision of trend estimates and suggested a roadside-related difference in underlying population trends for several species, particularly within the Northwestern Interior Forest BCR. The combined analysis highlights the importance of considering population structure, physiographic barriers, and spatial heterogeneity in habitat change when assessing patterns of population change across a landscape as broad as Alaska. Combined analysis of roadside and off-road survey data in a hierarchical framework may be particularly useful for evaluating patterns of population change in relatively undeveloped regions with sparse roadside BBS coverage.


PERSPECTIVE

The first 50 years of the North American Breeding Bird Survey
John R. Sauer, Keith L. Pardieck, David J. Ziolkowski Jr., Adam C. Smith, Marie-Anne R. Hudson, Vicente Rodriguez, Humberto Berlanga, Daniel K. Niven and William A. Link

Abstract

The vision of Chandler (Chan) S. Robbins for a continental-scale omnibus survey of breeding birds led to the development of the North American Breeding Bird Survey (BBS). Chan was uniquely suited to develop the BBS. His position as a government scientist had given him experience with designing and implementing continental-scale surveys, his research background made him an effective advocate of the need for a survey to monitor pesticide effects on birds, and his prominence in the birding community gave him connections to infrastructure—a network of qualified volunteer birders who could conduct roadside surveys with standardized point counts. Having started in the eastern United States and the Atlantic provinces of Canada in 1966, the BBS now provides population change information for ∼546 species in the continental United States and Canada, and recently initiated routes in Mexico promise to greatly expand the areas and species covered by the survey. Although survey protocols have remained unchanged for 50 years, the BBS remains relevant in a changing world. Several papers that follow in this Special Section of The Condor: Ornithological Advances review how the BBS has been applied to conservation assessments, especially in combination with other large-scale survey data. A critical feature of the BBS program is an active research program into field and analytical methods to enhance the quality of the count data and to control for factors that influence detectability. Papers in the Special Section also present advances in BBS analyses that improve the utility of this expanding and sometimes controversial survey. In this Perspective, we introduce the Special Section by reviewing the history of the BBS, describing current analyses, and providing summary trend results for all species, highlighting 3 groups of conservation concern: grassland-breeding birds, aridland-breeding birds, and aerial insectivorous birds.

REVIEWS

Use of North American Breeding Bird Survey data in avian conservation assessments
Kenneth V. Rosenberg, Peter J. Blancher, Jessica C. Stanton and Arvind O. Panjabi

Abstract

Conservation resources are limited, and prioritizing species based on their relative vulnerability and risk of extinction is a fundamental component of conservation planning. In North America, the conservation consortium Partners in Flight (PIF) has developed and implemented a data-driven species assessment process, at global and regional scales, based on quantitative vulnerability criteria. This species assessment process has formed the biological basis for PIF's continental and regional planning and has informed the ranking and legal listing of bird species for conservation protection by state, provincial, and national agencies in Canada, the U.S., and Mexico. Because of its long time series, extensive geographic and species coverage, standardized survey methods, and prompt availability of results, the North American Breeding Bird Survey (BBS) has been an invaluable source of data, allowing PIF to assign objective vulnerability scores calibrated across more than 460 landbird species. BBS data have been most valuable for assessing long-term population trends (PT score). PIF has also developed methods for estimating population size by extrapolating from BBS abundance indices, allowing the assignment of categorical population size (PS) scores for landbird species. At regional scales, BBS relative abundance indices have allowed PIF to assess the area importance (i.e. stewardship responsibility) of each Bird Conservation Region (BCR) for each species, using measures of both relative density and percent of total population in each BCR. Besides direct applicability to assessment scores, PIF has recently used BBS trend data to create new metrics of conservation urgency (e.g., ‘half-life'), as well as for setting population objectives for tracking progress toward meeting conservation goals. Future directions include integrating BBS data with other sources (e.g., eBird) to assess additional species and nonbreeding season measures, working closely with BBS coordinators to expand surveys into Mexico, and providing assessment scores at implementation-relevant scales, such as for migratory bird joint ventures.

