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Thursday, 28 May 2015

The Condor: May 2015 : Volume 117 Issue 2, Abstracts

The Condor
Published by: Cooper Ornithological Society

Table of Contents
May 2015 : Volume 117 Issue 2, LINK 


The relative importance of multiscale factors in the distribution of Bachman's Sparrow and the implications for ecosystem conservation
Paul J. Taillie, M. Nils Peterson, and Christopher E. Moorman

Recent research has shown that landscape-level changes, namely habitat loss and fragmentation, can play an important role in determining the distribution of species across a variety of ecological systems. However, the influence of these large-scale factors in relation to small-scale factors, such as local vegetation structure or composition, is poorly understood. We used Bachman's Sparrow (Peucaea aestivalis) as a surrogate species to measure the relative importance of local vegetation and large-scale habitat distribution in the Onslow Bight region of North Carolina, USA. We conducted repeated point counts at 232 points within 111 habitat patches between April 10 and July 20, 2011. We then fit a series of single-season occupancy models, including both local and landscape-level predictors, to identify those that best explained the distribution of Bachman's Sparrows. We documented a strong response to vegetation characteristics best maintained via prescribed fire, but the most influential predictor of Bachman's Sparrow occupancy was the amount of habitat within 3 km. Specifically, the probability of Bachman's Sparrow occurrence was close to zero in landscapes comprised of <10% habitat, regardless of local vegetation conditions. Our results illustrate the strong influence of habitat loss on Bachman's Sparrow and likely on other members of this community, many of which are of high conservation concern.

Modeling the demography and population dynamics of a subtropical seabird, and the influence of environmental factors
Susan M. Waugh, Christophe Barbraud, Lynn Adams, Amanda N. D. Freeman, Kerry-Jayne Wilson, Graham Wood, Todd J. Landers, and G. Barry Baker

The use of long-term ecological datasets to explore the importance of the effects of environmental variability on higher predator populations has been focused mainly on high-latitude areas. We modeled the population dynamics of the Westland Petrel (Procellaria westlandica), which spends its time mostly in subtropical waters during both breeding and the interbreeding migration across the Pacific Ocean. We found that the population has slowly increased since the early 1970s, a result of high adult survival, high fecundity (0.6 of all eggs laid survived to fledge) and moderate mean age at first return to the colony (7.7 yr; a recruitment age typical for this genus), strong recruitment rate of juveniles, and negligible emigration. The modeled population trends were supported by similar rates of increase in nest occupancy since 2001 and nest density since 2007. Annual adult survival for breeders was the same for both sexes (0.954, 95% CI: 0.918–0.975) and constant across years. However, nonbreeders had lower survival rates than breeders, and, among nonbreeders, males tended to survive better (0.926, 95% CI: 0.917–0.934) than females (0.917, 95% CI: 0.900–0.931). Breeders transitioned to the nonbreeding state at a rate of 0.232 and nonbreeders to the breeding state at a rate of 0.295. Sea-surface temperature anomalies had a negative effect on adult survival during the breeding period and a positive effect on survival outside the breeding season. Local marine productivity as measured by fishery catches was strongly correlated with adult survival: Years with a greater fish catch were also years of higher adult survival. Despite many threats operating throughout the breeding and foraging range of Westland Petrels, it appears that marine environmental change is a strongly influential factor for the species, with uncertainty in population growth due to predicted increases in sea-surface temperature in the future.

Cowbird responses to aircraft with lights tuned to their eyes: Implications for bird–aircraft collisions
Megan S. Doppler, Bradley F. Blackwell, Travis L. DeVault, and Esteban Fernández-Juricic

