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Thursday, 19 March 2015

The Condor. February 2015: Volume 117, Issue 1

The Condor
Published by: Cooper Ornithological Society



Table of Contents
Feb 2015 : Volume 117 Issue 1

LINK

EDITORIAL

Don't be afraid to say ‘I study birds' 
Philip C. Stouffer

RESEARCH ARTICLES

Breeding habitat associations and predicted distribution of an obligate tundra-breeding bird, Smith's Longspur 
Teri C. Wild, Steven J. Kendall, Nikki Guldager, and Abby N. Powell

Abstract
Smith's Longspur (Calcarius pictus) is a species of conservation concern which breeds in Arctic habitats that are expected to be especially vulnerable to climate change. We used bird presence and habitat data from point-transect surveys conducted at 12 sites across the Brooks Range, Alaska, 2003–2009, to identify breeding areas, describe local habitat associations, and identify suitable habitat using a predictive model of Smith's Longspur distribution. Smith's Longspurs were observed at seven sites, where they were associated with a variety of sedge–shrub habitats composed primarily of mosses, sedges, tussocks, and dwarf shrubs; erect shrubs were common but sparse. Nonmetric multidimensional scaling ordination of ground cover revealed positive associations of Smith's Longspur presence with sedges and mosses and a negative association with high cover of shrubs. To model predicted distribution, we used boosted regression trees to relate landscape variables to occurrence. Our model predicted that Smith's Longspurs may occur in valleys and foothills of the northeastern and southeastern mountains and in upland plateaus of the western mountains, and farther west than currently documented, over a predicted area no larger than 15% of the Brooks Range. With climate change, shrubs are expected to grow larger and denser, while soil moisture and moss cover are predicted to decrease. These changes may reduce Smith's Longspur habitat quality and limit distribution in the Brooks Range to poorly drained lowlands and alpine plateaus where sedge–shrub tundra is likely to persist. Conversely, northward advance of shrubs into sedge tundra may create suitable habitat, thus supporting a northward longspur distribution shift.


Synergistic effects of spring temperatures and land cover on nest survival of urban birds
Miles E. Becker and Peter J. Weisberg

Abstract
Climate change has the potential to influence avian population dynamics through nest-fate sensitivity to temperatures during the breeding season. Nest fate also varies across spatially heterogeneous habitat, and changing land uses may independently introduce stressors on reproductive outcome. Identifying the individual and synergistic effects of climate change and land-use change is necessary for understanding the impact of global change on native species. We studied the nest fate of 3 sympatric species breeding in urban habitat in an arid region of the western United States. We monitored nests (n = 371) of American Robin (Turdus migratorius), Mourning Dove (Zenaida macroura), and Black-headed Grosbeak (Pheucticus melanocephalus) over 4 yr on an urban-to-rural gradient and analyzed nest fate in relation to temperatures at the time of egg laying and after eggs hatched. Habitat measurements included nest height and the amounts of canopy cover and impervious surfaces at 3 spatial scales of 20-m, 100-m, and 500-m radii from the nest. Our data most strongly supported models that included temperature deviation after hatching, nest stage, fine-scale canopy cover, and pedestrian traffic. Nest survival increased at slight temperature increases during the nestling stage, which suggests that in a climate-change context, moderate warming in spring temperatures may be beneficial for some breeding birds. Nests were more likely to survive at locations with more canopy cover in a 20-m radius and at sites with more pedestrian traffic, which suggests that increasing cover of native riparian tree canopy at fine scales may enhance habitat quality in multiuse urban reserves. Our results demonstrate that effects of climate change on avian populations must be considered synergistically with land-use and land-cover characteristics of the urban landscape, including tree canopy cover and level of human disturbance.


Breeding biology of two endangered forest birds on the island of Kauai, Hawaii
Ruby L. Hammond, Lisa H. Crampton, and Jeffrey T. Foster