RESEARCH ARTICLES

How well do route survey areas represent landscapes at larger spatial extents? An analysis of land cover composition along Breeding Bird Survey routes
Joseph A. Veech, Keith L. Pardieck and David J. ZiolkowskiJr.

Abstract

The occurrence of birds in a survey unit is partly determined by the habitat present. Moreover, some bird species preferentially avoid some land cover types and are attracted to others. As such, land cover composition within the 400 m survey areas along a Breeding Bird Survey (BBS) route clearly influences the species available to be detected. Ideally, to extend survey results to the larger landscape, land cover composition within the survey area should be similar to that at larger spatial extents defining the landscape. Such representativeness helps minimize possible roadside effects (bias), here defined as differences in bird species composition and abundance along a roadside as compared to a larger surrounding landscape. We used land cover data from the 2011 National Land Cover Database to examine representativeness of land cover composition along routes. Using ArcGIS, the percentages of each of 15 land cover types within 400 m buffers along 2,696 U.S. BBS routes were calculated and compared to percentages in 2 km, 5 km, and 10 km buffers surrounding each route. This assessment revealed that aquatic cover types and highly urbanized land tend to be slightly underrepresented in the survey areas. Two anthropogenic cover types (pasture/hay and cropland) may be slightly overrepresented in the survey areas. Over all cover types, 92% of the 2,696 routes exhibited “good” representativeness, with <5 percentage points per cover type difference in proportional cover between the 400 m and 10 km buffers. This assessment further supports previous research indicating that any land-cover-based roadside bias in the bird data of the BBS is likely minimal.


Integrating Breeding Bird Survey and demographic data to estimate Wood Duck population size in the Atlantic Flyway
Guthrie S. Zimmerman, John R. Sauer, G. Scott Boomer, Patrick K. Devers and Pamela R. Garrettson

Abstract

The U.S. Fish and Wildlife Service (USFWS) uses data from the North American Breeding Bird Survey (BBS) to assist in monitoring and management of some migratory birds. However, BBS analyses provide indices of population change rather than estimates of population size, precluding their use in developing abundance-based objectives and limiting applicability to harvest management. Wood Ducks (Aix sponsa) are important harvested birds in the Atlantic Flyway (AF) that are difficult to detect during aerial surveys because they prefer forested habitat. We integrated Wood Duck count data from a ground-plot survey in the northeastern U.S. with AF-wide BBS, banding, parts collection, and harvest data to derive estimates of population size for the AF. Overlapping results between the smaller-scale intensive ground-plot survey and the BBS in the northeastern U.S. provided a means for scaling BBS indices to the breeding population size estimates. We applied these scaling factors to BBS results for portions of the AF lacking intensive surveys. Banding data provided estimates of annual survival and harvest rates; the latter, when combined with parts-collection data, provided estimates of recruitment. We used the harvest data to estimate fall population size. Our estimates of breeding population size and variability from the integrated population model (N̄ = 0.99 million, SD = 0.04) were similar to estimates of breeding population size based solely on data from the AF ground-plot surveys and the BBS (N̄ = 1.01 million, SD = 0.04) from 1998 to 2015. Integrating BBS data with other data provided reliable population size estimates for Wood Ducks at a scale useful for harvest and habitat management in the AF, and allowed us to derive estimates of important demographic parameters (e.g., seasonal survival rates, sex ratio) that were not directly informed by data.



