Cattle grazing in CRP grasslands during the nesting season: effects on avian reproduction

Bird populations in grasslands have experienced declines coinciding with loss and fragmentation of prairies. The United States Department of Agriculture (USDA)-administered Conservation Reserve Program (CRP) is the most extensive grassland restoration program in North America and it has especially benefitted grassland birds. Grazing by domestic cattle has been restricted in CRP during avian nesting seasons despite the potential improvements in structuring habitat for a greater diversity of grassland bird species. Potential negative consequences of grazing in CRP grasslands include trampling of nests by cattle, reductions in nest concealment from predators, and attraction of brood-parasitic brown-headed cowbirds (Molothrus ater). We designed an experiment to test for effects of cattle grazing in CRP fields during the nesting season on nest survival and brood parasitism of 5 bird species that commonly nest in CRP grasslands: mourning dove (Zenaida macroura), grasshopper sparrow (Ammodramus savannarum), dickcissel (Spiza americana), and eastern (Sturnella magna) and western (S. neglecta) meadowlarks. Grazing was implemented during summers 2017 and 2018 on 17 of 36 fields followed by a year of rest on all fields in 2019. Of the 879 nests on grazed fields, only 4 were likely trampled by cattle (vs. 54% of all nests estimated as failing because of depredation). Experimental grazing (grazed vs. ungrazed fields) had variable effects on nest survival and cowbird parasitism among the bird species analyzed. Negative effects of grazing on daily nest survival of dickcissel and meadowlarks were apparent, at least in some years. We found no direct effects of grazing on nest survival of mourning dove or grasshopper sparrow. Probability and intensity (cowbird offspring/nest) of cowbird parasitism in dickcissel nests was higher on grazed versus ungrazed sites but only in conservation practice (CP) CP2 (vs. CP25 fields). Parasitism probability of grasshopper sparrow nests by cowbirds was higher on grazed fields in the 2 years after introduction of cattle in 2017. Greater vegetative concealment around nest sites was associated with reduced cowbird parasitism of meadowlark and grasshopper sparrow nests and higher nest survival for grasshopper sparrows. Reductions in vegetative height caused by longer-term or high-intensity grazing might therefore have negative consequences for some grassland birds by increasing nest site visibility and exposure to cowbird parasitism. Our results indicate that cattle grazing in CRP fields during the nesting season might have some negative effects on reproductive success of some grassland bird species, at least in the short term; however, the potential improvements of structuring habitat to accommodate more grassland bird species and increasing landowner participation in the CRP are considerable.     

Factors Affecting Songbird Nest Survival in Northern Mixed-Grass Prairie

ABSTRACT Factors associated with the nest survival of mixed-grass prairie passerines are not well known, especially in the context of contemporary grassland management. We documented the nest survival of clay-colored sparrows (Spizella pallida), savannah sparrows (Passerculus sandwichensis), and bobolinks (Dolichonyx oryzivorus) in managed prairie in northwestern North Dakota, USA. We used logistic exposure models and an information-theoretic framework to estimate nest survival and evaluate support for mechanisms (grazing, temporal factors, nest parasitism, nest-site vegetation, and nest-patch factors) relevant to nest survival. Survival for the entire nesting interval (23–28 days) was low for clay-colored sparrow (18.2%), savannah sparrow (15.5%), and bobolink (3.5%). We found support for a cubic effect of nest age; survival of savannah and clay-colored sparrow nests was greatest during mid-incubation and least during the mid-nestling period. Parasitized clay-colored sparrow and bobolink nests had greater survival rates than nonparasitized nests. Nest survival of clay-colored sparrows increased with increasing vegetation height and density. For savannah sparrows, nest survival was lower when cattle were present than when cattle were absent. Characteristics of the nest patch did not have strong effects based on model coefficients and confidence intervals, though they appeared in many of the most supported models. Positive effects of vegetation height and density on nest survival of clay-colored sparrows and negative effects of cattle presence on nest survival of savannah sparrows suggest some detrimental effects of grazing. However, the need to restore and maintain intact prairies likely warrants the continuation of cattle grazing on conservation lands.     