Abstract
Two forest bird species endemic to the island of Kauai in the Hawaiian Archipelago were listed under the U.S. Endangered Species Act in 2010 due to recent population declines. This research represents the first comprehensive breeding biology study of both species, the ‘Akikiki or Kauai Creeper (Oreomystis bairdi) and ‘Akeke‘e or Akekee (Loxops caeruleirostris). The 2-year study was initiated in 2012 to determine if low nesting success may be a cause of their population declines. We monitored 20 ‘Akikiki and 8 ‘Akeke‘e nests to assess basic nesting biology parameters (e.g., brood size; nest height; length of construction, incubation, and nestling periods) and to derive estimates of nesting success and investigate causes of failure. In general, ‘Akikiki and ‘Akeke‘e breeding biology was similar to other insectivorous Hawaiian honeycreepers. Mean nest height for ‘Akikiki and ‘Akeke‘e was high (9.2 ± 2.3 m SD and 11.1 ± 2.3 m SD, respectively) compared to most Kauai forest birds. Nesting success, calculated using program MARK, was 0.77 ± 0.12 SE for ‘Akikiki and 0.71 ± 0.17 SE for ‘Akeke‘e. Three ‘Akikiki and 2 ‘Akeke‘e nests failed. One ‘Akikiki nest failed due to nest predation and the other 2 to unknown causes. One ‘Akeke‘e nest failed due to poor nest attendance and the other to hatching failure. Nest sample sizes were small and should be considered with caution; however, these results suggest that low nesting success may not be a primary cause of decline in these species. Future research on both species should assess post-fledging, juvenile, and adult survival as potential causes of their populations' declines. Determining which demographic parameters currently have the largest negative impact on these populations is imperative for guiding effective management actions to conserve these species.


Habitat influences Northern Bobwhite survival at fine spatiotemporal scales
Adam K. Janke, Robert J. Gates, and Theron M. Terhune II

Abstract
Habitat quality influences individual survival at widely varying spatial and temporal scales. Understanding interactions between habitat and survival among individuals in declining populations that occupy highly modified landscapes can inform conservation strategies aimed at improving survival and population growth. We used radiotelemetry to monitor space use and daily survival of wintering Northern Bobwhites (Colinus virginianus) at the northern end of their range to test for fine spatial- and temporal-scale relationships between individual survival and habitat composition around radio-locations in agricultural landscapes in Ohio, USA. Habitat composition within daily and seasonal movement ranges of individuals (n = 189) during periods without snow cover did not explain variation in daily survival rates. However, mortality increased substantially in the presence of snow cover, and availability of woody cover and row crops within 95 m of an individual radio-location were positively associated with daily survival during those periods. A similar relationship between row crop availability and survival was supported at a larger scale that reflected composition of seasonal ranges (300-m buffer) but was less influential than fine-scale influences of woody cover and row crops. Our results suggest that previously documented selection for woody cover in our agricultural study areas was an adaptive behavior to improve individual survival during periods of snow cover. Positive associations between survival and row crop cover at daily and seasonal range scales suggest that agricultural landscapes confer improved survival probabilities when underlying constraints on occupancy related to woody cover are met. Collectively, our results suggest that targeted conservation practices focused on provision of suitable woody cover in agricultural landscapes in the northern end of the Northern Bobwhite's range has potential to improve winter survival and perhaps abate long-term population declines in the region.


Structure of avian assemblages in grasslands associated with cattle ranching and soybean agriculture in the Uruguayan savanna ecoregion of Brazil and Uruguay
Thaiane Weinert da Silva, Graziela Dotta, and Carla Suertegaray Fontana

Abstract
Conversion of grasslands into crops is a major factor leading to the decline of grassland birds. Cattle ranching represents another disturbance to natural grasslands, but may be less detrimental to grassland birds. We studied the diversity, density, and composition of bird species in Brazilian and Uruguayan grasslands under two different land use types: cattle ranching on seminatural grasslands, and soybean fields with interspersed patches of grassland. Cattle sites had higher species richness (n = 75 species) than soybean sites (n = 57 species). Most birds showed higher densities in cattle sites, but some common and habitat-generalist species were more abundant in soybean sites. Species composition did not differ significantly with land use. The generalist Eared Dove (Zenaida auriculata), however, was strongly associated with soybean sites. Among species of conservation interest, either regionally or globally, all had higher densities in cattle sites, highlighting the importance of maintaining these ranching areas. The persistence of grassland birds in soybean fields may be related to the presence of seminatural grassland patches within soybean crops.


Oil and natural gas development has mixed effects on the density and reproductive success of grassland songbirds
Sarah M. Ludlow, R. Mark Brigham, and Stephen K. Davis