Tuesday, 2 May 2017

The Auk. April 2017: Volume 134, Issue 2

The Auk
Published by: American Ornithological Society


Table of Contents
Apr 2017 : Volume 134 Issue 2 


RESEARCH ARTICLES

Interpopulation variation in nest architecture in a secondary cavity-nesting bird suggests site-specific strategies to cope with heat loss and humidity
Esteban Botero-Delgadillo, Nicole Orellana, Daniela Serrano, Yanina Poblete and Rodrigo A. Vásquez

Abstract
Nest morphology can affect the breeding success of birds. Thus, birds inhabiting different environments may experience divergent selection for nest structure and composition that results in intraspecific geographic variation in nest architecture. We describe interpopulation differences in nest architecture among Thorn-tailed Rayaditos (Aphrastura spinicauda) in 2 contrasting environments near the species' distribution limits: a temperate and very humid environment in north-central Chile (the forest relicts of Fray Jorge National Park; 30°38′S, 71°40′W) and a cold and windy sub-Antarctic environment in the south of Chile (Isla Navarino; 55°4′S, 67°40′W). We collected a total of 62 nests from Fray Jorge and 61 nests from Navarino in 2013 and 2014, measured their dimensions, and quantified their constitutive materials. We tested the nests' thermal properties (simulating heat loss by convection and conduction) and hygroscopic features (water absorption and water loss capacity) and used general linear models to (1) compare these properties between populations and (2) test for a relationship between nest morphology and function. Nests from the northern population exhibited lower rates of heat loss by convection because they were larger and had a lower ratio of surface area to volume; these nests also absorbed less water, probably because of their greater content of plant-derived materials. In the southern population, nests were more compact and better insulated with feathers and hairs, with lower rates of heat loss by conduction. By separately analyzing the roles of convection, conduction, and humidity, our results suggest that potential trade-offs (insulation–humidity) could be differently affecting the nest-building behavior of these populations. Therefore, Thorn-tailed Rayaditos may be using site-specific strategies to cope with the local climate in contrasting environments.


Diet history effects on Zebra Finch incubation performance: Nest attendance, temperature regulation, and clutch success
Kerianne M. Wilson, Michelle Kem and Nancy Tyler Burley

Abstract
Incubation is a costly phase of avian reproduction, as parents must invest in heat transfer to eggs and nest construction in order to maintain egg temperature within suitable thermal limits; however, costs may differ based on an individual's ability to invest in reproduction. To investigate how environmental conditions, specifically food quality experienced during development and reproduction, influence tactics of resource allocation and costs during incubation, captive Zebra Finches (Taeniopygia guttata castanotis) were raised on either a high- or low-quality diet, paired with a bird of the same diet history, and randomly assigned to breed under the same diet they had been reared on or on the opposite diet. Data were collected on nest attendance, nest quality, nest temperature, and clutch performance (clutch size, egg weight, and number of hatchlings). Greater nest attendance and higher nest-quality scores predicted low temperature fluctuation. Three structural nest components also contributed to temperature maintenance. Temperature fluctuation was the only measure to predict whether or not one or more eggs hatched (“clutch fate”); thus, multiple factors interact to contribute to the outcome of a clutch. Allocation to clutch size and egg mass was influenced only by breeding diet, while nest quality was influenced only by natal diet. In contrast, nest attendance and nest temperature varied with both natal and breeding diets. Nest attendance patterns of birds that experienced a consistently high-quality food environment suggest they faced relatively lower reproductive costs and less sexual conflict than other treatments. Nest temperature patterns of birds raised in a high-quality food environment but bred on a low one suggest they faced higher reproductive costs and more sexual conflict. Thus, a good start in early life may be advantageous if conditions remain favorable, but could lead to higher sexual conflict and reproductive costs if food conditions deteriorate in adulthood.