Grassland birds and rotational-grazing in the northeast: Breeding ecology,survival and management opportunities

We studied long-term (2002–2009) demographics of bobolinks (Dolichonyx oryzivorus) and savannah sparrows (Passerculus sandwichensis) breeding in rotationally grazed systems in the northeastern United States. Both nest success (6–44% bobolink; 7–48% savannah sparrow) and annual productivity (0.43–2.83 bobolink; 0.70–2.35 savannah sparrow) varied annually. Predation (48%) and trampling by cows (32%) accounted for most failed nests. Annual adult apparent survival ranged from 23% to 85% and showed substantial variation by species and sex. Although grazing resulted in substantial loss of vegetative cover, savannah sparrows responded similarly to predation and grazing-induced nest failure (time to renest, distance moved between nests) and generally remained in the same paddock to renest. Minimum paddock size to accommodate one female within this rotation was 70 m × 70 m (0.49 ha), allowing a female to stay within a paddock and move (approx. 50 m) between nesting attempts. To balance pasturing objectives and birds' needs in paddocks first grazed before 25 June, managers in the Northeast should rest that paddock 42–50 days before the second grazing. © 2011 The Wildlife Society.     

Wild Turkey Nest Success in Pine-Dominated Forests of the Southeastern United States

Nest success is a primary component of productivity for wild turkeys (Meleagris gallopavo; turkeys) and there is concern that turkey productivity is declining across the southeastern United States. We evaluated the influence of nest site and landscape characteristics on risk of nest failure for turkeys in pine (Pinus spp.)-dominated forests across the southeastern United States. We used Cox proportional hazard models to evaluate daily hazard of nest failure associated with nest site and landscape metrics within 500-m and 1-km buffers centered on nests. Of 451 nests monitored (n = 320 females) between 2014 and 2018, 76% failed, with predation as the primary cause. Daily hazard of nest failure increased by 1.2% for each day that females delayed nest incubation following the mean nesting date (29 Apr; β_day = 0.010 ± 0.002 [SE]; hazard ratio [HR] = 1.01, 95% CI = 1.006–1.015). Environmental covariates associated with risk of nest failure included the maximum enhanced vegetation index (EVI) and distance to the nearest ecotone. Daily hazard increased with increasing distance away from an ecotone (β_ecotone = 0.16 ± 0.06; HR = 1.17, CI = 1.03–1.32) and with lower EVI around the nest (β_EVI = −0.30 ± 0.06; HR = 0.74, CI = 0.65–0.83). Additional nest site or landscape covariates were included in competitive models but did not influence risk of nest failure significantly. Our study highlights the importance of considering landscape context when designing and implementing land management actions intended to enhance wild turkey reproduction. Our findings suggest that landscape metrics thought to be important to turkeys in northern agro-forested landscapes may not be relevant to turkeys in pine ecosystems of the southeastern United States. © 2021 The Wildlife Society.     

Effects of fire and grazing on grasshopper sparrow nest survival

Patch-burn grazing is a management framework designed to promote heterogeneity in grasslands, creating more diverse grassland structure to accommodate the habitat requirements of many grassland species, particularly grassland birds. Published studies on the effects of patch-burn grazing on passerines have been conducted on relatively large (430–980 ha pastures), contiguous grasslands, and only 1 of these studies has investigated the reproductive success of grassland birds. We assessed the effects of the patch-burn grazing and a more traditional treatment on the nesting ecology of grasshopper sparrows (Ammodramus savannarum) in small (<37 ha pastures) grasslands located in southern Iowa from May to August of 2008 and 2009. The study pastures were grazed from May to September and prescribed burns were conducted in the spring. We investigated the effects of treatments on clutch size and modeled grasshopper sparrow nest survival as a function of multiple biological and ecological factors. We found no difference in clutch size between treatments; however, we did find a reduction in clutch size for nests that were parasitized by brown-headed cowbirds (Molothrus ater). Constant daily survival rates were greater in patch-burn grazed pastures than in grazed-and-burned pastures (patch-burn grazed rate and grazed-and-burned rate ). Competitive survival models included year, stage of nest, nest age, and cool-season grass (csg) abundance within 5 m of the nest. Overall, csg abundance had the greatest effect on survival and had a negative influence. Although survival rates were highest in patch-burn grazed pastures, multiple factors influenced grasshopper sparrow survival. Nest survival rates for both treatments were relatively low, and variables other than treatment were more instrumental in predicting grasshopper sparrow survival. We recommend decreasing overall vegetation cover if increasing nesting habitat for grasshopper sparrows is a management goal. In addition, we recommend further investigation of heterogeneity management in fragmented landscapes to better understand how it affects biodiversity in relatively small management units that typify grassland habitats in the Midwest. © 2011 The Wildlife Society.     

