Search birdRS Box

Search birdRS blog posts

Browse the Blog Posts

Or scan through the blog archive below for items of interest as only the latest post is shown below, thanks.

Thursday, 11 September 2014

The Condor: August 2014; Volume 116, Issue 3

The Condor

Published by: Cooper Ornithological Society






Table of Contents

August 2014 : Volume 116, Issue 3 

RESEARCH ARTICLES


Demographic heterogeneity among individuals can explain the discrepancy between capture–mark–recapture and waterfowl count results Full Access

Matthieu Guillemain, Roger Pradel, Olivier Devineau, Géraldine Simon, and Michel Gauthier-Clerc
pg(s) 293–302
Abstract
Demographic heterogeneity has long been considered within wildlife populations, but only the modern development of capture–mark–recapture methods allows this to be easily tested and quantified. It is now possible to rapidly assess whether the modeling of heterogeneous populations, in which categories of individuals differ in survival rate, performs better than traditional approaches, in which all individuals are considered equivalent within a sex and age class. Using long-term banding data for 4,703 adult female Green-winged Teal (Anas crecca) from the Camargue, southern France, we show that a heterogeneous model outperformed a homogeneous model. Individuals from the high survival category had a ∼60% annual survival rate, whereas birds in the second category had a survival rate reduced by a factor of 0.76–0.80, depending on the model (i.e. <50%). We could not demonstrate that individuals within the high survival category were larger or heavier. The link between survival rate and potential differences in individual morphometrics or individual behavioral strategies thus remains to be established. Previous studies in which a Green-winged Teal population was modeled as homogeneous suggested it should decline (population growth rate <1), which we also found when using demographic parameters obtained from a homogeneous model. This finding contradicts waterfowl surveys that show a long-term population increase in this flyway. Modeling the population as heterogeneous led to growth rates of 1.03–1.05 (a 3–5% annual increase), numbers consistent with the growth rate inferred from duck counts and that also partly explain how species such as Green-winged Teal can increase in numbers despite large hunting harvest, sustaining harvest to some extent.
Abstract & References : Full Text : PDF (273 KB) 

A multiscale assessment of tree avoidance by prairie birds Full Access

Sarah J. Thompson, Todd W. Arnold, and Courtney L. Amundson
pg(s) 303–315
Abstract
In North America, grassland bird abundances have declined, likely as a result of loss and degradation of prairie habitat. Given the expense and limited opportunity to procure new grasslands, managers are increasingly focusing on ways to improve existing habitat for grassland birds, using techniques such as tree removal. To examine the potential for tree removal to benefit grassland birds, we conducted 446 point counts on 35 grassland habitat patches in the highly fragmented landscape of west-central Minnesota during 2009–2011. We modeled density of four grassland bird species in relation to habitat composition at multiple scales, focusing on covariates that described grass, woody vegetation (trees and large shrubs), or combinations of grass and woody vegetation. The best-supported models for all four grassland bird species incorporated variables measured at multiple scales, including local features such as grass height, litter depth, and local tree abundance, as well as landscape-level measures of grass and tree cover. Savannah Sparrows (Passerculus sandwichensis), Sedge Wrens (Cistothorus platensis), and Bobolinks (Dolichonyx oryzivorus) responded consistently and negatively to woody vegetation, but response to litter depth, grass height, and grassland extent were mixed among species. Our results suggest that reducing shrub and tree cover is more likely to increase the density of grassland birds than are attempts to improve grass quality or quantity. In particular, tree removal is more likely to increase density of Savannah Sparrows and Sedge Wrens than any reasonable changes in grass quality or quantity. Yet tree removal may not result in increased abundance of grassland birds if habitat composition is not considered at multiple scales. Managers will need to either manage at large scales (80–300 ha) or focus their efforts on removing trees in landscapes that contain some grasslands but few nearby wooded areas.
Abstract & References : Full Text : PDF (384 KB) 


COMMENTARY


Using patch occupancy models to estimate area of crevice-nesting seabird colonies Full Access