Demographic history of Heermann's Gull (Larus heermanni) from late Quaternary to present: Effects of past climate change in the Gulf of California
Enrico A. Ruiz, Enriqueta Velarde and Andres Aguilar

Abstract
Climate change during the late Quaternary period (LQP), in both temperate and tropical zones, has been a major driver in the shaping of species distributions and abundances. Our understanding of the various effects of climate change on population dynamics of marine species in temperate zones (such as the Gulf of California) is growing. However, studies on the demographic history of seabirds are rare and there is no description of how regional climate change has affected high-trophic-level marine species such as Heermann's Gull (Larus heermanni; Charadriiformes: Laridae). We investigated whether the demographic history of Heermann's Gull reflects population change consistent with past changes in climate in the Gulf of California during the LQP. We also explored whether those past changes affected the demographic history of codistributed marine organisms in a similar way as found for Heermann's Gulls. To test our hypotheses, we sequenced a fragment of the mitochondrial DNA cytochrome b gene (1,033 base pairs) and performed tests to investigate whether demographic change occurred within the LQP. The results of the 3 approaches used were consistent with a historical demographic expansion during the LQP. All analyses (Fu's FS test, Tajima's D neutrality test, mismatch distribution analysis [MDA] and associated demographic parameters, and Bayesian skyline plots [BSP]) were consistent with a model of population expansion in Heermann's Gulls. The MDA estimated the expansion event at ∼48,000 yr before present (yr BP; 95% confidence interval: 34,000–72,000), whereas the BSP showed that population growth began ∼100,000 yr BP and lasted until ∼45,000 yr BP. We discuss possible associations between the demographic expansion of this seabird species and large-scale ecological shifts or demographic expansions of other marine species.


A bare-part ornament is a stronger predictor of dominance than plumage ornamentation in the cooperatively breeding Australian Swamphen
Cody J. Dey, James S. Quinn, Ash King, Jessica Hiscox and James Dale

Abstract
Many animals use coloration to signal dominance and fighting ability. In birds, plumage coloration is often linked to individual quality, but less research has investigated coloration in unfeathered traits (i.e. ‘bare parts'), despite theoretical expectations that they might be more reliable signals. Here, we investigate the relationship between multiple ornaments and social dominance in a wild population of the cooperatively breeding Australian Swamphen (known locally as and hereafter referred to as Pūkeko; Porphyrio melanotus melanotus) to test the hypothesis that bare-part ornaments should be more strongly correlated with dominance than plumage coloration. We show that the size and color of the pūkeko's frontal shield (a bare-part ornament), as well as the brightness and chroma of the blue-UV breast plumage, are correlated with social dominance in adult birds. However, the correlation between frontal shield size and dominance was much higher than that between plumage color and dominance, and was also higher than most previously published correlations between plumage traits and dominance. Additionally, frontal shield size, but not breast coloration, was correlated with the size of the testes in male pūkekos, which may be because bare-part ornaments are more closely tied to an individual's current physiology than plumage ornaments. While correlative, our results demonstrate that bare-part and plumage traits could act as redundant ornaments, but with differing reliability, and suggest that future studies on bare-part ornaments will enhance our understanding of dominance signaling.


Brood parasitism by the enigmatic and rare Pavonine Cuckoo in Amazonian Peru
Manuel A. Sánchez-Martínez, Santiago David, Gustavo A. Londoño and Scott K. Robinson

Abstract
Brood parasitism is an uncommon and understudied strategy in Amazonian bird communities, within which only 5 species are known to be brood parasites. We present data on the brood-parasitic behavior of the Pavonine Cuckoo (Dromococcyx pavoninus) in 3 host species of small-bodied flycatchers in the Peruvian Amazon that construct hanging globular nests with side entrances. During the 7 yr of the study, we encountered 74 nests of these 3 hosts, but parasitism occurred only in 9 nests (12.2%) in 2 yr. Only 1 Pavonine Cuckoo egg was deposited in each host nest (n = 7), and eggs were markedly dissimilar in size and coloration between hosts and parasite. Incubation investment per day was slightly higher (4%) for 1 parasitized nest than for nonparasitized nests. Overall, 33% of parasitic eggs (n = 6) hatched; cuckoo nestlings apparently removed host eggs and killed host nestlings. The nestling period lasted 24 days, and the growth-rate constant based on nestling mass (k = 0.23) was slower for parasite nestlings than for their hosts (k = 0.27 and 0.31). Food provisioning rates were greater in 1 parasitized nest (2.1 ± 0.7 feedings hr−1 nestling−1) than in nonparasitized nests (1.1 ± 0.4). Nestling cuckoos may further mimic the plumage of their host nestlings. Our results suggest that Pavonine Cuckoos negatively affect their hosts' breeding success and are engaged in a coevolutionary arms race with hosts that have defenses against parasitism.


