We developed aging criteria for 7 species of manakins (Pipridae) from the Manu Biosphere Reserve, Peru, based on patterns of plumage maturation and wing-feather replacement following their preformative molt, and summarize information on their morphological characteristics. Each species underwent a partial preformative molt, which could be identified using the presence of molt limits in the greater coverts. Some male Band-tailed Manakin (Pipra fasciicauda), Round-tailed Manakin (Ceratopipra chloromeros), Cerulean-capped Manakin (Lepidothrix coeruleocapilla), and Yungas Manakin (Chiroxiphia boliviana) showed evidence of delayed plumage maturation, allowing for age classification up to the third annual cycle, whereas Blue-crowned Manakin (L. coronata caelestipileata), Fiery-capped Manakin (Machaeropterus pyrocephalus), and Green Manakin (Cryptopipo holochlora viridor) appeared to attain definitive plumage after their second molt cycle. Morphometrics showed strong overlap and were less useful for separation of age and sex classes. Our findings add to the growing list of studies that suggest many tropical passerines can be aged using primarily molt limits. Data on molt and plumage maturation are still needed for the vast majority of tropical birds in order to inform conservation-based research and studies of avian life history.

Urban development reduces the abundance of most natural resources for some birds but also provides new opportunities for others. One group that is more likely affected by urban development is the cavity-nesting species (primary excavators and cavity-adopters), because the main substrates used for nesting, such as dead trees or dirt banks, are frequently removed for security or aesthetic reasons. However, urban development also provides artificial resources that may be used for some cavity-nesting birds such as wooden posts, poles, pipes, holes in house roofs, or building crevices. How cavity-nesting species use these new artificial resources for nesting is poorly understood. Our goal is to provide information on the use of artificial cavities and artificial substrates in urban and human-altered areas for cavity-nesting birds. We opportunistically collected observations of the use of those cavities and substrates from 2003 to 2019 in Costa Rica and found that 20.2% of the 94 Costa Rican bird species that are known to nest in wooden cavities and 9.5% of the 21 Costa Rican bird species that are known to nest in burrows use artificial cavities or artificial substrates for nesting. Although our observations showed that some species are capable of responding to the reduction of natural substrates or cavities in urban habitats through the use of artificial structures, the reproductive success of these birds is still unknown.

Semi-arid vegetation is predominant in Mexico, and the Tehuacán-Cuicatlán Biosphere Reserve is considered one of the most biodiverse semiarid protected areas in the country. The objectives of our study were to evaluate the diversity of ground-dwelling birds through the opportunistic use of camera traps set for monitoring mammal species, and to determine the relationship between bird diversity and 4 environmental variables (distance to rivers, tree cover, shrub cover, and environmental heterogeneity) and 5 anthropogenic variables (distance to roads, human settlements, and agricultural zones, and numbers of cows, donkeys, goats, and people) within the La Cañada region, located inside this reserve. We used bird records from 93 camera-trapping stations taken over the period 2011–2016. In order to evaluate the relationship of bird diversity with environmental variables, a subgroup of 36 camera traps was selected and analyzed using generalized linear models. We recorded a total of 30 bird species in >1,368 photographic records collected over 33,000 camera-trap-days. These birds belonged to 14 orders, 22 families, and represented 23% of the total number of species known to occur in La Cañada. A Clench species accumulation model estimated 38.5 ground-dwelling birds. Record frequency varied significantly among vegetation types and was greater in the crassicaule scrub and tropical deciduous forest (79% of the records). The diversity indices were higher closer to the rivers, and in areas with greater tree coverage and low human activity. High environmental heterogeneity positively influenced the higher diversity of ground-dwelling birds compared to that of sites at greater distance from water bodies or with little vegetation cover. Noninvasive techniques, such as camera-trapping, could be a complementary method for evaluating ground-dwelling bird activity, occupancy, and habitat use. We also recommend that similar opportunistic data of considerable biological and ecological value be published rather than simply archived.

Conversion of natural habitats to urban landscapes is happening at a rapid pace around the globe. Establishing a preserve system and restoring lands within these preserves is one way to offset the loss of natural habitats. However, often when preserves are being developed little data exists outlining the distribution of species and the habitat parameters on which they depend. We used populations of the Cactus Wren (Campylorhynchus brunneicapillus sandiegensis) inhabiting the coastal slope of California to demonstrate how to refine the general gestalt of habitat conditions for the wren into defined parameters that can be used to develop strategic restoration plans. We found that wren habitat use declined to nearly 0% when cactus patches were spaced farther than 800 m apart, regardless of size. The probability of occupancy, or habitat use, rose above 60% when cactus patches were 0.15 ha in size or greater. Elderberry is an important factor in areas with little topographic relief, as it provides perching sites. Buckwheat may not be important to the wren but could be used to select sites that have drier conditions conducive to cacti. Planting cactus to restore ruderal sites properly selected for xeric conditions, and within relatively close proximity to each other, could help meet conservation goals of connecting and increasing wren populations by establishing ecological functions at a landscape level.