Joel H. Reynolds and Heather M. Renner
pg(s) 316–324
Abstract
Crevice-nesting seabirds are notoriously difficult to monitor. We present a survey design and analysis that estimates both colony area and geographic extent, using indirect evidence to determine whether a cell is “occupied.” The approach is to define a grid of cells across potential habitat and randomly sample small plots within each cell, surveying for signs of occupancy. Visiting ≥1 plot cell−1 provides a basis for mapping geographic extent. Occupancy models are used to estimate colony area, probability of detection for an occupied cell, and standard errors for all estimated parameters (allowing for statistical comparisons across surveys or colonies). We estimated the area of a colony of Least Auklets (Aethia pusilla) and Crested Auklets (A. cristatella) on Segula Island, Aleutian Archipelago, Alaska, in 2006, and use this as an example of how to adapt the survey design to the logistical constraints common in seabird colony surveys. Surveying only a handful of sample plots of ∼16 m2 in each ∼2,500-m2 cell in the grid was adequate to estimate the detection bias from spatial subsampling, correcting a >50% underestimate of colony area due to plots without evidence having been interpreted as unoccupied cells.
Abstract & References : Full Text : PDF (264 KB) 


RESEARCH ARTICLES


Variation in home-range size of Black-backed Woodpeckers Full Access

Morgan W. Tingley, Robert L. Wilkerson, Monica L. Bond, Christine A. Howell, and Rodney B. Siegel
pg(s) 325–340
Abstract
The Black-backed Woodpecker (Picoides arcticus) is a species of conservation concern that is strongly associated with recently burned forests. Black-backed Woodpeckers are known to have variable home-range sizes, yet the ecological factors related to this variation have not been adequately explored and may hold insights into the natural history of the species and the management of its habitat. During 2011 and 2012, we radio-tracked Black-backed Woodpeckers nesting in 3 forested areas of California that burned between 2 and 5 years before the initiation of tracking. Among 15 individuals with robust tracking data, we found that home-range size varied by an order of magnitude, from 24.1 to 304.1 ha, as measured by movement-based kernel estimation. Using an information-theoretic approach, we evaluated the functional relationship between snag basal area—an a priori key resource—and home-range size, additionally controlling for sex, age, and years since fire as covariates. We found that snag basal area alone best predicted home-range size, explaining 54–62% of observed variation. As snag basal area increased, home-range sizes exponentially decreased. This relationship held true both with and without the inclusion of 3 individuals that nested in burned forest yet foraged predominantly outside the fire perimeter in unburned forest. Snag basal area, unlike other potential influences on home-range size, is an attribute that forest managers can directly influence. We describe a quantitative relationship between home-range size and snag basal area that forest managers can use to predict Black-backed Woodpecker pair density in burned forests and assess the likely population consequences of specific harvest treatments. Given that the birds in our study, foraging primarily in burned forest, all had home ranges with an average snag basal area ≥17 m2 ha−1, this may represent a benchmark for minimum habitat needs in postfire stands.
Abstract & References : Full Text : PDF (1512 KB) 

Landscape alterations influence differential habitat use of nesting buteos and ravens within sagebrush ecosystem: Implications for transmission line development Full Access

Peter S. Coates, Kristy B. Howe, Michael L. Casazza, and David J. Delehanty
pg(s) 341–356
Abstract
A goal in avian ecology is to understand factors that influence differences in nesting habitat and distribution among species, especially within changing landscapes. Over the past 2 decades, humans have altered sagebrush ecosystems as a result of expansion in energy production and transmission. Our primary study objective was to identify differences in the use of landscape characteristics and natural and anthropogenic features by nesting Common Ravens (Corvus corax) and 3 species of buteo (Swainson's Hawk [Buteo swainsoni], Red-tailed Hawk [B. jamaicensis], and Ferruginous Hawk [B. regalis]) within a sagebrush ecosystem in southeastern Idaho. During 2007–2009, we measured multiple environmental factors associated with 212 nest sites using data collected remotely and in the field. We then developed multinomial models to predict nesting probabilities by each species and predictive response curves based on model-averaged estimates. We found differences among species related to nesting substrate (natural vs. anthropogenic), agriculture, native grassland, and edge (interface of 2 cover types). Most important, ravens had a higher probability of nesting on anthropogenic features (0.80) than the other 3 species (<0.10), and the probability of nesting near agriculture was greatest for ravens (0.55) followed by Swainson's Hawk (0.28). We also describe changes in nesting densities over 4 decades at this site as related to natural and anthropogenic disturbances. Since the 1970s, the composition of the raptor and raven nesting community has drastically changed with anthropogenic alterations and loss of continuous stands of sagebrush (Artemisia spp.), favoring increased numbers of nesting ravens and fewer nesting Ferruginous Hawks. Our results indicate that habitat alterations, fragmentation, and forthcoming disturbances anticipated with continued energy development in sagebrush steppe ecosystems can lead to predictable changes in raptor and raven communities.
Abstract & References : Full Text : PDF (347 KB) 