Grey Gerygone hosts are not egg rejecters, but Shining Bronze-Cuckoos lay cryptic eggs
Rose Thorogood, Rebecca M. Kilner, and Justin L. Rasmussen

Abstract
Many brood parasites rely on mimicry to prevent the detection of their eggs by hosts, yet most Australasian cuckoo species lay darkly colored eggs while the eggs of their hosts are pale and speckled. In the dimly lit nests of their hosts, these cuckoo eggs may appear cryptic; however, it is unclear if this disguise has evolved to fool hosts or other cuckoos. Recent work suggests that in at least one species of bronze-cuckoo, cuckoos are more likely to reject conspicuous eggs than are hosts, but it remains unclear whether this is common across the species group. Here, we present field experiments on the sole host of the Shining Bronze-Cuckoo (Chalcites lucidus lucidus) in New Zealand, the Grey Gerygone (Gerygone igata; known locally as the Grey Warbler), that explored whether this host ignores cuckoo eggs because they are cryptic. Using an avian vision model, we showed that Shining Bronze-Cuckoo eggs were variable in their conspicuousness, but were more cryptic in host nests than the host's eggs. We then experimentally parasitized all available clutches with model eggs that mimicked darkly or brightly colored cuckoo eggs, or were of maximum conspicuousness (white) as determined by visual modeling. Hosts never rejected our model eggs, nor cuckoo eggs when naturally parasitized. Instead, only cuckoos rejected model eggs: In 3 out of 4 experimental nests that were subsequently parasitized, the model egg was taken and replaced by a cuckoo's egg. Together, these data and previous experiments suggest that competition among cuckoos, rather than rejection by hosts, provides a stronger selection pressure for the evolution of cryptic eggs across the genus Chalcites.


The feasibility of counting songbirds using unmanned aerial vehicles 
Andrew M. Wilson, Janine Barr and Megan Zagorski

Abstract
Obtaining unbiased survey data for vocal bird species is inherently challenging due to observer biases, habitat coverage biases, and logistical constraints. We propose that combining bioacoustic monitoring with unmanned aerial vehicle (UAV) technology could reduce some of these biases and allow bird surveys to be conducted in less accessible areas. We tested the feasibility of the UAV approach to songbird surveys using a low-cost quadcopter with a simple, lightweight recorder suspended 8 m below the vehicle. In a field experiment using playback of bird recordings, we found that small variations in UAV altitude (it hovered at 28, 48, and 68 m) didn't have a significant effect on detections by the recorder attached to the UAV, and we found that the detection radius of our equipment was comparable with detection radii of standard point counts. We then field tested our equipment, comparing songbird detections from our UAV-mounted recorder with standard point-count data from 51 count stations. We found that the number of birds per point on UAV counts was comparable with standard counts for most species, but there were significant underestimates for some—specifically, issues of song masking for a species with a low-frequency song, the Mourning Dove (Zenaida macroura); and underestimation of the abundance of a species that was found in very high densities, the Gray Catbird (Dumetella carolinensis). Species richness was lower on UAV counts (mean = 5.6 species point−1) than on standard counts (8.3 species point−1), but only slightly lower than on standard counts if nonaudible detections are omitted (6.5 species point−1). Excessive UAV noise is a major hurdle to using UAVs for bioacoustic monitoring, but we are optimistic that technological innovations to reduce motor and rotor noise will significantly reduce this issue. We conclude that UAV-based bioacoustic monitoring holds great promise, and we urge other researchers to consider further experimentation to refine techniques.