Conservation Reserve Program Benefits on Henslow's Sparrows Within the United States

ABSTRACT Henslow's sparrow (Ammodramus henslowii) is one of North America's fastest declining songbirds. Population declines combined with a small global population have led to heightened conservation concern. I used data from the North American Breeding Bird Survey to assess the impact that the Conservation Reserve Program (CRP) has had on Henslow's sparrows throughout their United States breeding range. My analysis suggests local Henslow's sparrow population trends are correlated with CRP enrollment, with populations increasing more in areas with relatively high local CRP enrollment, and that CRP appears to be playing a significant role in reversing long-term population declines.     

Extrinsic and intrinsic factors influence fitness in an avian hybrid zone

The effects of hybridization on evolutionary processes are primarily determined by the differential between hybrid and parental species fitness. Assessing the impacts of hybridization can be challenging, however, as determining the relationship between individual fitness and the extent of introgression in wild populations is difficult. We evaluated the fitness consequences of hybridization for pure and hybrid females in a hybrid zone between two tidal marsh birds, the saltmarsh sparrow (Ammodramus caudacutus), a salt marsh obligate, and Nelson's sparrow (A. nelsoni), which has a broader ecological niche and a much younger evolutionary association with salt marshes. Biotic stressors associated with nesting in tidal environments suggest an important role for differential adaptation in shaping hybrid zone dynamics, with saltmarsh sparrows predicted to be better adapted to nesting in salt marshes. We collected DNA samples from adults (n = 394) and nestlings (n = 431) to determine the extent of introgression using 12 microsatellite loci and tested for the influence of extrinsic (nest placement) and intrinsic (genotype) factors on female reproductive success. We monitored nests (n = 228), collected data on reproductive output, and estimated daily nest survival rates using female genotype and nest characteristics as covariates. To test for reduced survival of hybrid females, we also used capture data to assess the distribution of admixed male and female individuals across age classes. Reproductive success of females varied by genotypic class, but hybrids did not have intermediate success as predicted. Instead, we found that pure Nelson's sparrows had, on average, 33% lower hatching success than any other genotype, whereas F1/F2 hybrids, backcrossed Nelson's sparrows, and backcrossed and pure saltmarsh sparrows all had similar hatching success. We found no effect of genotype or nest placement on daily nest survival probabilities. However, hybrid individuals with a higher proportion of saltmarsh sparrow alleles exhibit nesting behaviours better suited to nesting successfully in tidal marshes. Further, while the proportion of F1/F2 individuals was similar between nestling and adult males, we found that the proportion of F1/F2 individuals was 2.3 times greater in nestling females compared with adult females, indicating reduced survival of F1 females. We conclude that differences in reproductive success among pure and admixed individuals coupled with intrinsic mechanisms (reduced survival in F1 females) shape hybrid zone dynamics in this system.     

