Subfossil remains indicate that the Laysan Duck (Anas laysanensis) formerly occurred throughout the Hawaiian archipelago, but for more than 150 years it has been confined to a single, small atoll in the northwestern chain, Laysan Island. In 2004–2005, 42 ducks were reintroduced from Laysan to Midway Atoll, where they exhibited variation in life history never observed on Laysan. On Laysan, females have never been observed to breed successfully at age 1 year and few attempt it, whereas on Midway, females routinely raised young at <1 year of age. Mean (± SD) clutch size on Midway (7.0 ± 1.1, n = 41) was larger than the maximum clutch size of six eggs observed on Laysan. On Midway, renesting following nest failure (0.55 probability, n = 27) and double brooding (0.50, n = 54) were routine, and two instances of triple brooding were observed, whereas on Laysan, renesting and double brooding are rare (0.05 probability for both during our study; n = 21 and 19, respectively) and triple brooding has never been observed. Other novel life history on Midway included early cessation of parental care to renest. Altered life history on Midway is likely related to better feeding conditions and low population density compared with Laysan. An especially intriguing possibility is that the phenotypic plasticity observed represents exposure of hidden reaction norms evolved when the species inhabited a range of environments, but several alternative explanations exist. Future reintroductions of this species may provide opportunities to test hypotheses about mechanisms underlying phenotypic plasticity.

Wetland habitats in the Prairie Pothole Region of North America have been greatly reduced since European settlement, but the availability of managed wetlands has increased. The relative efficacy of these two habitats for meeting energetic demands of migrating shorebirds is unknown. To assess the relative suitability of stopover sites, we measured plasma metabolites and creatine kinase in Least Sandpipers (Calidris minutilla), Semipalmated Sandpipers (C. pusilla), and Pectoral Sandpipers (C. melanotos) at natural and managed wetland sites during fall migration in northeastern South Dakota and westcentral Minnesota. We used stepwise multiple regression to identify significant effectors of plasma metabolite levels, followed by analysis of covariance to compare metabolite values between birds in the two habitat types. Plasma metabolite levels generally did not differ significantly between birds in the two habitat types, with two exceptions. Plasma triglycerides of Pectoral Sandpipers were 2.6× higher at managed than at natural wetlands, suggesting higher rates of fattening at managed sites, but this was not supported by plasma glycerol levels, which did not differ significantly between birds in the two habitat types, or by body mass, which was greater for adult males in natural wetlands. Plasma creatine kinase levels of Least Sandpipers were 75% higher at managed than at natural wetlands, which suggests that repair of flight-induced muscle damage may be slower for this species at managed wetlands. The general absence of significant differences in plasma metabolites among shorebirds in the two wetland types suggests that natural and managed wetlands serve as similarly effective stopover habitat for fall-migrating shorebirds in the Prairie Pothole Region.

Both baseline and stress-induced concentrations of corticosterone (CORT) vary seasonally in a predictable fashion in many wild birds. Hypotheses about why these patterns exist include the “behavior hypothesis,” which predicts that animals will down-regulate stress-induced CORT when CORT-induced behaviors are too likely to cause reproductive failure; and the “preparative hypothesis,” which posits that baseline and stress-induced CORT will both be high at times of year with a higher incidence of predictable stressors. We tested predictions made by the behavior and predictive hypotheses about the CORT sensitivity of tissues involved in breeding: whole brain, hippocampus, and gonads. We used radioligand binding assays to examine glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) binding in free-living House Sparrows (Passer domesticus) at several different life history stages. We found lowest GR binding in whole brain during breeding; this suggests relative insensitivity of brain tissue to CORT at this time of year, which is consistent with predictions made by the behavior hypothesis. We found highest GR binding in whole brain in the pre-egg-laying period, which is consistent with the preparative hypothesis, given that this life stage is associated with a predictable increase in the likelihood of stressful events such as threats to territory and nest sites. However, we found no seasonal changes in GR or MR binding in gonads or hippocampus. Our results suggest that down-regulation of brain GR could be one way birds limit the negative effects of CORT release on breeding behavior, but further studies are necessary to understand the anatomic specificity of these changes.