Plumage pattern dimorphism in a shorebird exhibiting sex-role reversal (Actitis macularius)
Misha Blizard and Stephen Pruett-Jones

Abstract
In birds, both males and females can exhibit socially selected traits, but relatively few studies address the role of female ornaments despite their potential importance in competitive female–female interactions and male mate choice. We investigated the melanized plumage pattern of male and female Spotted Sandpipers (Actitis macularius), a species with sex-role reversal and a polyandrous mating system. While the sexes overlap in the spottiness metrics, females had fewer, but larger and more irregularly shaped spots that covered a greater percentage of their plumage than did males. Feather mite load best explained the first principal component of plumage pattern (i.e. spot size) in females as well as in males. Sandpipers with lower mite loads had larger spots, but this relationship was less strong in males. Considering the second principal component (i.e. spot shape and percent cover), mass, hematocrit levels, and day captured best explained variation across females. Heavier females with higher hematocrit levels were caught later in the season and had more irregular spots and a higher percentage of melanized plumage cover. Spot pattern in recaptured individuals changed with capture year, indicating that spottiness varies within an individual's life. Overall, these results show that although the differences between the sexes are subtle, spottiness in Spotted Sandpipers is a measurably sexually dimorphic trait with females as the more ornamented sex, and that melanized ornaments can be indicators of female, and possibly male, condition.


A new species of tapaculo (Rhinocryptidae: Scytalopus) from the Western Andes of Colombia
F. Gary Stiles, Oscar Laverde-R. and Carlos Daniel Cadena

Abstract
We describe Scytalopus alvarezlopezi from the Western Andes of Colombia. The new species forms part of a distinctive clade of Scytalopus tapaculos (Rhinocryptidae) that also includes S. robbinsi from Ecuador and S. stilesi and S. rodriguezi, which occur on the Central and Eastern Andes of Colombia. S. alvarezlopezi is easily diagnosable from its near relatives by its song and mitochondrial DNA; differences in plumage exist but are more subtle. The species inhabits dense understory vegetation on the floors and lower slopes of ravines in cloud forest at elevations of 1,300 to 2,100 m. On the Pacific slope, its altitudinal distribution is sandwiched between those of S. chocoensis (below) and S. vicinior (above); the latter in turn is replaced higher up by S. spillmanni and S. latrans, but S. alvarezlopezi also occurs at ∼2,000–2,100 m on eastern slopes just below the low ridgeline. All of the latter species are distinguished by vocal and plumage characters. Marked sexual differences in plumage exist in stilesi, but females have yet to be collected for alvarezlopezi and rodriguezi. We consider that S. alvarezlopezi is not threatened at present, but could be potentially vulnerable due to its restricted distribution; it is endemic to Colombia.

COMMENTARY

The mitonuclear compatibility species concept
Geoffrey E. Hill

Abstract
The avian world is packaged into genetic assemblages that we call species. Although ornithologists can, with a few important exceptions, agree on the boundaries among avian gene pools that delimit species, the evolutionary process that created this structured subdivision of Aves remains uncertain and contentious. Moreover, although avian species are recognizable and diagnosable, many bear signatures of recent, often substantial, exchange of nuclear (N) genetic material. As a result, there is debate regarding the process that gives rise to and maintains the genetic structure of avian populations. I propose that a key missing consideration in discussions of speciation is the necessity of coadaptation between N and mitochondrial (mt) genes to enable core energy production via oxidative phosphorylation. Because mt genomes are non-recombining and subject to high mutation rates, they evolve rapidly. Consequently, N and mt coadaptation persists only through perpetual coevolution between mt and N genes. Mitonuclear coevolution leads to rapid divergences in coadapted mitonuclear gene sets whenever there is a disruption in gene flow among populations. As a result, once populations diverge in coadapted mitonuclear genotypes, the reduced fitness of offspring due to mitonuclear incompatibilities prohibits exchange of mt and N-mt genes and effectively isolates individuals with shared coadapted N and mt genotypes. Given these considerations, I propose that avian species can be objectively diagnosed by uniquely coadapted mt and N genotypes that are incompatible with the coadapted mt and N genotype of any other population. According to this mitonuclear compatibility species concept, mitochondrial genotype is the best current method for diagnosing species.