Collisions between birds and aircraft (bird strikes) are expensive, risk human lives, and increase bird mortality. Aircraft lighting has been proposed as a potential means of enhancing avian responses to aircraft. Determining the optimal changes to lighting to reduce bird strikes is a complicated problem because avian visual systems differ markedly from that of humans. Icteridae, including Brown-headed Cowbirds (Molothrus ater; hereafter “cowbirds”), are involved in bird strikes, have a well-described visual system, and respond to approaching vehicles and lights. Our goal was to assess cowbirds' responses to a remote-controlled (RC) aircraft fitted with lights tuned to the cowbird eye. On the basis of perceptual modeling (i.e. visual physiology, object and background reflectance, and ambient light conditions), we found that 470-nm lights (“blue” portion of the human spectrum) would be the most conspicuous wavelength for cowbirds. We used field experiments to examine cowbird response to 470-nm light treatments. Cowbirds exhibited alert behaviors to a stationary RC aircraft with lights on (both continuous and pulsing) in less than half the time they took to do so with lights off. In response to an approaching RC aircraft, cowbird alert responses were delayed at higher aircraft speeds with the lights off, and we noted a less pronounced speed effect with pulsing lights. However, this interaction effect of aircraft speed and lighting was eliminated with continuous lights. Additionally, higher ambient noise levels delayed cowbirds' avoidance responses to the RC aircraft, possibly influencing cowbird behavior as a sensory distractor. We suggest that some types of lighting may enhance the birds' detection and visual tracking of aircraft at high speeds and, thus, holds some potential as a means of reducing the frequency of bird strikes. This sensory-based approach also has implications for management of other bird–object collision problems.

Apparent foraging success reflects habitat quality in an irruptive species, the Black-backed Woodpecker
Christopher T. Rota, Mark A. Rumble, Chad P. Lehman, Dylan C. Kesler, and Joshua J. Millspaugh

Dramatic fluctuations in food resources are a key feature of many habitats, and many species have evolved a movement strategy to exploit food resources that are unpredictable in space and time. The availability of food resources may be a particularly strong determinant of habitat quality for irruptive bird species. We studied the apparent foraging success of Black-backed Woodpeckers (Picoides arcticus), an irruptive species that responds opportunistically to pulsed food resources in burned forests and mountain pine beetle (MPB) infestations. Prior investigations revealed that the highest population growth rates of Black-backed Woodpeckers occurred in habitat created by summer wildfire, with intermediate population growth rates in MPB infestations, and the lowest population growth rates in habitats created by prescribed fire in fall. We tested whether apparent foraging success was associated with known habitat quality in order to assess the potential for food availability to regulate population growth. We counted the number of successfully captured wood-boring beetle larvae and “small” prey on each tree that a Black-backed Woodpecker used for foraging and modeled these counts as a function of habitat, tree diameter, number of years postfire, and tree disturbance category. Total apparent foraging success (the sum of observed captures of wood-boring beetle larvae and small prey per tree) did not vary across habitats, but woodpeckers foraging in habitats created by summer wildfire were expected to capture 2.2 and 2.0 times more wood-boring beetles than woodpeckers foraging in habitats created by fall prescribed fire and MPB infestations, respectively. These results suggest that the availability of food resources may contribute to population regulation in this irruptive species. Furthermore, population growth in irruptive species may be highly sensitive to the availability of preferred food resources. Forests recently burned by summer wildfires provide relatively abundant food resources for Black-backed Woodpeckers and represent high-quality habitat for this species of conservation concern.

Urban residents' perceptions of birds in the neighborhood: Biodiversity, cultural ecosystem services, and disservices 
J. Amy Belaire, Lynne M. Westphal, Christopher J. Whelan, and Emily S. Minor

As our world becomes increasingly urbanized, cities are often where we come into contact with the natural world—not just in parks and urban nature preserves, but in more familiar places like residential yards. We conducted bird surveys and social surveys in Chicago-area residential landscapes near forest preserves (primarily in middle- and high-income areas) to examine residents' perceptions of the birds that co-inhabit their neighborhoods and the relationship of those perceptions with characteristics of the bird community. We found that residents value many aspects of neighborhood birds, especially those related to aesthetics and birds' place in the ecosystem. Our results indicate that while birds were generally well liked and annoyances were minor, several common and visible urban species, such as the House Sparrow (Passer domesticus), European Starling (Sturnus vulgaris), and Blue Jay (Cyanocitta cristata), may attract attention for their negative qualities, such as their sounds and effects on personal property. The results also indicate that residents' valuations of ecosystem services are linked to their perceptions of bird species richness rather than the actual species richness, and people may perceive only a subset of the birds in their neighborhoods. Although birds provide many important ecosystem services, perhaps one of their most important roles in cities is as a relatable and likable connecting point between city dwellers and the broader environment.