GRASSLAND BIRDS NESTING IN HAYLANDS OF SOUTHERN SASKATCHEWAN: LANDSCAPE INFLUENCES AND CONSERVATION PRIORITIES

Abstract: To determine the benefits to grassland birds of converting cropland to hayland in southern Saskatchewan, Canada, we quantified the relative nest abundance and success of grassland nesting birds in haylands and the influence landscape variables have on these parameters. We found nests of 26 species of grassland nesting birds, primarily waterfowl and vesper sparrow (Pooecetes gramineus). With the exception of the northern pintail (Anas acuta), few nesting attempts were recorded for species of high priority in the Prairie Pothole Bird Conservation Region. Mayfield nest success for all waterfowl (20 and 13% in 1999 and 2000, respectively) was high relative to previously reported nest success estimates in other habitat types—especially spring-seeded cropland—and was near levels thought to be required to sustain populations (15–20%). Vesper sparrow nest success (39 and 33% in 1999 and 2000, respectively) also was high relative to that reported in other studies. Haying destroyed few nests as wet weather delayed operations in 1999 and 2000. More nests may be destroyed by haying in other years as approximately 25% of nests in this study were still active on the long-term average haying date for southern Saskatchewan. Among models we developed to explain waterfowl relative nest abundance, amount of cropland in the surrounding landscape and field area were the most informative. Evidence that a specific set of landscape variables was important to models of waterfowl nest success was equivocal. Landscape variables did not explain variation in vesper sparrow relative nest abundance or nest success. Within our study area, conversion of cropland to hayland appears to provide significant benefits to a variety of grassland species, including some species of high conservation priority (e.g., northern pintail). Grassland species of conservation concern nested less frequently in hayland than in native grassland.     

Factors affecting piping plover hatching success on Long Island,New York

Low hatching success may limit progress towards reaching productivity goals for Atlantic Coast piping plover (Charadrius melodus) recovery, despite management strategies to protect eggs from predators and decrease human disturbance of birds on nests. We measured piping plover hatching success on Eastern Long Island beaches and identified the major causes of egg failure to better understand why eggs that were otherwise intact (not depredated or destroyed by tidal flooding) failed to hatch. We documented egg and nest fates, dissected contents of unhatched eggs to determine viability, and recorded human and predator activity near a subset of plover nests on Suffolk County Parks properties. The low hatching success we recorded (0.60) in 2006 and 2007 would require higher chick survival rates than are typically observed for piping plovers to meet recovery targets for productivity. Few eggs showed signs of poor viability and overall egg hatchability was comparable to other ground nesting birds. Most egg failure was due to either depredation at unexclosed nests or nest abandonment by adults. The best predictor of nest abandonment was the maximum number of red fox tracks (Vulpes vulpes) counted on nearby transects (β = −1.16, 95% CI: −2.0 to −0.3) and we found evidence that plovers abandoned eggs in response to predation risk (e.g., a fox circling a nest exclosure). Adults from abandoned nests may have deserted eggs or been depredated. In either case, intact and viable eggs were abandoned. Nest abandonment was not related to human activity near nests, which were buffered from human disturbance by symbolic string fencing. Our results suggest that depredation and nest abandonment (e.g., desertion or death of adults) due to predator disturbance, not human disturbance or poor egg viability, contributed to the low hatching success we recorded. Active predator removal in addition to modification of predator exclosure use and design may be necessary to prevent direct (egg depredation) and indirect (nest abandonment) negative effects of predators on hatching success. © 2010 The Wildlife Society.     

Habitat and landscape effects on abundance of Missouri's grassland birds

Of 6 million ha of prairie that once covered northern and western Missouri, <36,500 ha remain, with planted, managed, and restored grasslands comprising most contemporary grasslands. Most grasslands are used as pasture or hayfields. Native grasses largely have been replaced by fescue (Festuca spp.) on most private lands (almost 7 million ha). Previously cropped fields set aside under the Conservation Reserve Program (CRP) varied from a mix of cool-season grasses and forbs, or mix of native warm-season grasses and forbs, to simple tall-grass monocultures. We used generalized linear mixed models and distance sampling to assess abundance of 8 species of breeding grassland birds on 6 grassland types commonly associated with farm practices in Missouri and located in landscapes managed for grassland-bird conservation. We selected Bird Conservation Areas (BCAs) for their high percentage of grasslands and grassland-bird species, and for <5% forest cover. We used an information-theoretic approach to assess the relationship between bird abundance and 6 grassland types, 3 measures of vegetative structure, and 2 landscape variables (% grassland and edge density within a 1-km radius). We found support for all 3 levels of model parameters, although there was less support for landscape than vegetation structure effects likely because we studied high-percentage-grassland landscapes (BCAs). Henslow's sparrow (Ammodramus henslowii) counts increased with greater percentage of grassland, vegetation height-density, litter depth, and shrub cover and lower edge density. Henslow's sparrow counts were greatest in hayed native prairie. Dickcissel (Spiza americana) counts increased with greater vegetation height-density and were greatest in planted CRP grasslands. Grasshopper sparrow (A. savannarum) counts increased with lower vegetation height, litter depth, and shrub cover. Based on distance modeling, breeding densities of Henslow's sparrow, dickcissel, and grasshopper sparrow in the 6 grassland types ranged 0.9–2.6, 1.4–3.2, and 0.1–1.5 birds/ha, respectively. We suggest different grassland types and structures (vegetation height, litter depth, shrub cover) are needed to support priority grassland-bird species in Missouri. © 2011 The Wildlife Society.     