RESEARCH ARTICLES

Kinship and genetic mating system of the Grayish Baywing (Agelaioides badius), a cooperatively breeding Neotropical blackbird 
Cynthia A. Ursino, María Cecilia De Mársico, Juan Carlos Reboreda and Christina Riehl

Abstract
Kin selection theory predicts that extrapair mating should be rare in cooperatively breeding birds. However, most cooperative breeders are not genetically monogamous and the relationship between promiscuity and cooperative breeding remains unclear. This relationship is further complicated by a lack of data. The majority of cooperatively breeding birds live in the tropics, and their genetic mating systems are little known. Here we studied the genetic mating system of the Grayish Baywing (Agelaioides badius), a socially monogamous Neotropical blackbird in which most nesting pairs are assisted by helpers, previously assumed to be offspring of the breeding pair. Grayish Baywings are the primary host of the parasitic Screaming Cowbird (Molothrus rufoaxillaris), and previous studies have found a positive association between brood parasitism and helper recruitment in the last part of the nestling period. We used microsatellite markers to analyze the kinship of 192 individuals in 47 breeding groups, finding that 13% of 153 nestlings (in 38% of 47 nests) resulted from extrapair mating. We also documented 2 instances of conspecific brood parasitism and 1 instance of quasiparasitism (the nestling was sired by the social father, but was unrelated to the social mother). Of 8 helpers that were genotyped, 4 (all males) were offspring of the breeding pair and 4 (2 males, 2 females) were unrelated to both members of the breeding pair. None of the helpers produced offspring within the clutch. These results suggest that, although cooperative breeding is frequent, genetic relatedness between Grayish Baywing helpers and the offspring that they raise is highly variable. Future studies are needed to determine why unrelated helpers assist at Grayish Baywing nests, and to understand the role that brood parasitism may have played in the evolution of cooperative breeding in this species.


What makes a tactile forager join mixed-species flocks? A case study with the endangered Crested Ibis (Nipponia nippon)
Yuanxing Ye, Yiting Jiang, Canshi Hu, Yao Liu, Baoping Qing, Chao Wang, Esteban Fernández-Juricic and Changqing Ding

Abstract
Visual foragers joining mixed-species flocks can enhance foraging and obtain antipredator benefits. However, relatively little is known about the benefits that tactile foragers may obtain by joining mixed-species groups. We investigated the foraging and antipredator benefits that the Crested Ibis (Nipponia nippon), an endangered species, may get while foraging in single-species flocks and in mixed-species flocks with Little Egrets (Egretta garzetta) during the nonbreeding season. We found that in single-species flocks ibises decreased the proportion of time spent vigilant and increased that spent foraging as total flock size increased. Flight initiation distance (FID, distance between a threat and the animal when the latter flees) decreased with flock size particularly in single-species flocks and alert distance (AD, distance between a threat and the animal first exhibiting alert behavior) decreased with flock size in both single- and mixed-species flocks, but was greater in mixed-species flocks. Taken together, these findings suggest that Crested Ibises may use risk dilution, but not collective detection, in single-species flocks, but use dilution, collective detection, and early warning in mixed-species flocks. We also found partial support for the resource exploitative competition hypothesis as probing bout duration increased with flock size. This tactile forager may benefit from joining mixed-species flocks with a visual forager by using collective detection and early warning (responding to the antipredator signals of the other species), but also tolerate some intraspecific competition in mixed-species flocks through resource depletion effects. Our findings have management implications that could be applied to the protection of this endangered species.