Radar analysis of fall bird migration stopover sites in the northeastern U.S. 

Jeffrey J. Buler and Deanna K. Dawson
pg(s) 357–370
Abstract
The national network of weather surveillance radars (WSR-88D) detects flying birds and is a useful remote-sensing tool for ornithological study. We used data collected during fall 2008 and 2009 by 16 WSR-88D radars in the northeastern U.S. to quantify the spatial distribution of landbirds during migratory stopover. We geo-referenced estimates based on radar reflectivity, of the density of migrants aloft at their abrupt evening exodus from daytime stopover sites, to the approximate locations from which they emerged. We classified bird stopover use by the magnitude and variation of radar reflectivity across nights; areas were considered “important” stopover sites for conservation if bird density was consistently high. We developed statistical models that predict potentially important stopover sites across the region, based on land cover, ground elevation, and geographic location. Large areas of regionally important stopover sites were located along the coastlines of Long Island Sound, throughout the Delmarva Peninsula, in areas surrounding Baltimore and Washington, along the western edge of the Adirondack Mountains, and within the Appalachian Mountains of southwestern Virginia and West Virginia. Locally important stopover sites generally were associated with deciduous forests embedded within landscapes dominated by developed or agricultural lands, or near the shores of major water bodies. Preserving or enhancing patches of natural habitat, particularly deciduous forests, in developed or agricultural landscapes and along major coastlines could be a priority for conservation plans addressing the stopover requirements of migratory landbirds in the northeastern U.S. Our maps of important stopover sites can be used to focus conservation efforts and can serve as a sampling frame for fieldwork to validate radar observations or for ecological studies of landbirds on migratory stopover.

Acoustic monitoring of nocturnally migrating birds accurately assesses the timing and magnitude of migration through the Great Lakes 

Claire E. Sanders and Daniel J. Mennill
pg(s) 371–383
Abstract
Tracking the movements of migratory songbirds poses many challenges because much of their journey takes place at night. One promising technique for studying migratory birds relies on microphones to record the nocturnal flight calls produced by birds on the wing. We compared recordings of night flight calls with bird-banding data in a southern Great Lakes ecosystem. We collected >6,200 hr of nocturnal recordings at 7 locations around Lake Erie. We detected >60,000 flight calls from migratory birds and classified 45,775 calls to species level or to a bioacoustic category comprising several species with similar calls. We compared these acoustic data with records of 5,624 birds captured in mist nets. We found that acoustic recordings accurately quantified the magnitude of migration; comparison with mist-net data revealed significant positive correlations between the number of acoustic detections and the number of mist-net detections across species. We also found that acoustic recordings accurately quantified the timing of migration; we found significant positive correlations between the date of passage of the 10th, 50th, and 90th percentiles of the populations of up to 25 groups of passage migrant species in the acoustic data and mist-net data. A careful examination of 6 species with distinctive flight calls revealed only subtle seasonal differences between peak detections via acoustic monitoring and mist netting, at both daily and weekly timescales. This research enhances our understanding of the role that acoustic sampling can play in monitoring migratory birds, providing important empirical support for the validity of night-flight-call monitoring.