Scale-dependent and multi-metric nest habitat thresholds for Red-headed Woodpeckers at the northern periphery of their range
Jacob L. Berl, John W. Edwards, and Jeffrey S. Bolsinger

The relation between species occurrence and the structure or composition of habitat can be complex and often varies in a species-specific manner. Sometimes, species–habitat relations are defined by thresholds, or abrupt nonlinear responses to a habitat gradient. Threshold responses are expected when certain habitat features are required for species occurrence. For example, primary cavity-nesting woodpeckers often typify the threshold concept because in the absence of appropriate substrates (decadent wood) large enough for nest cavities, woodpeckers will not occur. In such cases, identifying thresholds is important to ensure that management activities meet minimal (or maximal) habitat requirements of target species. The Red-headed Woodpecker (Melanerpes erythrocephalus) is a species of national conservation concern, and loss of suitable nesting habitat has been suggested as a primary factor in its population declines. Threshold responses may partly explain why this species has gone locally extinct in areas where land-use change resulted in a transition from suitable to unsuitable habitat. Here, we tested whether a regionally important population of Red-headed Woodpeckers in northern New York, near the periphery of the species' range, exhibited threshold responses in their selection of nesting habitat. We used boosted regression trees (BRT) to identify nest habitat thresholds in relation to multiple habitat variables at multiple spatial scales (nest tree, forest patch, and forest stand). We identified nest tree thresholds related to tree decay class (≥33% decadent canopy), cumulative dead limb length (≥4 m), and tree diameter (≥34 cm dbh). Forest patch (vegetation surrounding nest tree; 0.04 ha) thresholds were related to cumulative dead limb length (≥17 m), woody understory height (<12 cm), mean tree diameter (30 cm dbh), and large tree (≥30 cm dbh) density of ≥4. Forest stand thresholds were related to overall stand decadence (on average trees have ≥1% crown decay) and woody understory height (<12 cm). Red-headed Woodpeckers exhibited scale-dependent and multi-metric nest habitat thresholds, which indicate that a lack of suitable nesting habitat (i.e. habitats meeting or exceeding multi-metric and multi-scale criteria) may be limiting population growth near the periphery of the species' range. In particular, the abundance of decadent (dead and decaying) tree resources appears to limit the distribution of suitable habitat. Our objective threshold criteria can be used to identify habitats of high conservation value for this species, or to identify specific habitat features that require management or restoration to increase suitable habitat for this threatened species.

Genomic single-nucleotide polymorphisms confirm that Gunnison and Greater sage-grouse are genetically well differentiated and that the Bi-State population is distinct 
Sara J. Oyler-McCance, R. Scott Cornman, Kenneth L. Jones, and Jennifer A. Fike