Past studies of the replacement rules for flight feathers of cuckoos have been plagued by the erroneous assumption that the primaries constituted a single molt series. Instead, we show that the primaries of the Yellow-billed Cuckoo (Coccyzus americanus) are divided into three molt series and those of the Common Cuckoo (Cuculus canorus) into four series and, further, that Yellow-billed Cuckoos replace their rectrices in two molt series. Multiple molt series make it impossible to consistently describe primary replacement as a unique sequence of feather loss, as earlier researchers have attempted to do for cuckoos. We calculated the mean number of days (± SE) required to replace the primaries in each molt series. Primary replacement takes considerably less time in the larger Common Cuckoo than in the smaller Yellow-billed Cuckoo, mostly because Common Cuckoos replace four primaries at a time whereas Yellow-billed Cuckoos replace only three at a time. The primaries of Common Cuckoos cannot be better allocated into four molt series such that the time required for their replacement would be reduced, but molt duration would be reduced in Yellow-billed Cuckoos if their primaries were differently allocated into three replacement series. Both species replace their primaries faster than birds of similar size whose primaries are organized in a single replacement series.

North American wood-warbler species (Parulidae) studied to date have song systems of one or two categories. Those with two categories use them in different temporal and behavioral contexts, which suggests similar functions across species. We conducted the first detailed analysis of the vocal behavior of a species in the genus Cardellina, the Canada Warbler (C. canadensis). We found that males had two performance-encoded song categories, Mode I and Mode II, and used them in contexts similar to those in which parulids of the genera Vermivora, Mniotilta, and Setophaga use their song categories. Males sang Mode I more often during the day, when unpaired, during early nesting, and when alone or near a female. Males sang Mode II at dawn, after pairing, during the postfledging period, and when near another male. In Mode I, males sang more stereotyped songs more slowly and regularly. In Mode II, males sang more variable songs rapidly, with a more variable rhythm, and chipped frequently between songs. Although each male included phrases in Mode II songs that he did not use in Mode I, the same phrases were used by other males in Mode I, which indicates that song categories were not form-encoded. Unlike Setophaga species with performance-encoded categories, individual males used most (80%) of their phrases in both categories. The song system of the Canada Warbler, two performance-encoded categories without separation of individuals' repertoires into two distinct parts, is unique among parulids studied thus far, and may provide insight into the evolution of parulid repertoire specialization.

Detailed descriptions of song structure are critical to understanding the ontogeny, evolution, and function of bird song, particularly for species with large song repertoires. We provide a first detailed characterization of song organization and variability in a migratory population of House Wrens (Troglodytes aedon) breeding in western Canada, using a sample of 15,608 songs from 15 males. Males sang with high intensity in protracted bouts prior to pairing and often resumed high-intensity singing later in the breeding cycle to attract a second mate. The high-amplitude terminal portion of songs comprised rapid trills of frequency-modulated notes organized into discrete syllable types with a mean of 10 syllables and 4 syllable types per song. The population syllable repertoire was large (n = 27) and mostly shared but was used to produce much larger repertoires of song types, most of which were unique. Individual males sang up to 194 different song types, with no evidence of a ceiling. However, males sang most song types only rarely and, thus, had much smaller “effective” repertoires of ∼25 song types. Within singing bouts, males also repeated song types many times before switching and modified the syllable contents of successive songs gradually. Hence, they combined tremendous global song diversity with limited real-time song variability. This mix may reflect central neural or peripheral motor constraints on short-term song diversity or, perhaps, selection simultaneously favoring both diversity and consistency in song performance.

Attendants of Neotropical mixed-species flocks are hypothesized to benefit primarily by gaining protection from predators, while potential costs have received little attention. The Wedge-billed Woodcreeper (Glyphorynchus spirurus) frequently joins mixed-species understory flocks but also often forages alone. We hypothesized that, because of the significant vertical component of its foraging behavior, the primary cost to flock-following might be a decrease in foraging efficiency associated with conforming to flock movement patterns. We compared the foraging behavior and microhabitat use of Wedge-billed Woodcreepers in and out of flocks at Tiputini Biodiversity Station, eastern Ecuador, during January–March, 2010–2012. We measured foraging height range, time spent per trunk, vertical movement rate, distance flown between trunks, extent of foliage cover around the focal bird, hitch rate, and peck rate. We tracked birds in 2012 using radiotelemetry to measure horizontal movement rates and to record the locations of flock-joining and -leaving. Wedge-billed Woodcreepers in flocks foraged in more exposed microhabitats, moved vertically at a faster rate despite a decrease in foraging height range, and exhibited greater hitch rates than individuals foraging alone. Peck rates, peck:hitch ratio, and distance flown between trunks did not differ between situations. Horizontal movement rate did not differ in and out of flocks, but the length of flock-following sessions was negatively correlated with movement rate above a threshold of 4 m min^-1. These observations are consistent with an antipredator benefit of flocking for this species and suggest an energetic or foraging efficiency cost associated with conforming to flock movement patterns.