Density, habitat use, and opportunities for conservation of shorebirds in rice fields in southeastern South America Full Access

Rafael Antunes Dias, Daniel E. Blanco, Andrea P. Goijman, and María Elena Zaccagnini
pg(s) 384–393
Abstract
Worldwide, shorebirds are a major component of rice field avian biodiversity. Rice fields in Argentina and southern Brazil hold large numbers of shorebirds and have been recognized as important areas for migrating or wintering species. To develop successful shorebird conservation strategies, we need to understand geographic variation in shorebird abundance in rice fields as well as how bird use of rice fields varies over the rice growing cycle. We surveyed shorebirds in November and December in the main rice cultivation regions of interior Argentina and coastal Brazil to estimate shorebird densities using distance sampling and to evaluate densities of individual species at different stages of the rice cycle. We detected >7,000 shorebirds in rice fields, including a variety of Nearctic migrants. Density of resident species was generally low and showed no differences between countries. Densities of migratory taxa were higher and varied between Brazil and Argentina. Pectoral Sandpiper (Calidris melanotos) and Lesser Yellowlegs (Tringa flavipes) were the most common species in Argentina, but White-rumped Sandpiper (Calidris fuscicollis) and American Golden-Plover (Pluvialis dominica) were the most common species in Brazil. Pectoral Sandpiper density was nearly 8 times higher in Argentina than in Brazil; densities of the White-rumped Sandpiper and American Golden-Plover were 33 and 25 times higher in Brazil than in Argentina. Shorebird density was highest in lightly flooded paddies with rice height <20 cm. Our findings confirm the importance of rice paddies for shorebirds in southeastern South America and emphasize the need for detailed assessments to ensure that agricultural chemical and water management practices are biodiversity friendly.
Abstract & References : Full Text : PDF (640 KB) 

Factors influencing nest survival and renesting by Piping Plovers in the Great Lakes region Full Access

Andrea H. Claassen, Todd W. Arnold, Erin A. Roche, Sarah P. Saunders, and Francesca J. Cuthbert
pg(s) 394–407
Abstract
Renesting is an important breeding strategy used by birds to compensate for nest failure. If birds renest, clutch removal for captive rearing can be used to augment endangered populations; however, not all individuals renest following nest loss, and later nesting attempts may have lower survival rates and clutch sizes. We investigated variation in nest initiation date, clutch size, daily nest survival, renesting propensity, and renesting intervals of federally endangered Great Lakes Piping Plovers (Charadrius melodus) from 1993 to 2010. We also compared productivity under hypothetical clutch removal for captive rearing vs. non-removal scenarios. Nest initiation date was earlier for older adults and was more strongly affected by female than male age. Clutch size and nest survival decreased with later nest initiation, and nest survival increased with male age and nest age until close to hatching. Overall, Piping Plovers replaced 49% of failed nests. Renesting propensity decreased with later date, increased with each successive nesting attempt, and varied according to cause of failure; probability of renesting was highest following flooding and lowest for inviable clutches. Renesting intervals increased with age of the previous nest and averaged 4.2 days longer for birds that changed mates. Results also indicated that, compared to leaving eggs in situ, clutch removal for captive rearing would produce 43% fewer 1-year-old recruits, partly because renesting does not fully offset clutch removal; therefore, efforts to increase fledging success in this endangered population should focus on proactively protecting nests in situ rather than relying on collection of eggs for captive rearing.
Abstract & References : Full Text : PDF (431 KB) 


REVIEW


The persistent problem of lead poisoning in birds from ammunition and fishing tackle 

Susan M. Haig, Jesse D'Elia, Collin Eagles-Smith, Jeanne M. Fair, Jennifer Gervais, Garth Herring, James W. Rivers, and John H. Schulz
pg(s) 408–428
Abstract
Lead (Pb) is a metabolic poison that can negatively influence biological processes, leading to illness and mortality across a large spectrum of North American avifauna (>120 species) and other organisms. Pb poisoning can result from numerous sources, including ingestion of bullet fragments and shot pellets left in animal carcasses, spent ammunition left in the field, lost fishing tackle, Pb-based paints, large-scale mining, and Pb smelting activities. Although Pb shot has been banned for waterfowl hunting in the United States (since 1991) and Canada (since 1999), Pb exposure remains a problem for many avian species. Despite a large body of scientific literature on exposure to Pb and its toxicological effects on birds, controversy still exists regarding its impacts at a population level. We explore these issues and highlight areas in need of investigation: (1) variation in sensitivity to Pb exposure among bird species; (2) spatial extent and sources of Pb contamination in habitats in relation to bird exposure in those same locations; and (3) interactions between avian Pb exposure and other landscape-level stressors that synergistically affect bird demography. We explore multiple paths taken to reduce Pb exposure in birds that (1) recognize common ground among a range of affected interests; (2) have been applied at local to national scales; and (3) engage governmental agencies, interest groups, and professional societies to communicate the impacts of Pb ammunition and fishing tackle, and to describe approaches for reducing their availability to birds. As they have in previous times, users of fish and wildlife will play a key role in resolving the Pb poisoning issue.
Abstract & References : Full Text : PDF (1319 KB) 