Evaluation of the Umbrella Species Concept at Fine Spatial Scales

Declines in the spatial extent of the sagebrush ecosystem have prompted the consideration of conservation efforts that view the greater sage-grouse (Centrocercus urophasianus; sage-grouse) as an umbrella species at landscape scales. Conservation strategies that focus on an umbrella species, however, may have unintended negative consequences for co-occurring species at finer scales. In North America, grassland and shrubland songbird populations are declining faster than other avian groups. Conservation of sage-grouse habitats may protect songbird habitats where distributions overlap. To assess the umbrella species concept at fine scales, we quantified nest-site selection for a sagebrush-obligate songbird, the Brewer's sparrow (Spizella breweri). We then compared the fine-scale habitat variables that influenced Brewer's sparrow nest-site selection with fine-scale nest-site selection for sage-grouse in the Powder River Basin region of northeastern Wyoming, USA. We modeled nest-site selection using conditional logistic regression for Brewer's sparrow (2016–2017) and logistic regression for sage-grouse (2004–2007). Both species selected nest sites with higher visual obstruction, shrub height, and branching density, although the selection for higher shrub height was stronger for sage-grouse. Brewer's sparrows selected nest shrubs with higher percentage of living foliage (vigor), and the opposite was shown for sage-grouse. At the nest site, based on the variables we measured, our results suggest that Brewer's sparrows and sage-grouse select for similar habitat attributes, with the exception of shrub vigor of the nest shrub. The stronger selection for more vigorous shrubs in Brewer's sparrows may be because they nest in shrubs, rather than on the ground under shrubs (as in sage-grouse). Most of the conservation objectives for protection of sage-grouse habitats appear to be beneficial or inconsequential for Brewer's sparrow. Local habitat management for sage-grouse as a proxy for conservation of other species may be justified if the microhabitat preferences of the species under the umbrella are understood to avoid unintentional negative effects. © 2019 The Wildlife Society.     

Black-capped vireo nest predator assemblage and predictors for nest predation

Nest predation is a major limiting factor for songbird productivity, including the federally endangered black-capped vireo (Vireo atricapilla). However, nest predator information is limited across the range of the black-capped vireo in central and southwest Texas. We monitored nests in 3 counties within the breeding range of black-capped vireos in Texas in 2008 and 2009 and used continuous recording digital video cameras to record predation events. We video-monitored 115 nests and documented 39 predation events by at least 9 predator species. Overall, we observed avian species (51%, n = 39), specifically brown-headed cowbirds (Molothrus ater; n = 12), and snakes (26%, n = 39) as the most frequent nest predators. The estimated daily nest survival rate during the laying and incubation stage was 0.985 (95% CI = 0.967–0.993) and 0.944 (95% CI = 0.921–0.961) during the nestling stage. In addition, we analyzed models of predator-specific nest predation using multinomial logistic regression. Effect of nest height on predation rate was significant for snakes; nest stage was significant for nests depredated by avian predators. By identifying and increasing our knowledge of nest predators and vegetation characteristics associated with greater risk of predation in multiple locations within the black-capped vireo's range, we can effectively manage habitat to benefit recovery efforts of the species. © 2012 The Wildlife Society.     