Patterns of nest defense against predators by ground-nesting bird species in the wild are poorly understood, largely because of a historical inability to directly monitor nests. Most nest-defense studies have observed responses elicited from artificial predators or human observers presented to nesting birds, and few have attempted to present these events in the context of predator—prey relationships found in the wild. We hypothesized that predator threat level (e.g., the threat posed to the clutch or to the clutch and the attending adult), parental characteristics, clutch investment, and future reproductive opportunities would influence avian nest-defense decisions. During 1999–2006, we examined predation events (n = 242) from 790 video-monitored Northern Bobwhite (Colinus virginianus) nests. We evaluated parental, predator, daily, and seasonal correlates that potentially contributed to patterns of nest defense by Northern Bobwhites using a model selection approach. The top model showed that nest defense was strongest at nests with larger predators that posed a threat to both adults and the clutch. This model also contained clutch size, but parameter estimates suggest that predator type was the only significant factor determining rates of nest defense. Our results suggest that Northern Bobwhites use the threat posed to the nest and the attending adult by the approaching predator as the primary cue in decisions to engage in nest defense.

Within the Neotropical genus Sporophila, a group of eight species known colloquially as “southern capuchinos” shows remarkable phenotypic variation despite lack of (species level) mitochondrial DNA monophyly and extremely low differentiation in other putatively neutral genetic markers. Previous studies have interpreted this as reflecting recent common ancestry and, perhaps, ongoing hybridization and introgression. A recent taxonomic revision of the only polytypic southern capuchino species, Sporophila bouvreuil (with four previously recognized subspecies), prompted the designation of S. bouvreuil and S. pileata as two distinct species on the basis of plumage color and geographic distribution. We used DNA sequence and microsatellite data to corroborate these new species designations and explored for the first time the relationship between these taxa and the remaining southern capuchinos. Phylogenetic and population genetic analyses showed that S. bouvreuil and not S. minuta, as was previously thought, is the sister species to the core radiation of which S. pileata is part. Our data suggest that the ancestor of the southern capuchinos is derived from northern South America and began to radiate during the lower to middle Pleistocene into at least eight species within the grasslands of northeastern Argentina, eastern Paraguay, and southern Brazil. Consistent with earlier studies, we could not distinguish among southern capuchino species using neutral genetic markers, an expected signature of a rapid and recent radiation.

With limited resources for habitat conservation, the accurate identification of high-value avian habitat is crucial. Habitat structure affects avian biodiversity but is difficult to quantify over broad extents. Our goal was to identify which measures of vertical and horizontal habitat structure are most strongly related to patterns of avian biodiversity across the conterminous United States and to determine whether new measures of vertical structure are complementary to existing, primarily horizontal, measures. For 2,546 North American Breeding Bird Survey routes across the conterminous United States, we calculated canopy height and biomass from the National Biomass and Carbon Dataset (NBCD) as measures of vertical habitat structure and used land-cover composition and configuration metrics from the 2001 National Land Cover Database (NLCD) as measures of horizontal habitat structure. Avian species richness was calculated for each route for all birds and three habitat guilds. Avian species richness was significantly related to measures derived from both the NBCD and NLCD. The combination of horizontal and vertical habitat structure measures was most powerful, yielding high R² values for nationwide models of forest (0.70) and grassland (0.48) bird species richness. New measures of vertical structure proved complementary to measures of horizontal structure. These data allow the efficient quantification of habitat structure over broad scales, thus informing better land management and bird conservation.

