Studies of geographic variation of bird vocalizations facilitate the understanding of species' divergence and evolutionary histories, as vocal traits vary in response to different factors including the environment, morphology, culture, and inheritance. The Acorn Woodpecker (Melanerpes formicivorus) is a non-passerine species of the family Picidae, and therefore its vocalizations are not acquired through learning. It is widely distributed throughout the Americas and exhibits distinctive morphological and genetic differences among the 7 allopatric subspecies, but little is known about geographic variation in the structure of its vocalizations and whether vocal variation corresponds with their genetic differences. We collected recordings throughout the species' range and assessed the frequency and temporal features of their most common calls to study geographic variation in vocalizations. Specifically, we tested whether divergence in vocal traits mirrored subspecies limits. Our results showed the formation of 2 vocal groups that do not reflect subspecies limits. The genetic divergence described in previous studies coincides with the vocal divergence found in this study, with 2 areas promoting the greatest divergence: the Isthmus of Tehuantepec and the Gulf of California. Previously described morphological variation in bill sizes also coincides with the vocal groups found in this study, in which large and small sizes are grouped separately.

After the breeding season, territorial adult Black-crested Titmouse (Baeolophus atricristatus) and residing juveniles form social groups that may persist until the following spring. Under the prolonged brood care hypothesis, one would expect these juveniles to be retained offspring with delayed dispersal of the breeding pair. To test if Black-crested Titmouse juveniles that reside in post-breeding territories are offspring of the territorial adult male, we performed microsatellite-based paternity analyses of 6 juvenile–adult male social dyads on 6 different territories. None of the juveniles were offspring of the adult male with which it shared a territory. We discuss several possible evolutionary explanations for this result.

North American birds have declined by 29% over 48 years, with declines occurring across species and biomes. To examine population patterns at a local scale, we investigated species and population shifts in a forest bird community in northeastern Connecticut. We did so in relation to its changing environments, focusing on patterns consistent with the effects of climate change and habitat manipulation. In 1985, we established survey routes primarily in the intensively managed Yale-Myers experimental forest, which we repeated in 2018 and 2019. Species richness varied little from the initial survey to the recent ones, although population density increased by 24% after 1985. Turnover in species composition exceeded 50%. The 5 most strongly declining species were northerly distributed, forest interior inhabitants, whereas the 7 most strongly increasing species were variously distributed forest interior and edge/successional-associated species. Some species experienced increases by invading new habitats, whereas at least one appeared to decline due to interspecific competition. Expected effects of climate change on populations were consistent with some findings, but habitat effects appeared related to a greater number of shifts. However, much contrary data indicated that these factors were not alone in driving community change. This bird community may best be thought of as a dynamic assemblage that represents the sum of individualistic responses to environmental and perhaps stochastic factors.

An important goal of urban ecology is determining what differentiates urban-tolerant populations of birds from their non-urban ancestors and urban-intolerant species. One key to urban success may be reacting appropriately to human activity, and the degree to which birds view humans as threats can be quantified by their escape behavior. Understanding individual-level plasticity, however, requires the tracking of known individuals. We compared flight-initiation distances (FID) and distances fled (DF) from approaches by a human between an urban and a non-urban population of individually marked Dark-eyed Juncos (Junco hyemalis) in Southern California. The urban population is more tolerant to people as evidenced by attenuated FIDs and DFs relative to non-urban birds. Although individual urban birds either habituated or sensitized to repeated approaches, there was no significant pattern at the population level. Overall, the behavioral patterns exhibited by this urban population of juncos is more supportive of in situ evolution of tolerance than either being a biased sample from an ancestral non-urban population or intrinsic behavioral plasticity that produces a uniform adjustment to urban life.

I examined images of over 6,300 individual hummingbirds from the Cornell Lab of Ornithology's Macaulay Library to clarify conflicting reports on molt and plumage strategies in 8 species that breed or have bred primarily in the southwestern United States. Fixed replacement sequences from 2 nodes among primaries and 2 nodes among secondaries were found without exception, conforming to the findings of previous studies. I concluded that the preformative molt varied from limited to partial in 3 species, partial to incomplete in 3 species, partial to complete in 1 species, and complete in 1 species. Results of this study clarify molt terminology in Trochilidae as based on evolutionary homologies, and they establish new criteria for age determinations. The Macaulay Library clearly provides an important resource for the investigation of avian molts and plumages. I present a road map for such studies and suggest many other questions on avian molt that can also be investigated. I encourage contributors to the Macaulay Library to take and upload images of birds in molt or in worn plumages.