PERSPECTIVE


Considering the switch: Challenges of transitioning to non-lead hunting ammunition 

Clinton W. Epps
pg(s) 429–434
Abstract
In this issue of The Condor: Ornithological ApplicationsHaig et al. (2014) summarize negative impacts of lead ammunition and fishing tackle on birds and discuss strategies for mitigating risks to wildlife and human health. Their Review raises an important set of questions for hunters, wildlife managers, and conservation scientists. Effective mitigation will require careful understanding of technical, economic, and social dimensions of the problem. Here, I focus on challenges specific to adopting non-lead ammunition for hunting, particularly for large game animals. I discuss limitations of using the ban on lead ammunition for waterfowl hunting as an analog for reducing lead use for other types of hunting, explain important technical considerations in design and use of non-lead ammunition, and point out areas where effective non-lead alternatives are still lacking. I suggest that currently available economic analyses of the cost of non-lead alternatives are inadequate and do not recognize wide variation in hunter behavior. These considerations have strong implications for designing effective outreach and predicting responses of hunters asked to consider non-lead alternatives. Enforcing outright bans on using lead ammunition for all types of hunting, as recently enacted in California, may prove even more challenging than similar restrictions for waterfowl hunting. Despite this, I propose that major reductions in exposure of wildlife and people to lead bullet fragments are achievable, particularly through outreach and incentive programs that focus on the most commonly used types of firearms for big game hunting—high velocity modern rifles. Bullets from these widely used rifles typically produce the most lead fragments and have the best selection of effective non-lead options available at this time. Efforts to change hunter behavior must recognize the true costs and challenges of changing to non-lead ammunition. Likewise, hunters should recognize and accept their important role in wildlife conservation and work to embrace effective alternatives to lead as they become available.
Abstract & References : Full Text : PDF (189 KB) 


RESEARCH ARTICLES


Stable occupancy by breeding hawks (Buteo spp.) over 25 years on a privately managed bunchgrass prairie in northeastern Oregon, USA Full Access

Patricia L. Kennedy, Anne M. Bartuszevige, Marcy Houle, Ann B. Humphrey, Katie M. Dugger, and John Williams
pg(s) 435–445
Abstract
Potential for large prairie remnants to provide habitat for grassland-obligate wildlife may be compromised by nonsustainable range-management practices. In 1979–1980, high nesting densities of 3 species of hawks in the genus Buteo—Ferruginous Hawk (Buteo regalis), Red-tailed Hawk (B. jamaicensis), and Swainson's Hawk (B. swainsoni)—were documented on the Zumwalt Prairie and surrounding agricultural areas (34,361 ha) in northeastern Oregon, USA. This area has been managed primarily as livestock summer range since it was homesteaded. Unlike in other prairie remnants, land management on the Zumwalt Prairie was consistent over the past several decades; thus, we predicted that territory occupancy of these 3 species would be stable. We also predicted that territory occupancy would be positively related to local availability of nesting structures within territories. We evaluated these hypotheses using a historical dataset, current survey and habitat data, and occupancy models. In support of our predictions, territory occupancy of all 3 species has not changed over the study period of ∼25 yr, which suggests that local range-management practices are not negatively affecting these taxa. Probability of Ferruginous Hawk occupancy increased with increasing area of aspen, an important nest structure for this species in grasslands. Probability of Swainson's Hawk occupancy increased with increasing area of large shrubs, and probability of Red-tailed Hawk occupancy was weakly associated with area of conifers. In the study area, large shrubs and conifers are commonly used as nesting structures by Swainson's Hawks and Red-tailed Hawks, respectively. Availability of these woody species is changing (increases in conifers and large shrubs, and decline in aspen) throughout the west, and these changes may result in declines in Ferruginous Hawk occupancy and increases in Swainson's Hawk and Red-tailed Hawk occupancy in the future.
Abstract & References : Full Text : PDF (434 KB) 