Relating population density to spatially explicit habitat characteristics can inform management by directing efforts to areas with lower densities or focusing conservation and land protection on high-density areas. We conducted point-transect surveys for the endangered Golden-cheeked Warbler (Setophaga chrysoparia) and Black-capped Vireo (Vireo atricapilla) in the live-fire region of Fort Hood, Texas. We used mark—recapture distance sampling and combined a Horvitz-Thompson estimator with a habitat-based, resourceselection gradient to estimate spatially explicit density for both species. We detected Golden-cheeked Warblers at 120 locations (202, 197, and 89 detected by primary, secondary, and both observers, respectively) and Black-capped Vireos at 173 locations (241, 255, and 107 detected by primary, secondary, and both observers, respectively). For Golden-cheeked Warblers, the average (± SE) composite detection probability estimate within a 100-m point-sample radius was 0.57 ± 0.14, and for vireos it was 0.24 ± 0.02. Estimated mean density (singing males ha^-1) was 0.14 ± 0.03 (95% confidence interval [CI]: 0.08–0.23) and 0.47 ± 0.05 (95% CI: 0.38–0.60) for Golden-cheeked Warblers and Black-capped Vireos, respectively. Our analysis suggested evidence of heterogeneity in the detection process for both species, as well as imperfect detection at distance g(0), both of which would bias estimated densities if ignored. Additionally, both species exhibited spatial variability in estimated densities, with those areas that had higher occurrence probabilities typically having higher estimated density. In the absence of spatially explicit density prediction, managers must treat all losses of potential habitat for endangered species uniformly, despite likely differences in conservation value. Our approach could be used to ascertain areas of changing density in relation to changing habitat conditions over time and space.

Abundance estimators that account for imperfect detection, such as N-mixture models, assume that detection of individuals is independent of abundance. Using spot-mapping and N-mixture models applied to point-count data, we estimated abundance of Goldencheeked Warblers (Setophaga chrysoparia) in two years at six study sites at the Balcones Canyonlands Preserve, Austin, Texas. N-mixture model estimates deviated from spot-mapping estimates at the site level by overestimating at low abundances, and at the survey-station level by underestimating at high abundance, which suggests that model assumptions may have been violated. We tested whether detection of individuals is influenced by abundance by assessing per capita song rate in relation to abundance. Per capita song rate increased with abundance, illustrating how the behavior of a territorial passerine may violate the independent-detectability assumption. We next explored violation of this assumption at the survey-station level by applying N-mixture models to simulated data exhibiting heterogeneity in detection. This exercise revealed a slight but increasingly negative bias (underestimation of abundance) in the estimator as the actual abundance increased, given positive density-dependent detection. The simulations also revealed a potentiel effect of sampling variation on misestimation by N-mixture model estimators. Assessing the strength, basis, and prevalence of density-dependent detection; further analyzing the effects of nonrandom heterogeneity in producing estimator bias; and accounting for nonrandom detection heterogeneity in abundance estimators are fruitful areas for further study.

Molecular markers and stable isotopes have provided important insights into the migratory connectivity of small landbirds. Research integrating these two methods has primarily focused on linking breeding and wintering sites, rather than focusing on timing of migratory movement of different breeding populations. We used mitochondrial DNA and isotopic markers to infer the timing of various breeding populations of migrating Wilson's Warblers (Cardellina pusilla) moving through a migratory stopover site, demonstrating the value of multiple sources of information in estimating the origin of migrants. Using mixed-stock analysis, we found that early spring migrants sampled in southwestern Arizona were dominated by warblers migrating to the West Coast of the contiguous United States, whereas later migrants included a large pulse of birds migrating to Alaska and western Canadian provinces. Stable hydrogen isotope data from individual birds showed the same timing pattern as genetic data. Had we used stable isotopes alone, we would not have been able to infer whether birds later in the migration season were most likely migrating to Alaska or the Interior West, given the large overlap in isotope values between those regions. The lack of mitochondrial group 2, common in the Interior West, in late-season migrants strongly suggests that these birds were migrating to breeding areas in Alaska or other northern regions. Studies that reveal the timing of migration of different breeding populations through stopover sites lay the foundation for more in-depth examination of seasonal interactions between migration and the stationary phases of the annual cycle.

Regular replacement of flight feathers is one of the most time-consuming activities in the annual cycle of flying birds. In principle, birds can decrease the time required to renew feathers by increasing the rate at which individual feathers grow and by growing more feathers simultaneously. Using 52 comparisons of 43 species from 26 families of birds that maintain the ability to fly while molting, we show that the average number of primary feathers growing simultaneously explains 60.0% of the variation in mass-corrected molt duration, whereas feather growth rate explains only 4.4% of the variation in mass-corrected molt duration. The trend is even stronger when species that grow all their primaries simultaneously are included in the analysis. We suggest that the rate at which feather tissue is produced cannot increase without compromising feather quality because the size of the feather follicle constrains the speed at which feathers can be generated. Thus, birds that must molt rapidly to meet time constraints in their life cycle may be forced to reduce the time spent molting mostly by growing more feathers simultaneously.