The High Andean peatlands are peat-accumulating wetlands dominated by cushion-forming plants and are embedded in a matrix of puna grasslands above 4,000 m. These ecosystems are an essential source of water and evergreen vegetation for wild and domestic animals and are considered sensitive to environmental alterations. We studied the birds' habitat and microhabitat preference in peatlands and their surrounding grasslands in the Cordillera Real, Bolivia. We established 3 parallel transects around 12 peatlands: (1) in peatland, (2) at 100–200 m from the peatland edge, considered as the transition habitat between peatlands and grasslands, and (3) in puna grasslands at >500 m from the peatland edge. We quantified bird abundance, species richness, and the availability of 8 microhabitats along 36 transects. We recorded 934 individuals of 34 species and found higher bird species richness and abundance in peatlands than in surrounding grasslands and transition habitats. We found that 26% of bird species were exclusive to peatlands. While most bird species common in peatlands were almost nonexistent in other habitats, most species associated with grasslands were also found in proximity to peatlands. A canonical correspondence analysis showed that bird species were associated with one or more microhabitats. The high abundance, bird species richness, and diet types in peatlands is probably related to the high primary productivity of peatlands and year-round availability of water. Degradation of these peatlands may reduce the abundance of regional bird communities, not only peatland specialists but also species in surrounding habitats.

This study presents the first description of the breeding biology of the IUCN Endangered North Philippine Hawk-Eagle (Nisaetus philippensis). We describe a single pair's breeding phenology, nest characteristics, diet, chick development, and behavior through on-the-ground and remote observations from 1 February to 14 May 2020. Due to limited mobility during the COVID-19 pandemic, we improvised a video recording setup for remote monitoring and used machine learning to extract data from images. The nest was a low cup/fork type stick nest placed on a Malabulak tree (Bombax ceiba) in a heavily disturbed secondary forest. When it was first found, the incubation stage was underway and lasted for 1 month as the nestling emerged on 1 March 2020. Both adults provided parental care throughout the breeding period, with the male primarily providing food and the female attending to the nest, egg, and chick. They preyed on a wide range of vertebrates such as lizards, ground birds, bats, rodents, and domestic animals. With a single egg per clutch and a relatively long breeding cycle, the species has a slow reproductive output that may contribute to its current threatened status.

Birdsong is commonly associated with sexual selection. It can influence mate choice through honestly signaling the emitter's quality. Such quality may be reflected, among other factors, in body condition and bite force. The Green-winged Saltator (Saltator similis) is a good model species to assess such relationships because males defend their territories throughout the year and sing a stereotyped song, which is known to be associated with sexual selection. The objective of this work is to assess the relationships among song structure, vocal individuality, and possible fitness indicators (body condition, morphology, and bite force) in captive male Green-winged Saltators. We conducted a linear discriminant analysis (LDA) to assess vocal individuality and to highlight the principal acoustic variables associated with it. We conducted Y-Aware PCAs to evaluate the relationship between the body condition index, bite force, and morphometric and bioacoustic variables. The morphometric variables, particularly head width and length, explained 23% of the bite force variation. The acoustic variation explained 36.17% of body condition index variation, but a small nonsignificant amount of bite force (12%). From the acoustic variables, peak frequency and high frequency of the last syllable, slope of the first syllable, and emission rate showed significant negative relationships with body condition. The LDA model based on acoustic variables had a 97.47% accuracy, although this result might also reflect regional song dialects. The acoustic variables most relevant to individual classification (first syllable duration, last syllable duration, whole-song slope, and whole-song duration) are not the same variables that had a stronger relationship to body condition. Besides that, there can be a weaker mixed signaling, as variables related to frequency modulations were important in both contexts. Our results suggest that the song may act as an honest signal of an individual's body condition in this species.

The Whooping Crane (Grus americana) is an endangered species that historically comprised both migratory and nonmigratory populations in North America. Currently, there is one wild migratory and multiple reintroduced (both migratory and nonmigratory) populations of Whooping Cranes. Individual cranes in reintroduced populations are marked with unique color bands and transmitters, allowing for intensive monitoring throughout their lives. In spring 2011, a 6-year-old migratory female Whooping Crane separated from her migratory mate at a wintering site in Alachua County, Florida. She then began associating with a nonmigratory male Whooping Crane originally released in the same area. The 8-year-old nonmigratory male then proceeded to migrate to Wisconsin with the female in April 2011; however, upon returning to her nesting territory, the female returned to her previous mate. The Florida male remained in Wisconsin for ∼12 d before returning to Florida by 5 May, traveling at least 4,451 km in 1 month. The reason for this long-distance move may be that the Florida male crane had recently lost his mate and was hoping to pair with the migratory female. This is the first record of a Whooping Crane completing a roundtrip long-distance movement in 1 season, which raises questions about drivers of migration in cranes.