Sage-grouse are iconic, declining inhabitants of sagebrush habitats in western North America, and their management depends on an understanding of genetic variation across the landscape. Two distinct species of sage-grouse have been recognized, Greater (Centrocercus urophasianus) and Gunnison sage-grouse (C. minimus), based on morphology, behavior, and variation at neutral genetic markers. A parapatric group of Greater Sage-Grouse along the border of California and Nevada (“Bi-State”) is also genetically distinct at the same neutral genetic markers, yet not different in behavior or morphology. Because delineating taxonomic boundaries and defining conservation units is often difficult in recently diverged taxa and can be further complicated by highly skewed mating systems, we took advantage of new genomic methods that improve our ability to characterize genetic variation at a much finer resolution. We identified thousands of single-nucleotide polymorphisms (SNPs) among Gunnison, Greater, and Bi-State sage-grouse and used them to comprehensively examine levels of genetic diversity and differentiation among these groups. The pairwise multilocus fixation index (FST) was high (0.49) between Gunnison and Greater sage-grouse, and both principal coordinates analysis and model-based clustering grouped samples unequivocally by species. Standing genetic variation was lower within the Gunnison Sage-Grouse. The Bi-State population was also significantly differentiated from Greater Sage-Grouse, albeit more weakly (FST = 0.09), and genetic clustering results were consistent with reduced gene flow with Greater Sage-Grouse. No comparable genetic divisions were found within the Greater Sage-Grouse sample, which spanned the southern half of the range. Thus, we provide much stronger genetic evidence supporting the recognition of Gunnison Sage-Grouse as a distinct species with low genetic diversity. Further, our work confirms that the Bi-State population is differentiated from other Greater Sage-Grouse. The level of differentiation is much less than the divergence between Greater and Gunnison sage-grouse, supporting the idea that the Bi-State represents a unique population within the Greater Sage-Grouse. New genomic methods like the restriction-site-associated DNA (RAD-tag) method used here illustrate how increasing the number of markers and coverage of the genome can better characterize patterns of genetic variation, particularly among recently diverged taxa, providing vital information for conservation and management.

Occupancy of California Spotted Owl sites following a large fire in the Sierra Nevada, California
Derek E. Lee and Monica L. Bond

High-severity forest fire often is presumed to adversely affect the occupancy of territories by California Spotted Owls (Strix occidentalis occidentalis) because these owls are associated with mature and old-growth forests. We used single-season, multi-state occupancy statistics to estimate site occupancy probability for Spotted Owls at 45 historically occupied sites during the breeding season immediately following the 2013 Rim Fire, which was one of the largest forest fires on record in California. We quantified how occupancy probability was influenced by the amount of high-severity fire occurring in mature forested habitat within Protected Activity Centers (PACs). The model-averaged estimate of site-occupancy probability for at least a single owl was 0.922 (±SE = 0.073), which was higher than other published occupancy probability estimates for this subspecies in either burned or long-unburned sites in the Sierra Nevada. Mean site-occupancy probability for pairs was 0.866 (±0.093), and most sites (33) were occupied by pairs. The amount of high-severity fire in the PAC did not affect pair occupancy. Occupancy probability by at least a single bird was negatively correlated with the amount of high severity fire in the PAC but remained >0.89 in 100% high-severity burned PACs. These data add to observations that California Spotted Owls continue to use post-fire landscapes, even when the fires were large and where large areas burned at high severity, suggesting that owls are not generally negatively impacted by high-severity fire. Based on this and other studies of Spotted Owls, fire, and logging, we suggest land managers consider burned forest within and surrounding PACs as potentially suitable California Spotted Owl foraging habitat when planning and implementing management activities, and we recommend against logging burned forest within at least 1.5 km of nests or roosts for the conservation and recovery of this declining subspecies.

Reproductive performance of Kittlitz's Murrelet in a glaciated landscape, Icy Bay, Alaska, USA
Michelle L. Kissling, Scott M. Gende, Stephen B. Lewis, and Paul M. Lukacs

Kittlitz's Murrelet (Brachyramphus brevirostris) is a dispersed-nesting seabird endemic to Alaska and eastern Russia that may have experienced considerable population declines in some parts of its range in the past few decades. Poor reproduction has been suggested as the demographic bottleneck, yet there are no direct estimates of reproduction in a glaciated area where this species reaches its highest densities at sea during the breeding season. The lack of demographic information in glacial habitats has limited our ability to interpret population trends and to clarify whether the presence of glaciers affects reproductive performance. Between 2007 and 2012, we radio-tagged Kittlitz's Murrelets to measure breeding propensity, nesting success, and fecundity in the heavily glaciated landscape of Icy Bay, Alaska, USA. Of 156 radio-tagged birds, 20% were breeders, 68% were potential breeders, and 12% were nonbreeders. Radio-tagged males (29%) were more likely to be breeders compared to females (11%). Across all years, we located 34 Kittlitz's Murrelet nests, 38% of which were successful. Daily nest survival probability (± SE) was 0.979 ± 0.005, with most nests failing during incubation; if extrapolated to a 55-day period from nest initiation to fledging, the nest survival rate was 0.307 ± 0.083. Low fecundity was due largely to low breeding propensity, not low nesting success. For context, we also determined the breeding status of 14 radio-tagged Marbled Murrelets (B. marmoratus), most of which were breeders (79%) and successfully fledged young (69%). Our data demonstrated that Kittlitz's Murrelets were outperformed in all facets of reproduction compared to Marbled Murrelets. Low fecundity estimates for Kittlitz's Murrelet were consistent with a 10% per annum decline in Icy Bay between 2002 and 2012, suggesting that poor reproductive performance contributed to the local population decline of this species.