Current evidence suggests that the health effect of avian feather mites is minimal. However, feather mites can still proliferate without effective preening, such as might occur during sickness. House Finches (Haemorhous mexicanus) are prone to infection by Mycoplasma gallisepticum, symptoms of which include conjunctivitis. Impaired vision and lethargy associated with the disease may limit preening ability. We examined trapping data from a 4-year study of Mycoplasma infection dynamics in House Finches in Atlanta, Georgia, to determine whether birds with conjunctivitis had higher feather mite loads. Abundance of feather mites (Proctophyllodes spp.) and conjunctivitis severity were visually scored on >800 House Finches of known age and sex. Feather mite abundance showed a distinct seasonal pattern: mite loads increased in July and remained high through January. Limiting the analyses to these months, we found that average mite scores were higher in birds with (n = 94) than in those without (n = 275) conjunctivitis, and mite loads increased with conjunctivitis severity. Although not significant, the mite scores in recaptured birds in relation to infection status support the other findings in the present study. Although these results from field-collected birds do not demonstrate cause and effect, they are consistent with prior studies in which feather mites increased in experimentally infected birds. The implications of this proliferation for the birds require further study, but given that feather mites consume oil and debris from feathers, their high numbers during illness could be beneficial.

The period of growth prior to fledging is a critical life stage for most birds, and shifts in diet during ontogeny may affect growth and development. We used nitrogen (δ¹⁵N) stable isotopes in feather tissue to quantify dietary composition and evaluate the relationship between diet and growth in prefledging Greater Sage-Grouse (Centrocercus urophasianus). Sequential sampling of δ¹⁵N from feather tissue that was synthesized throughout growth allowed us to evaluate changes in plant versus invertebrate contributions to chick diet during the first 28 days posthatch. Feathers became depleted in δ¹⁵N throughout growth, and Bayesian mixing models suggested that the proportional contribution of invertebrate nitrogen declined with chick age. We estimate that invertebrate contributions to the protein in chick diets decreased from 39% at 1 week to 23% at 4 weeks of age, which is consistent with previous research on sage-grouse that used traditional diet-sampling methods. Chicks with feather δ¹⁵N values that spanned a larger range, but had an intermediate mean, had the longest tarsi and greatest mass at 28 days. These chicks also displayed a more rapid transition to herbivory during the prefledgling period. These patterns are consistent with greater importance of invertebrates during early growth but also suggest that a rapid transition to a more herbivorous diet ultimately results in the highest growth rates. Sequential sampling of feather δ¹⁵N provided useful information on temporal patterns in chick diet that were directly relatable to growth during the prefledging stage, and we encourage replication of our approach in other systems.

Life history theory predicts a tradeoff between reproductive effort and survival, which suggests that some management practices aimed at increasing productivity may compromise population growth. We analyzed a 10-year data set of 225 individually marked Snowy Plovers (Charadrius nivosus), a threatened shorebird, to determine whether individual reproductive effort was correlated with low apparent survival. Most adults resided in the population an average of 2 years (range: 1–10 years), during which females laid 3–60 eggs, and both males and females invested considerable time in incubation and brooding. Apparent survival varied annually and was higher for males than for females. Contrary to theory, we found no evidence that increased reproductive effort, either current or cumulative, compromised survival. Instead, apparent survival was correlated positively with incubation time, which may be related to either high-quality individuals having high reproductive rates and high survival or permanent emigration of failed breeders (who incubated for shorter intervals). Although our results suggest that some predator management practices (e.g., nest exclosures) aimed at increasing productivity will not compromise survival in a subsequent year, we caution that these same practices may have serious negative consequences for population growth if (1) reproductive effort does not translate into higher per capita fledging success and (2) direct mortality of adults results from the practice.