Apparent survival of adult Burrowing Owls that breed in Canada is influenced by weather during migration and on their wintering grounds Full Access

Troy I. Wellicome, Ryan J. Fisher, Ray G. Poulin, L. Danielle Todd, Erin M. Bayne, D. T. Tyler Flockhart, Josef K. Schmutz, Ken De Smet, and Paul C. James
pg(s) 446–458
Abstract
Understanding factors that influence the survival of endangered migratory species is critical for making informed management decisions, yet this understanding relies on long-term recapture datasets for species that are, by definition, rare. Using 3 geographically widespread (Saskatchewan, Alberta, and Manitoba, Canada) and long-term (6–15 yr) mark–recapture datasets, we quantified spatial and temporal variation in apparent annual survival and recapture probabilities of Burrowing Owl (Athene cunicularia), an endangered species that breeds in Canada. We then examined how large-scale weather patterns during migration (storms) and on the wintering and breeding grounds (precipitation), in addition to prey irruptions on the breeding grounds, influenced apparent survival of Burrowing Owls. Female Burrowing Owls had lower apparent survival than males in all 3 study areas. Storms during fall migration and above-average precipitation on the wintering grounds were associated with reduced apparent survival of Burrowing Owls in the longest-running study area, Saskatchewan; in Alberta and Manitoba, there were few correlations between apparent survival of Burrowing Owls and weather or prey irruptions. Increases in stochastic events such as storms during migration or precipitation on the wintering grounds could have adverse consequences on the already small Burrowing Owl population in Canada. Local management actions that focus solely on improving adult apparent survival within Canada are likely insufficient for mitigating susceptibility of adults to inclement weather or other factors outside the breeding season, underscoring the need for management of this species across multiple jurisdictions within North America.
Abstract & References : Full Text : PDF (406 KB) 

Response of avian communities to invasive vegetation in urban forest fragments Full Access

Sarah C. Schneider and James R. Miller
pg(s) 459–471
Abstract
Proliferation of invasive plants in forest understories throughout North America has prompted restoration efforts focused on removal of invasive vegetation. Although the negative impacts of invasives on native plant communities are well documented, effects on forest bird communities remain largely unknown. To address this issue, we examined the response of avian communities to invasive plants in forest fragments across 4 counties in northeastern Illinois, a region characterized by extensive urbanization. We surveyed breeding bird communities in 46 forest plots representing a gradient in abundance of invasive woody plants. We quantified vegetation structure and composition within plots, as well as landscape context. Exotic trees and shrubs were present on all but 3 plots. Although native trees were common, native species represented <7% of total stem density of shrubs. Measures of invasion were weakly correlated with those representing urbanization, yet broad-scale measures of urbanization such as building density and urban cover were strongly associated with avian community structure. At finer scales, measures of invasion were important predictors of the relative abundance of birds in several nesting and foraging guilds. Shrub nesters showed a positive response to invasive vegetation, whereas the relative abundance of aerial salliers and ground nesters decreased with increased proportions of invasive trees. Because restoration strategies aimed at the complete removal of invasive shrubs could diminish habitat quality for some species, thinning of understory vegetation or the removal of invasive trees may confer the greatest benefits to avian communities when few native understory plants are present.
Abstract & References : Full Text : PDF (322 KB) 

No evidence of displacement due to wind turbines in breeding grassland songbirds Full Access