Minimizing marker mass and handling time when attaching radio-transmitters and geolocators to small songbirds 
Henry M. Streby, Tara L. McAllister, Sean M. Peterson, Gunnar R. Kramer, Justin A. Lehman, and David E. Andersen

Radio-transmitters and light-level geolocators are currently small enough for use on songbirds weighing <15 g. Various methods are used to attach these markers to larger songbirds, but with small birds it becomes especially important to minimize marker mass and bird handling time. Here, we offer modifications to harness materials and marker preparation for transmitters and geolocators, and we describe deployment methods that can be safely completed in 20–60 s per bird. We describe a 0.5-mm elastic sewing thread harness for radio-transmitters that allows nestlings, fledglings, and adults to be marked with the same harness size and reliably falls off to avoid poststudy effects. We also describe a 0.5-mm jewelry cord harness for geolocators that provides a firm fit for >1 yr. Neither harness type requires plastic or metal tubes, rings, or other attachment fixtures on the marker, nor do they require crimping beads, epoxy, scissors, or tying knots while handling birds. Both harnesses add 0.03 g to the mass of markers for small wood-warblers (Parulidae). This minimal additional mass is offset by trimming transmitter antennas or geolocator connection nodes, resulting in no net mass gain for transmitters and 0.02 g added for geolocators compared with conventional harness methods that add >0.40 g. We and others have used this transmitter attachment method with several small songbird species, with no effects on adult and fledgling behavior and survival. We have used this geolocator attachment method on 9-g wood-warblers with no effects on return rates, return dates, territory fidelity, and body mass. We hope that these improvements to the design and deployment of the leg-loop harness method will enable the safe and successful use of these markers, and eventually GPS and other tags, on similarly small songbirds.

Geolocators on Golden-winged Warblers do not affect migratory ecology
Sean M. Peterson, Henry M. Streby, Gunnar R. Kramer, Justin A. Lehman, David A. Buehler, and David E. Andersen

The use of light-level geolocators is increasingly common for connecting breeding and nonbreeding sites and identifying migration routes in birds. Until recently, the mass and size of geolocators precluded their use on songbird species weighing <12 g. Reducing the mass of geolocators, such as by shortening or eliminating the light stalk, may make their deployment on small birds feasible, but may also inhibit their ability to receive light reliably, because small geolocators can be shaded by feathers. Here we report geolocator effects on migratory ecology of Golden-winged Warblers (Vermivora chrysoptera) in Minnesota and Tennessee. We also evaluated whether stalk length influenced precision of location data for birds on the breeding grounds. At 8–10 g, Golden-winged Warblers are the smallest birds to be outfitted with geolocators to date. We found no differences in return rates, inter-annual territory fidelity, or body mass between geolocator-marked individuals and a control group of color-banded individuals. We observed no difference in return rates or variation in estimated breeding locations between birds marked with stalked geolocators and those with stalkless geolocators. Our results suggest that some small songbirds can be safely marked with geolocators. Light stalks appear to be unnecessary for Golden-winged Warblers; the added mass and drag of stalks can probably be eliminated on other small songbirds.