Data loggers in artificial eggs reveal that egg-turning behavior varies on multiple ecological scales in seabirds
Corey A. Clatterbuck, Lindsay C. Young, Eric A. VanderWerf, Alexander D. Naiman, Geoff C. Bower and Scott A. Shaffer

Abstract
In most avian species, egg-turning behavior during incubation is vital for proper embryonic development and hatching success. However, changes in turning behaviors are rarely studied across different temporal scales (e.g., day–night or across incubation phases), though the timing of incubation behaviors affects reproductive success. We used data loggers encapsulated in artificial eggs to measure turning rates and angle changes of eggs in Western Gull (Larus occidentalis) and Laysan Albatross (Phoebastria immutabilis) nests. We examined diurnal and daily cycles in egg-turning behaviors across early, middle, and late incubation phases. Our results indicate that (1) egg-turning behaviors remain similar throughout incubation, resulting in a consistent environment for developing chicks; (2) egg-turning rates and angle changes vary according to diurnal cycles and day length in each species; and (3) egg-turning rates, but not angle changes, were similar between species. Egg-turning behaviors may vary among species according to seasonality and geography, and using consistent methodologies to measure egg turning will further clarify the role of egg turning in avian life history and ecology.

REVIEW

Altitudinal bird migration in North America
W. Alice Boyle

Abstract
Altitudinal bird migration involves annual seasonal movements up and down elevational gradients. Despite the fact that species from montane avifaunas worldwide engage in altitudinal migration, the patterns, causes, and prevalence of these movements are poorly understood. This is particularly true in North America where the overwhelming majority of avian migration research has focused on obligate, long-distance, temperate–tropical movements. Elsewhere in the world, most altitudinal migrants are partial migrants, making downhill movements to nonbreeding areas. However, spatial and temporal patterns, the prevalence and predictability of migration at individual and population levels, and the ultimate ecological factors selecting for movement behavior vary considerably among taxa and regions. I conducted a systematic survey of the evidence for altitudinal migration to fill gaps in our understanding of this behavior among the landbirds of North America and Hawaii. Altitudinal migration was as prevalent as in other avifaunas, occurring in >20% of continental North American and nearly 30% of Hawaiian species. Of the species wintering within the USA and Canada, ∼30% engage in altitudinal migrations. Altitudinal migrants are far more common in the West, are taxonomically and ecologically diverse, and North American species exhibit patterns similar to altitudinal migrants elsewhere in the world. Because altitudinal migration systems are relatively tractable, they present excellent opportunities for testing hypotheses regarding migration generally. Altitudinal migration has likely been overlooked in North America due to contingency in the history of ornithological research. Our need to understand the patterns and causes of altitudinal migrations has never been greater due to emerging environmental threats to montane systems.

RESEARCH ARTICLES

Preferential attachment and colonization of the keratinolytic bacterium Bacillus licheniformis on black- and white-striped feathers
Nicholas M. Justyn, Jennifer A. Peteya, Liliana D'Alba and Matthew D. Shawkey

Abstract
Feathers serve numerous functions, from flight to interspecific and intraspecific communication. Melanin has been shown to protect feathers from microbial degradation that might, for example, hinder flight or mate attraction. Most studies have focused on the physical resistance to degradation that melanin provides. However, it has yet to be addressed whether melanin alters bacterial colonization and attachment patterns before degradation. We used the common keratinolytic bacterium Bacillus licheniformis to test for preferential attachment and colonization on feathers with black (melanized) and white (unmelanized) stripes. Using experimental inoculation of Eurasian Three-toed Woodpecker (Picoides tridactylus) feathers in vitro and scanning electron microscopy, we show that B. licheniformis preferentially colonizes white feather stripes nearly twice as often as black feather stripes. These data suggest that melanin, in addition to strengthening feathers, may inhibit colonization of keratinolytic bacteria, with possible implications regarding the mechanisms of exceptional preservation of feathers and melanin in the fossil record.