Amanda M. Hale, Erin S. Hatchett, Jeffrey A. Meyer, and Victoria J. Bennett
pg(s) 472–482
Abstract
Projected global growth in wind energy development has the potential to negatively affect wildlife populations, and yet the indirect effects of wind turbines on wildlife (e.g., displacement from otherwise suitable habitat) remain largely understudied, compared with investigations of direct effects (e.g., collision mortality). Thus, over a 3-yr period (2009–2011), we used 2 alternative survey methods to study displacement in breeding grassland songbirds at an operational wind facility in the southern Great Plains, USA. Using a line transect method in 2009 and 2010, we estimated the densities of Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum) within 500 m of wind turbines. Dickcissel density was positively related to vegetation structure and was highest 301–400 m from wind turbines in both years; however, this relationship was confounded by fence lines bisecting transects within this single distance bin. By contrast, we found no such relationships in Eastern Meadowlarks or Grasshopper Sparrows. Using a plot-based method in 2011, we estimated Dickcissel and Grasshopper Sparrow densities within 750 m of wind turbines. Again, we found a strong positive relationship between Dickcissel density and vegetation structure. With the change in survey method, however, the confounding effect of fence lines was removed and the relationship between distance to turbine and Dickcissel density disappeared. Variation in Grasshopper Sparrow density in 2011 was not explained by any variable we measured. In summary, we found no evidence of displacement within 500–750 m of wind turbines in the 3 most abundant breeding grassland songbirds at our site. We caution that it may be difficult to isolate the effect of distance to turbine from other factors that covary with distance (e.g., presence of fence lines) when using a line transect method to study displacement at operational wind facilities.
Abstract & References : Full Text : PDF (774 KB) 

Habitat use and population status of Yellow-billed and Pacific loons in western Alaska, USA Full Access

Joshua H. Schmidt, Melanie J. Flamme, and Johann Walker
pg(s) 483–492
Abstract
Effective conservation of sympatric avian populations depends on unbiased estimates of population size, distribution, and habitat use. For populations of Yellow-billed Loons (Gavia adamsii) and Pacific Loons (G. pacifica) co-occurring in Arctic wetland communities in Alaska, USA, such data are limited and difficult to obtain, hindering population assessments and decision making. The Yellow-billed Loon is also under consideration for additional protections under the Endangered Species Act due to small global population size, specific habitat requirements, and low fecundity, further increasing the need for information at the landscape scale. To help evaluate the population status and habitat use of both species, we used repeated aerial surveys and a dynamic multistate occupancy modeling approach to jointly estimate 1) probability of lake use and 2) probability of use for nesting for Yellow-billed and Pacific loon populations at the landscape scale on the Seward Peninsula and Cape Krusenstern, Alaska, in 2011 and 2013. We also estimated state-specific transition probabilities and degree of interspecific competition to assess population stability and degree of species interactions. We found that probability of site reuse (ϕYellow-billed = 0.73 [0.44–0.94]; ϕPacific = 0.86 [0.72–0.98]) or reuse for nesting (ϕYellow-billed = 0.72 [0.46–0.97]; ϕPacific = 0.59 [0.38–0.85]) in 2013 was high, as was overall use of lakes >7 ha by loons (>80%). These results suggested that lake habitats may have been saturated, and that populations of both species were stable over the two-year interval between surveys. Our estimates indicated that nesting populations in western Alaska were much larger than previously thought for both Yellow-billed (∼2.5 times larger) and Pacific loons (∼1.5–2.0 times larger). Together our results indicate that Arctic wetlands in western Alaska are important for both species and that loon populations in this area warrant additional consideration for conservation.

Minimal changes in heart rate of incubating American Oystercatchers (Haematopus palliatus) in response to human activity Full Access

Tracy E. Borneman, Eli T. Rose, and Theodore R. Simons
pg(s) 493–503
Abstract
An organism's heart rate is commonly used as an indicator of physiological stress due to environmental stimuli. We used heart rate to monitor the physiological response of American Oystercatchers (Haematopus palliatus) to human activity in their nesting environment. We placed artificial eggs with embedded microphones in 42 oystercatcher nests to record the heart rate of incubating oystercatchers continuously for up to 27 days. We used continuous video and audio recordings collected simultaneously at the nests to relate physiological response of birds (heart rate) to various types of human activity. We observed military and civilian aircraft, off-road vehicles, and pedestrians around nests. With the exception of high-speed, low-altitude military overflights, we found little evidence that oystercatcher heart rates were influenced by most types of human activity. The low-altitude flights were the only human activity to significantly increase average heart rates of incubating oystercatchers (12% above baseline). Although statistically significant, we do not consider the increase in heart rate during high-speed, low-altitude military overflights to be of biological significance. This noninvasive technique may be appropriate for other studies of stress in nesting birds.


No comments:

Post a Comment