Recreation changes the use of a wild landscape by corvids 
Lauren E. Walker and John M. Marzluff

As urban areas have grown in population, use of nearby natural areas for outdoor recreation has also increased, potentially influencing bird distribution in landscapes managed for conservation. Members of the family Corvidae (crows, ravens, jays, and magpies) have strong interactions with humans and may be directly affected by recreation in wild landscapes. In Mount Rainier National Park, we evaluated the effects of vegetation, visitor use, and the availability of human-subsidized food on the use of landscape features by 4 corvid species: Steller's Jay (Cyanocitta stelleri), Gray Jay (Perisoreus canadensis), Common Raven (Corvus corax), and Clark's Nutcracker (Nucifraga columbiana). We conducted >1,400 point counts across areas that varied in habitat and in the degree of human recreational impact. We calculated predicted occupancy values while allowing for variation in detection probability. In addition to species-specific suites of vegetation and landscape variables, we found that patterns of human recreation, such as visitor use, food subsidy, and amount of road edge, were also significant in explaining corvid distribution. The number of visitors present during point counts was positively associated with Steller's Jay and Clark's Nutcracker use. Common Ravens used areas with fewer people but with a high density of road edge. Gray Jays, Common Ravens, and Clark's Nutcrackers were each more likely to use sites with anthropogenic food subsidy than sites without subsidies. These changes in landscape use may affect the performance of ecosystem services by corvids and could serve as useful and easily measured bioindicators of the impacts of recreation.

Responses of male Greater Prairie-Chickens to wind energy development
Virginia L. Winder, Andrew J. Gregory, Lance B. McNew, and Brett K. Sandercock

Renewable energy resources have received increased attention because of impacts of fossil fuels on global climate change. In Kansas, USA, optimal sites for wind energy development often overlap with preferred habitats of the Greater Prairie-Chicken (Tympanuchus cupido), a lek-mating prairie grouse of conservation concern. We tested for potential effects of energy development on male Greater Prairie-Chickens in north-central Kansas. We captured males at 23 leks located 0.04 to 28 km from wind turbines during a 2-yr preconstruction period (2007–2008) and a 3-yr postconstruction period (2009–2011). First, we tested for effects of proximity to turbines, habitat, and lek size on annual probability of lek persistence and changes in male numbers. We predicted that energy development might result in behavioral avoidance of areas close to turbines, resulting in increased rates of lek abandonment and fewer males attending surviving leks. We found that distance to turbine had a negative effect on lek persistence for leks <8 km from turbines during the postconstruction period, supporting the 8-km buffer zone recommended by the U.S. Fish and Wildlife Service as an offset for wind energy projects. Additionally, lek persistence was positively related to number of males counted at a lek and with grassland cover surrounding the lek. Second, we tested for effects of wind energy development on male body mass. We predicted that degraded habitat conditions might result in decreased body mass for males attending leks near turbines during the postconstruction period. Male body mass was ~2% lower during the postconstruction period, but distance to turbine did not affect body mass. Additional study is needed to determine whether short-term effects of turbines on lek persistence influence population viability of Greater Prairie-Chickens.

When to use social cues: Conspecific attraction at newly created grasslands
John E. Andrews, Jeffrey D. Brawn, and Michael P. Ward

Social cues are often used by birds when selecting breeding habitats, however, little is known about the timing and influence of social cues within or across seasons. The ontogeny of social information within newly available habitat is essentially unknown and potentially relevant to habitat management, as the primary approach of many conservation initiatives is to simply create habitat. We investigated the influence of conspecific attraction via social cues (conspecific playbacks) on newly created grasslands for Grasshopper Sparrows (Ammodramus savannarum) in Central Illinois over a 2-year period. We found that Grasshopper Sparrows quickly locate and settle at newly created grasslands without the need for social cues, however, social cues are used later in the season. At sites where social cues (i.e. conspecific vocalizations) were broadcast the densities of Grasshopper Sparrows were nearly double that of sites without the additional social cues, however, this difference occurred later in the breeding season. We suggest that social cues are more valuable for Grasshopper Sparrows later in the breeding season as a potential cue of the reproductive success of individuals currently at the site, and therefore future reproduction at the site. Grassland birds are experiencing large population declines and the primary conservation approach is to provide additional habitat. By understanding how grassland birds select breeding sites we can better develop and implement conservation plans.

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