The occurrence of extrapair paternity (EPP) in socially monogamous species varies greatly among species and across latitudes. Recent work suggests that birds residing in less seasonal, tropical environments will have lower levels of EPP than seasonal tropical and temperate species. Less seasonal tropical birds are predicted to have the lowest rates of EPP because their presumed low breeding densities and low breeding synchrony may reduce the opportunities for extrapair mating, and their potentially higher adult survival and longer-term pair bonds may increase the costs of retaliation by males, resulting in reduced paternal care. Nevertheless, the limited number of studies in tropical regions impedes our understanding of whether EPP varies across environments and why. We report on rates of EPP and the potential underlying mechanisms for the observed rate in the Black-crowned Antshrike (Thamnophilus atrinucha, previously known as the Western Slaty Antshrike), a Neotropical and socially monogamous passerine residing in a relatively aseasonal environment. The birds had low rates of EPP, with 3% of offspring (3 of 89) in 4% of broods (2 of 50) being sired by extrapair males. Results are inconsistent with expectations that breeding density and variation in breeding synchrony influence EPP within the population, given the observed high density and high variation in breeding synchrony without simultaneous changes in EPP. The costs of retaliation by males, which provide extensive parental care, and the benefit of long-term pair bonds may lead to few females engaging in extrapair matings despite opportunities for doing so. Our results are consistent with predictions that aseasonal tropical species have lower EPP than seasonal tropical and temperate species.

Knowledge of breeding dispersal, defined as shifts in territory location between two successive breeding seasons, remains limited for migratory passerines. We investigated the relationship between two ecological factors, habitat structure and reproductive success, and 499 breeding dispersal events in a Nearctic—Neotropic migratory songbird, the Black-throated Blue Warbler (Setophaga caerulescens) breeding at the Hubbard Brook Experimental Forest, New Hampshire, from 1998 to 2008. Male dispersal distance was correlated with both individual age and habitat structure, with older males moving shorter distances than younger males, and males on the high-shrub-density plot (i.e., higher quality) moving shorter distances than males on the plot with lower shrub density. Female dispersal distance was also correlated with habitat structure; individuals on the higher-quality plot moved shorter distances than those on the lower-quality plot. In contrast to that of males, female dispersal distance was independent of age, but correlated with reproductive success: females that fledged relatively few offspring in a year subsequently dispersed farther than those that experienced high reproductive success. Mean (± SE) breeding dispersal distance for females (245 ± 20 m) was greater than that of males (163 ± 11 m). We also examined reproductive consequences of breeding dispersal and found that males that moved shorter distances fledged more offspring after dispersal than those that moved longer distances; no trend was found for females. These differences in dispersal patterns and outcomes suggest sexspecific selective pressures and life-history strategies.

Nest-habitat selection in colonial species has rarely been assessed at multiple spatial scales to evaluate its fitness consequences. Management for the federally endangered U.S. Interior population of Least Terns (Sternula antillarum) has focused on maintenance of breeding habitats, including mechanical construction of sandbars from dredged material. Least Terns are attracted to large areas of unvegetated substrate, yet small-scale habitat features are thought to trigger selection for nesting. We evaluated nest-scale habitat selection to determine (1) whether selection differs between constructed and natural sandbars and (2) the subsequent consequences of habitat selection on nest success. During 2006–2008, we examined 869 Least Tern nest sites on constructed and natural sandbars in the Missouri River for evidence of microhabitat selection at the nest in relation to habitat within the surrounding 3-m area. Least Tern nest sites had coarser and larger substrate materials at the nest, more debris, and less vegetation than the surrounding area. Nests in constructed habitats had a greater percentage of coarse substrates and less vegetation or debris than nests in naturally created habitats. Apparent nest success was 1.8× greater on constructed than on natural sandbars. Nest success was best predicted by models with two spatial scales of predictors, including substrates (nest) and vegetation and debris (nest or surrounding area). Our results indicate that Least Terns select nest microhabitat characteristics that are associated with wind- and water-scoured habitats, and that nest success increases when these habitats are selected.