The Hawaiian Stilt (Himantopus mexicanus knudseni) and Hawaiian Gallinule (Gallinula galeata sandvicensis) are federally endangered waterbirds endemic to the Hawaiian Islands. Both species are conservation-reliant; their population persistence is dependent on invasive predator control and removal of invasive plants that degrade habitat. We present observations of successful nesting by one Hawaiian Stilt pair and one Hawaiian Gallinule pair at a site managed within an adaptive Indigenous agroecological framework on the island of O‘ahu, Hawai‘i. The Hawaiian Stilt nest, found in February 2019, contained 4 eggs and produced 3 hatchlings, 2 of which were banded and monitored after hatching. The Hawaiian Gallinule nest, found in February 2020, contained 6 eggs and produced 5 hatchlings. Although no individuals were banded from this nest, 2 adults and 2 hatchlings were continuously observed in the nesting area after the eggs hatched. Lo‘i kalo Hawaiian wetland agroecosystems centered around the cultivation of kalo (taro; Colocasia esculenta), have the potential to expand Hawaiian waterbird habitat beyond state and federal protected areas. We are aware of unpublished accounts of Hawaiian waterbirds nesting in commercially farmed lo‘i kalo, but until now, there have been no previously published accounts of native waterbirds breeding in lo‘i kalo managed as Indigenous agroecosystems.

Natural history information is one of the major knowledge gaps in Neotropical ornithology. Several range-restricted and threatened species in the region are still poorly known, hindering the design of effective conservation programs. Here, we used direct observations collected at 7 localities throughout the Tropical Andes to describe habitat use and foraging ecology of the Yellow-headed Brushfinch (Atlapetes flaviceps), a species of conservation concern and endemic to Colombia. Our observational records (n = 174) indicate that this species mainly occurs in secondary forests and landscape mosaics that include patches of native vegetation and agricultural areas, but it seems to be frequently associated with the presence of regenerating vegetation in early successional stages. We found that the species' diet was mainly composed of fruits and invertebrates, although other items are occasionally included. Although our data suggest the possibility of an association between habitat type and the activity recorded, as well as temporal variation in foraging behavior, this requires more research. Our observations support the idea of this species being tolerant to human-altered habitats, but this needs to be confirmed by measuring habitat-specific productivity and survival. The results presented here not only increase knowledge of this poorly known endemic but can be useful for the subsequent implementation of management strategies aimed at increasing the availability of high-quality habitat.

The Gray-headed Tanager (Eucometis penicillata) has 7 subspecies widely distributed in Central and South America. Scattered reproductive data are available for most of them, but reproductive aspects were thoroughly documented only for E. p. stictothorax, from Costa Rica. Here, we provide detailed descriptions of nests, eggs, and nestlings of E. p. albicollis from southeastern Brazil, and compile nesting information available from this and other subspecies from the literature. During the 2019–2020 and 2020–2021 breeding seasons, we found 4 nests that were active from October to January. Nests were deep cups with 8.5–11.1 cm in outer diameter, constructed of loosely attached dry fibers and sticks, and could be supported at their rims, laterally, or from beneath. They were built in riparian forest understory, 1.1–1.5 m above ground, 1.0–10.5 m away from forest streams, and 72–100 m from the forest edge. Clutches consisted of 3 eggs. Eggs were brownish-gray in background color, with dark-brown blotches, measured 21.9 mm (±0.8) in length and 16.2 mm (±0.7) in width, and weighed 3.0 g (±0.3). The hatchlings had reddish skin, bright orange mouth lining, and white commissure. The pair shared nestling provisioning and we also document the first case of brood parasitism by Shiny Cowbird (Molothrus bonariensis) for the Gray-headed Tanager. Upon comparing our data with that of other subspecies, we observed differences in nest material, breeding phenology, clutch size, and eggs and nestling characteristics, which could be attributed to local adaptations of geographically distinct subspecies or to phylogenetic divergences between still unsplit species.

Knemidokoptic mites infest many bird species around the world and may lead to decreased survival, although relatively few studies have documented long-term effects on populations. We present 9 years of data monitoring the survival of Red-winged Blackbirds (Agelaius phoeniceus) in islands of Lake Erie, Ohio, USA. Blackbirds in our study first appeared with mite infestation in 2012. Percentage of the total number of blackbirds infested with mites peaked at 7.3% in 2013 and persisted at 5–6% through the summer of 2018. We saw no differences in infestation rates based on blackbird sex or age. Unlike most other studies, in subsequent years we did recapture birds that had previously had infestations, and we detected no decline in recapture rate due to mite infestation. While that does not mean that blackbirds do not experience negative consequences of infestation, our evidence does suggest that low-level infestation may be persistent in a population without dramatic declines in survivorship.