Evidence for a Recent Henslow's Sparrow Population Increase in Illinois

Abstract: The Henslow's sparrow (Ammodramus henslowii) is a species of high conservation concern due to long-term population declines and a small global population. Habitat loss is considered to be the most likely cause of Henslow's sparrow declines and the recent establishment of large acreages of undisturbed grasslands through the Conservation Reserve Program is considered to have the potential to benefit populations. I used data from Illinois' Spring Bird Count to estimate recent population trends and examine the association that changes in land-use, especially the establishment of Conservation Reserve Program lands, have had on local Henslow's sparrow population trends. My analysis shows that Henslow's sparrow populations have increased substantially within Illinois, USA over the last 10 years and that this population increase strongly coincides with the establishment of >400,000 ha of grasslands within the state by the Conservation Reserve Program. New rules allowing for managed haying and grazing on Conservation Reserve Program grasslands have the potential to reduce the suitability of program fields for this species and, thus, Henslow's sparrow use of program fields should be monitored as the new rules are implemented.     

Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats,Alaska

Abstract: Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands >10 ha, small wetlands <10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood-rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.     

Merriam's Turkey Nest Survival and Factors Affecting Nest Predation by Mammals

Abstract: Nest success is an important parameter affecting population fluctuations of wild turkeys (Meleagris gallopavo). Factors influencing mammalian predation on turkey nests are complicated and not well understood. Therefore, we assessed nest hazard risk by testing competing hypotheses of Merriam's turkey (M. g. merriami) nest survival in a ponderosa pine (Pinus ponderosa) ecosystem during 2001–2003. We collected nesting information on 83 female Merriam's turkeys; annual nest success averaged 50% for adult females (range = 45–59%) and 83% for yearling females (range = 75–100%). Proportional hazard modeling indicated that precipitation increased the hazard of nest mortality. However, estimated hazard of nest predation was lowered when incubating females had greater shrub cover and visual obstruction around nests. Coyotes (Canis latrans) were the primary predator on turkey nests. We hypothesize that precipitation is the best predictor of nest survival for first nests because coyotes use olfaction effectively to find nesting females during wet periods. Temporally, as the nesting season progressed, precipitation declined and vegetation cover increased and coyotes may have more difficulty detecting nests under these conditions later in the nesting period. The interaction of concealment cover with precipitation indicated that nest hazard risk from daily precipitation was reduced with greater shrub cover. Management activities that promote greater shrub cover may partially offset the negative effects of greater precipitation events.     

Environmental conditions but not nest composition affect reproductive success in an urban bird

Adjusting the composition of their nests, breeding birds can influence the environmental conditions that eggs and offspring experience. Birds often use feathers to build nests, presumably due to their insulating properties. The amount of feathers in nests is often associated with increased nestling survival and body condition. However, it is unclear whether these putative beneficial effects of adding feathers to nests are relevant in a wide range of environmental conditions. Here, we combine data on weather conditions and feathers in nests (i.e., nest composition) to investigate their relative contribution to reproductive success in the Eurasian tree sparrow (Passer montanus). Specifically, we investigate whether the effect of weather conditions on breeding success is modulated by the amount of feathers added to the nest. We found a strong negative effect of rainfall on the number of nestlings that successfully fledged per breeding attempt, but this negative effect was not mitigated by the amount of feathers in nests. We also found that the amount of feathers in nests varied along the breeding season, with nests containing more feathers early in the breeding season, when temperatures were lower. Despite considerable variation in nest composition, our results do not suggest an important role of feathers in nests protecting eggs or nestling tree sparrows against fluctuations in environmental conditions.     

Ability to alter song in two grassland songbirds exposed to simulated anthropogenic noise is not related to pre-existing variability

Organisms encounter noise naturally in the environment. However, increasing prevalence of human-caused noise seems to be resulting in behavioural changes in many animals that can affect survival and reproduction. Not all species react the same way to noise; some adjust their vocal signals while others do not. We hypothesized that species with more variability in their vocal signals would be better able to adjust their signals to be audible over anthropogenic noise. We tested this within a large-scale manipulative experiment by recording songs of two grassland songbirds, Baird’s sparrow (Ammodramus bairdii) and Savannah sparrow (Passerculus sandwichensis), both of which are found in areas increasingly affected by energy extraction noise. We compared these species because Savannah sparrows have more variability in their songs geographically and temporally compared to Baird’s sparrows. We recorded both species’ songs before, during and after high-fidelity playbacks of oil well drilling noise. Surprisingly, both species changed parts of their songs in the presence of noise (Baird’s sparrow usually decreasing frequency and Savannah sparrow increasing frequency) and these changes were not related to seasonal, song, or syllable variability. We suggest instead that acoustically heterogeneous environments may favour the evolution of species that are capable of adjusting their songs in response to variable ambient noise.     