The influence of vegetation structure on the probability of daily nest survival (DNS) for grassland passerines has received considerable attention. Some correlative studies suggest that the presence of woody vegetation lowers DNS. Over 3 years (2009–2011), we monitored 215 nests of the Grasshopper Sparrow (Ammodramus savannarum) and Henslow's Sparrow (A. henslowii) on 162 ha of reclaimed surface-mine grasslands in Pennsylvania. We removed shrubs from treatment plots with ≤36% areal coverage of woody vegetation in a before-after-control-impact-pairs (BACIP) design framework. Daily nest survival (95% CI: 0.94–0.96) was as high as previous studies have reported but was not associated with woody vegetative cover, proximity to woody vegetation, or woody stem density. Variation in DNS was best explained by increasing nonwoody-vegetation height. Grasshopper Sparrow fledgling production on treatment plots in 2010 (95% CI: 3.3–4.7) and 2011 (95% CI: 3.8–5.0) was similar to baseline conditions of treatmentplots (95% CI: 3.4–4.9) and control plots (95% CI: 3.2–4.5) in 2009. Fledgling production was associated with thatch depth (β ± SE = 0.13 ± 0.09) and bare ground (β ± SE = -2.62 ± 1.29) adjacent to the nest and plot woody vegetative cover ( ± SE = -3.09 ± 1.02). Our experimental research suggests that overall reproductive success of Grasshopper and Henslow's sparrows on reclaimed surfacemine grasslands is driven by a suite of largely nonwoody—vegetation components, and both species can successfully nest and produce young in habitats with greater amounts of scattered woody vegetation than has generally been considered.

Many waterbirds reproduce seasonally in response to fluctuations in food supply. White-shouldered Ibises (Pseudibis davisoni) breed during the dry, water-drawdown season, but, unlike other waterbirds, they do not take advantage of prey concentrated in diminishing pools. To understand how this species successfully feeds and breeds at the driest time of year, we studied its habitat use and diet, and the habitat conditions that influence intake rates and prey density at waterholes. Foraging observations, prey sampling, and landscape-scale assessment of habitat availability were undertaken (at 7, 47, and 58 waterholes, respectively) over two breeding seasons. Although they rarely foraged in water, the birds used all exposed substrates, feeding on amphibians and small invertebrates. Amphibians were the most abundant prey in waterhole substrates and accounted for 81% of overall biomass intake. Both intake rates and density of amphibian prey biomass were greater in dry than in moist or saturated substrates. Intake rates and density of prey biomass changed little through the dry season, but exposed substrate extent increased by 74%. The White-shouldered Ibis's use of dry waterhole substrates to exploit seasonally concentrated prey is unusual among large waterbirds, and we suggest that its breeding season may be timed to coincide with receding water levels and increasing substrate exposure. Estimated prey requirements of a breeding pair over the nesting period were equivalent to nearly two-thirds of amphibian biomass found at large waterholes. Each pair may therefore require multiple waterholes to overcome prey depletion and breed successfully, which is consistent with the noncolonial dispersed distribution of nesting pairs.

Understanding how weather influences survival and reproduction is an important component of forecasting how climate change will influence wildlife population viability. Nest predation is the primary source of reproductive failure for passerine birds and can change in response to temperature. However, it is unclear which predator species are responsible for such patterns because predation events are rarely observed. We investigated whether temperature influenced predator-specific rates of nest predation by analyzing data from six prior studies conducted between 1997 and 2010 in Texas, Illinois, and Missouri that used constant-surveillance video systems to identify predators at the nests of Golden-cheeked Warblers (Setophaga chrysoparia), Blackcapped Vireos (Vireo atricapilla), Indigo Buntings (Passerina cyanea), and Acadian Flycatchers (Empidonax virescens). Rates of nest predation by snakes and birds increased as daily maximum temperatures increased, whereas predation by mammals was essentially invariant in response to temperature. The relative roles of physiological versus community-level mechanisms (e.g., abundance or behavior of predators and/or alternative prey) in driving the patterns we observed remain unclear, but our data point to the need to consider important biological interactions when forecasting the effects of climate change on songbird populations.

An analysis of morphology, vocalization, habitat preference, and distribution revealed that the southern yellowbilled population ascribed to the Plumbeous Seedeater (Sporophila plumbea) is actually an undescribed species. Individuals of this new species are distinguishable from other Sporophila, particularly S. plumbea, by a combination of diagnostic characters: (1) the adult male has a robust, bright yellow bill with an arched culmen, distinguishing it from S. plumbea and other gray seedeaters; (2) the adult male is larger and heavier than S. plumbea; (3) the adult plumage of males is bluish gray (not plumbeous gray, as in S. plumbea); (4) vocalizations include song that is structurally similar to that of S. plumbea but with clear (whistled) introductory syllables and unique call notes. The new seedeater is segregated from other gray seedeaters in its breeding habitat and breeding distribution. It is endemic to Brazil, where it breeds in upland shrub-grasslands associated with Araucaria forests in southern Brazil and migrates northward to the Cerrado to winter.