Abstract
Oil and natural gas development has increased dramatically in native grasslands over the past 25 years. Some grassland songbirds are less abundant in areas with oil and gas development, but the effects vary among species and geographically within a species' range. The reproductive consequences of nesting in areas with oil and gas development are unknown. We assessed how the density and reproductive success of five species of grassland songbird in Alberta, Canada, varied with distance to oil and gas wells, gravel roads, and trails, and cover of crested wheatgrass (Agropyron cristatum), an aggressive alien plant that often becomes established following anthropogenic disturbance. Crested wheatgrass cover had the greatest impact on the grassland songbird community. Sprague's Pipit (Anthus spragueii) nest survival decreased as the amount of crested wheatgrass increased. As crested wheatgrass cover increased from 0% to 60%, density of Savannah Sparrows (Passerculus sandwichensis) declined by 50%, but they fledged 25% more young from successful nests. Density of Savannah Sparrows was twice as high near wells, and fledging success was 40% higher compared with 700 m away. Distance to gravel roads did not influence the density or reproductive success of any species. Sprague's Pipits and Baird's Sparrows (Ammodramus bairdii) avoided nesting within 100 m of trails, and both species fledged fewer young from successful nests near trails. In contrast, Vesper Sparrows (Pooecetes gramineus) nested close to trails and fledged more young from successful nests near trails. Western Meadowlarks (Sturnella neglecta) were not strongly affected by any variable. Brown-headed Cowbird (Molothrus ater) abundance was three times higher in study plots with wells, although we detected no associated increase in brood parasitism. Our results indicate that the introduction and spread of crested wheatgrass and the creation of access trails to well pads have negative reproductive consequences for primary endemic species such as Sprague's Pipit and Baird's Sparrow, although these results do not extend to other grassland birds. The spread of crested wheatgrass and the disturbance of access trails could be reduced by directional drilling of multiple wells from a single well pad.


COMMENTARY

Genetics, morphology, and ecological niche modeling do not support the subspecies status of the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus)
Robert M. Zink

Abstract
The Willow Flycatcher (Empidonax traillii) breeds throughout much of the United States, northwestern Mexico, and southeastern and southwestern Canada. A subspecies found in the southwestern United States and northwestern Mexico, E. t. extimus (Southwestern Willow Flycatcher), is listed as endangered under the U.S. Endangered Species Act (ESA). This subspecies was described in 1948, based on comparisons of a few external morphological characters from an unstated number of specimens and localities, although it was excluded from the last official list of subspecies by the American Ornithologists' Union. Like most avian subspecies, its validity has not been tested with modern morphological or genetic methods. Recent assessments of the subspecies have assumed it to be a distinct taxon, and some authors have limited their comparisons to E. t. extimus versus E. t. adastus (the subspecies immediately to the north of E. t. extimus), excluding comparison to western (E. t. brewsteri) and eastern (E. t. traillii) subspecies. To test subspecies limits, I reanalyzed available quantitative data on plumage coloration, and genetic variation in mitochondrial DNA and nuclear loci, and found no support for the distinctiveness of the Southwestern Willow Flycatcher. A test of niche divergence suggested that the Southwestern Willow Flycatcher does not have a significantly different climatic niche from its nearest geographic neighbor, E. t. adastus. I suggest that the Willow Flycatchers of the Southwest represent peripheral populations of an otherwise widespread species that do not merit subspecific recognition, and are therefore inappropriately listed as endangered under the ESA.


RESEARCH ARTICLES

Distance sampling survey and abundance estimation of the critically endangered Grenada Dove (Leptotila wellsi) 
Frank F. Rivera-Milán, Paulo Bertuol, Fernando Simal, and Bonnie L. Rusk

Abstract
The Grenada Dove (Leptotila wellsi) is critically endangered; its abundance, as estimated by territory mapping, ranges from 68 to 91 calling males (or 136–182 individuals, assuming a census of paired males). However, an accurate census is unlikely in dry and moist forests, unpaired males may be more detectable than paired males, and sex ratio may be male biased. Because methodology can limit the value of monitoring, we used a systematic grid of survey points and distance sampling to estimate abundance (density and population size), accounting for covariates that may influence detection. Time of day was the most important covariate (e.g., individuals were detected at larger distances early than late in the morning). Density was negatively influenced by disturbance level (deforestation) and positively influenced by food abundance and vegetation cover (leguminous trees). None of the covariates caused extreme heterogeneity; and conventional and multiple-covariate analyses generated similar detection and density estimates, which suggests that model selection was of secondary importance for abundance inferences. Detection probability (mean ± SE) was 0.166 ± 0.031 (95% confidence interval [CI]: 0.114–0.242) within 340 m, density was 0.021 ± 0.004 individuals ha−1 (95% CI: 0.014–0.030), and population size was 160 ± 30 individuals (95% CI: 107–229) in 7,621 ha. Although spatial distribution was slightly clumped (dispersion parameter: b̂∼1.31), we recommend surveying 150 points twice between late July and early August for abundance coefficient of variation (CV) ≤0.15, even if spatial distribution becomes more clumped (e.g., b = 2.5). More survey data are needed to better understand spatial and temporal density variation, test hypotheses about survey design (e.g., road bias in density estimation) and Grenada Dove ecology (rainfall, food, cover, and density correlations), and evaluate management actions (predator removal in nesting areas). With <250 Grenada Doves in the survey region, our data highlight the precarious conservation status of this island endemic, and the urgent need for effective management and targeted monitoring.