Is Carrying Feathers a Sexually Selected Trait in House Sparrows?

Males in several avian groups carry specialised materials as part of their courtship display. Females may vary their investment in reproduction in relation to their mates' attractiveness. The house sparrow (Passer domesticus) population on Dassen Island, South Africa, builds domed nests in the branches of trees. These nests are more or less spherical structures with a deep cup lined largely with feathers. When males collect feathers, they call to females and display the feather before it is added to the nest. We examined whether carrying feathers provides females with an index of male quality, which correlates with their subsequent investment in parental care. Additionally, we studied the potential importance of feathers in nest insulation. Feathers were collected mainly by males. Males also brought larger feathers, and deposited more feathers in nests, than females. Number of trips with feathers – which increased after feathers were experimentally removed from nests – and number of feathers brought varied among males. Volume of feathers influenced females' investment in reproduction and positively correlated with clutch size and chick feeding rates. We found more feathers during incubation and immediately after chicks hatched, when nest heat requirements peak. Furthermore, number of trips with feathers and number and size of feathers were greater during incubation. Our results suggest that this feather‐carrying behaviour by male house sparrows influences maternal reproduction investment and could be a kind of parental care per se by supplementing nest insulation.     

Effects of prescribed burning on avian nest survival in the southern Great Plains

Shrubs, such as mesquite (Prosopis spp.) and cholla (Opuntia spp.), now dominate fire-suppressed grasslands in southwestern North America. Responses of birds to prescribed burning of the shortgrass prairie in this region are poorly understood. We examined daily survival rates of mourning dove (Zenaida macroura) and lark sparrow (Chondestes grammacus) nests in an experimental landscape (4,811 ha) of spatially replicated, inter-annual fire frequencies (burning every 2 yr, 4 yr, or 10 yr) near Amarillo, Texas. Herbaceous habitat structure was most developed in infrequently burned plots, but shrub densities were less variable among the burn treatments. We modeled daily nest survival (DSR) against burn frequency, shrub density at nest sites, and nest stage (incubation or nestling). Daily survival of mourning dove nests was not well-related to any measured covariate, but lark sparrow DSR was negatively related to the duration of inter-annual burn frequency. In semiarid grasslands heavily inundated with shrubs, prescribed burning may positively influence the nest success of some bird species. © 2011 The Wildlife Society.     

MICROGEOGRAPHIC PATTERNS OF GENETIC AND MORPHOLOGICAL VARIATION IN SAVANNAH SPARROWS (PASSERCULUS SANDWICHENSIS)

Surveys of genetic population structure are often limited to large geographic scales because geographically close populations are indistinguishable. Genetic uniformity across adjacent demes can be interpreted as evidence for cohesion (panmixia) or recent divergence. However, poor genetic resolution at microgeographic scales can also arise from the use of overly conservative (slowly evolving) markers. This study examines the ability of hypervariable, minisatellite loci to discriminate among geographically close populations of Savannah sparrows (Passerculus sandwichensis) and to track morphological differentiation at a microgeographic scale (interregional distance < 55 km). Savannah sparrows breeding at five island and two mainland sites in the Bay of Fundy, New Brunswick, Canada, show concordant patterns of variation in external morphology (seven characters) and multilocus DNA fingerprinting profiles (S_xy): island sparrows are phenotypically larger and genetically more similar to each other than they are to mainland sparrows. This pattern of variation is consistent with both adaptive (natural selection) and nonadaptive (genetic drift) mechanisms of population divergence. Based on minisatellite diversity, the effective size of both island and mainland populations is 37, an estimate substantially lower than census population sizes. These data are discordant with observations of sparrow vagility and abundance and suggest a closer examination of microgeographic patterns in avian systems.