Efforts to protect the endangered northwest Atlantic population of Roseate Tern (Sterna dougallii) have typically focused on a small number of breeding colonies distributed from Nova Scotia to New York. Yet the species is also potentially vulnerable at staging sites used by adults and recently fledged juveniles preparing for their southward migration to South America. My study found no evidence of pronounced changes in the overall distribution of Roseate Tern fall staging flocks over 5 decades. Coastal Massachusetts, especially Cape Cod, Nantucket, and Martha's Vineyard, annually support large numbers, representing a significant portion of the North Atlantic breeding population, from mid-July through late August. This work provides a long-term review of Roseate Tern fall staging behavior in northeastern North America and a foundation for ongoing and future studies aimed at clarifying specific threats faced by this species at specific staging sites during the post-breeding period.

The Reddish Scops-Owl (Otus rufescens) is a Near Threatened Sunda endemic associated with lowland closed-canopy forests. We radio-tracked the male Reddish Scops-Owl of a breeding pair in the Ayer Hitam Forest Reserve in southwestern Peninsular Malaysia from July to September 2019. From a total of 137 radio fixes, and based on its minimum convex polygon, harmonic mean, and kernel density estimations, the home range of this bird was estimated as 1.31–2.16 ha, with 2 roosts found within this area. Its movement was 39.13 ± 3.27 m h^–1 in the understory forest strata (1–5 m tall) and mostly close to bamboo clumps. We discuss the possible niche partitioning and interspecific interactions of this owl.

Global rising temperatures due to recent climate change have been linked to long-term reductions in body mass and wing chord in migratory birds, including raptors. The Arctic is experiencing higher temperatures compared to the global mean and such high-latitude increases could influence the morphometrics of the tundra-breeding Rough-legged Hawk (Buteo lagopus). Linear regression models showed no statistically significant changes in body mass or wing chords in migratory juvenile male and female Rough-legged Hawks captured and banded across 48 years at Duluth, Minnesota, 1973–2020. Captures of Rough-legged Hawks at our migration stations provided a relatively expedient means by which to monitor possible climate-induced long-term changes in morphometrics of an Arctic species that is difficult to sample in inaccessible tundra settings.

We documented a case of nonparental infanticide at a nest of White-throated Cacholote (Pseudoseisura gutturalis) in 2018 in xeric northwestern Argentina, the first confirmed for the large family Furnariidae. Competition for resources such as food or nest sites, rather than cannibalism or short-term mating opportunities, may underlie this event.

Nest site selection is crucial for survival and fecundity of birds. Predators find nests using visual, aural, thermal, and olfactory cues, yet few studies have evaluated olfactory concealment of nests. Rat snakes (Pantherophis spp.) are common nest predators that use ground-level olfactory cues to detect nest locations. In Arkansas, USA, we evaluated if cavity locations of the Red-cockaded Woodpecker (Dryobates borealis, RCW), a species that experiences nest predation by rat snakes, were associated with airflow conditions known to provide olfactory concealment for other bird species. We used a 3-dimensional sonic anemometer to measure ground-level air velocity, turbulence, and turbulence intensity at cavity trees and unused trees, and at cavity and opposite orientations on trees. For all airflow variables, we found no differences between used and unused trees and orientations. Other factors such as landscape-scale vegetation cover, forest stand structure, and tree characteristics may be more important for providing visual concealment or optimal foraging conditions. However, it remains possible that such factors also convey olfactory concealment. For example, savannah-like forests preferred by RCWs may have greater air turbulence than closed forests. Further research on RCWs and other bird species to address additional aspects of olfactory concealment, and relationships between different dimensions of concealment (e.g., between visual and olfactory concealment), would give insight into how habitat management could provide multiple benefits to birds.

Between 26 and 28 June 2021, the United States' Pacific Northwest endured an unprecedented heatwave that broke previous temperature records by 5 °C. Here, we report the impacts of the heatwave on Bushtit (Psaltriparus minimus) nests being monitored as part of a long-term study in Portland, Oregon. Of the 8 nests active during the event, nestling mortality was 100% in 3 nests and 4 broods survived at least in part. We suspect the excessive heat forced at least one additional brood to fledge early. Remains of nestlings found in 2 nests that eventually fledged suggest that even those encountered brood reduction during the heatwave. Nests with broods that survived were closer to a water source (x̄=13 m) than nests with broods that did not survive (x̄ = 148 m). In addition, surviving broods were younger (either eggs or <4 d of age) than those that perished (>9 d of age). Since these are only the second incidence of total nestling mortality other than depredation observed during Sloane's long-term research on Bushtits in Oregon and Arizona (1986–present), we consider this to be a significant finding and indicative of the future negative effects of global climate change on temperate zone species of breeding passerines.