Anthropogenic activities influence the abandonment of Bearded Vulture (Gypaetus barbatus) territories in southern Africa 
Sonja C. Krüger, Robert E. Simmons, and Arjun Amar

Abstract
Developing an effective conservation strategy for a critically endangered species relies on identifying the most pressing threats to the species. One approach to elucidate these threats for a long-lived animal with high territorial fidelity is to identify factors associated with territorial abandonment. The Bearded Vulture (Gypaetus barbatus) has declined dramatically in southern Africa over the past few decades, with nearly 50% of known territories being abandoned. In this study we examine the evidence for 3 hypotheses: that territorial abandonment was associated with (1) human impact, (2) food availability, or (3) climate change, or a combination of these. Model selection was used to determine the relative importance of 7 covariates within the home range of an adult pair, an area of 10 km radius (314 km2) around each nest. Our analyses provided strongest support for the human impact hypothesis, with abandonment more likely in territories with more power lines and higher densities of human settlements. Additionally, within Lesotho, southern Africa, there was some support for the food shortage hypothesis, with territories more likely to have remained occupied where they had a greater number of feeding sites within close proximity. Our data provided no support for the hypothesis that climate change may be driving abandonment through a direct impact of elevation or nest site aspect. Our results are in accordance with the main causes of mortality: poisoning and power line collisions. We suggest that conservation measures should focus on limiting the development of further human settlements and power lines within 10 km of occupied territories, applying mitigation measures to existing power lines and increasing law enforcement and education in areas still occupied by the species.


A century of change in Glaucous-winged Gull (Larus glaucescens) populations in a dynamic coastal environment
Louise K. Blight, Mark C. Drever, and Peter Arcese

Abstract
As conspicuous midtrophic omnivores, gulls can serve as useful indicators to characterize long-term ecological changes in marine ecosystems. Glaucous-winged Gulls (Larus glaucescens) have been studied in the Georgia Basin of British Columbia, Canada, an urbanized coastal zone, since the late 1800s. We collated all available information to develop a (noncontinuous) 111-year time series of counts at breeding colonies, and combined these counts with demographic vital rates to assess how changes in historical gull egg harvesting practices, forage fish abundance, and Bald Eagle (Haliaeetus leucocephalus) numbers affected gull population trajectories from 1900 to 2010. Mean counts at 87 breeding colonies in the Georgia Basin showed a nonlinear trend, increasing from historical low counts in the early part of the twentieth century to peak values in the 1980s, and declining thereafter to the end of the time series. Demographic models that integrated temporal trends in clutch size and nesting success, and which also included a food-related decline in first-year survival or a further reduction in nesting success as a function of eagle abundance, successfully reproduced trajectories of gull population growth rates over the study period. Glaucous-winged Gulls have thus responded to a series of changes in the Georgia Basin. These patterns are consistent with population release following cessation of egg harvesting; growing reliance by gulls on nonfish foods and resulting declines in clutch size, productivity, and first-year survival; and the effects of recovering Bald Eagle populations. These results highlight the value of compiling data from multiple retrospective studies to better understand the complex factors affecting long-term trends in animal populations.


Nest visits and capture events affect breeding success of Yellow-billed and Pacific loons 
Brian D. Uher-Koch, Joel A. Schmutz, and Kenneth G. Wright

Abstract
Accurate estimates of breeding success are essential for understanding population dynamics and for managing populations. Unfortunately, research activities to collect these data can negatively impact the breeding success of the study species and bias estimates of breeding success. Despite the potential for negative impacts, few studies have documented the effect of capturing incubating adults on nest survival or compared nest survival following different capture methods. In this study we evaluate the impacts of investigator disturbance associated with captures and nest visits on nest survival of Yellow-billed Loons (Gavia adamsii) and Pacific Loons (Gavia pacifica) in the National Petroleum Reserve-Alaska (NPR-A), an area of conservation concern, in 2011–2013. In an effort to reduce capture-related nest failures, we developed a new suspended dive net technique to catch territorial aquatic birds while off their nests. We then compared nest survival following suspended dive net captures to bow-net trap captures of breeding adult loons. Daily nest survival following bow-net trap or suspended dive net capture was about 30% lower than when adults were not captured. The effect of captures on nest survival was similar between bow-net trap and suspended dive net capture methods. Nest visits without captures also negatively impacted nest survival, although less than captures. If not accounted for, nest visitation biased daily survival rates of nests downward 6%. Effects of investigator disturbance did not differ by species or between years. Our results suggest that any source of disturbance that displaces incubating adult loons could potentially reduce nest survival. To maximize breeding success, human disturbance factors should be limited near loon nests.

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