Here, we report new distributional information of the Aztec Rail (Rallus tenuirostris), a Mexican endemic that inhabits freshwater marshes throughout the highlands of central Mexico. We found an unidentified rail population during opportunistic area-search surveys between February and May in 2016 and 2017 along the San Pedro and Conchos rivers in Chihuahua, Mexico. Given the high phenotypic similarity between some North American Rallus taxa, we sequenced the mDNA marker ND2 of a specimen and performed a phylogenetic analysis, which allowed unequivocal identification. Maximum likelihood analysis placed the Chihuahuan sample within a clade grouping Aztec Rail samples from central Mexico. We also performed species distribution modeling (SDM) to assess habitat suitability of the newly identified Chihuahuan population of the Aztec Rail, which would account for its possible year-round permanence in the area. SDM results suggest that the Conchos River has the highest habitat suitability, followed by San Francisco del Mezquital. The environmental variables that mostly contributed to SDM were standard deviation of the enhanced vegetation index, annual mean temperature, and precipitation seasonality. The apparently small population of the Aztec Rail in Chihuahua may be either the result of recent dispersals from its core range in central Mexico, or a relict population from a formerly larger distributional range; further studies are needed to clarify this issue.

Flight is one of the most effective yet energetically demanding means of movement. Its energy costs are normally associated with interspecific variation in efficiency, size of organs, and physiological systems that reflect different flight capacities. Adaptive morphological variation may be constrained by physical demands that vary with body size, but work remains to place allometry associated with flight mode in an ecological and evolutionary context. We predicted that heart, lung, and skeletal masses, as well as tracheal diameter, should show a reciprocal positive correlation and have reduced size in species with poor flight capacities. We measured tracheal diameter together with lung, heart, and skeletal mass in 21 species of medium to large body sized game birds. We then compared 7 of these species categorized as short flyers belonging to the order Galliformes with 14 other species capable of sustained flapping flight. Our comparative analyses incorporating phylogeny revealed that once accounting for body mass, Galliformes had smaller heart mass compared to other species, as shown in few previous studies. Additionally, we detected reduced tracheal diameter and lung mass in Galliformes, suggesting the presence of morphological pleiotropy predicted under the concept of symmorphosis. These organs all showed different levels of reciprocal correlations due to their functional connection. Residual skeletal mass was independent of flight capacity and showed no relationship with heart mass, thus indicating that selection for reduced skeletal mass may have already maximized how light a bird skeleton can be, constraining mass-independent variation in this trait. Our results suggest that cardiorespiratory organs have evolved symmorphic variation in size that reflects costs and benefits associated with different flight capacities. However, our observed differences are confounded with phylogenetic history, so additional comparative studies are needed to rigorously test this hypothesis.

While most population genetic studies focus on breeding populations, patterns of genetic structuring of migrating birds can provide similar insights of species distribution, yet population structuring is rarely studied at migratory stopover sites. Philopatric species such as the Eastern Phoebe (Sayornis phoebe) return to the same breeding sites, which reduces gene flow between breeding populations and leads to population structuring. Therefore, we should be able to detect population differentiation at migratory stopover sites if genetically distinct breeding populations converge during migration. Our objective was to determine if we could detect population structuring among migrating Eastern Phoebes of unknown origin. Panola Mountain State Park (PANO) is a restored grassland in central Georgia where phoebes are consistently captured throughout the annual cycle. We collected blood samples from 73 individuals at PANO between November 2017 and January 2019 and amplified 12 highly variable microsatellite loci specific to phoebes. Since the phoebes were of unknown origin captured at the same site, we assigned a priori populations based on (1) season of capture and (2) date of capture. Our F_ST results revealed that phoebes captured during the breeding season are genetically different compared to those captured during fall. These genetic differences are either a result of genetic differences between migratory individuals (fall and wintering seasons) and resident breeding populations (breeding season) or genetically distinct breeding populations that use PANO as a migratory site at different times. While understanding which of these is responsible for our results requires additional study, this study is the first to show population structuring of a migratory species using genetic markers at a migratory stopover site when distinct breeding grounds and populations are otherwise unknown.

We characterize bacteria of the gastrointestinal tract of 28 Northern Saw-whet Owls (Aegolius acadicus) netted on the Mohonk Preserve near New Paltz, New York, during autumn of 2017. We used selective culture media to determine the presence and assess the point infection level of Escherichia coli, Pseudomonas aeruginosa, Salmonella spp., and Staphylococcus aureus in the buccal, cloaca, feces, and pellets of Northern Saw-whet Owls. We tested for associations between bacteria type, sample point location, and infection levels and then assessed the influence of bacterial infection on the health of owls using multivariate analysis of mass/wing chord body condition index estimates and heterophil to lymphocyte ratios. All Northern Saw-whet Owls tested positive for at least one type of bacteria. We found an inverse relationship between the number of bacteria types detected per individual and the percentage of Northern Saw-whet Owls affected, with 46.43%, 32.14%, and 3.57% of individuals showing presence of 2, 3, and 4 types of bacteria, respectively. Multivariate analysis revealed a significantly heightened presence of S. aureus in the buccal cavity, and Spearman's rho analysis revealed positive correlations between site colonization levels and bacterial species levels. We found no significant relationship between bacterial load and mass/wing chord body condition indexes or heterophil to lymphocyte ratios. We did, however, find a positive relationship between heterophil to lymphocyte ratios and Leucocytozoon infections. Providing baseline information of common microflora can help future research recognize potentially harmful gastrointestinal pathogens. Therein, as the first study to characterize bacteria of the Northern Saw-whet Owl, this research adds to the information portfolio of the species and may benefit future research efforts.

We screened 103 Chestnut-collared Longspurs (Calcarius ornatus) and 69 Savannah Sparrows (Passerculus sandwichensis) captured in Alberta, Canada, for infections from 3 genera of hemosporidian parasites (Haemoproteus, Plasmodium, and Leucocytozoon). We used electrophoresis to visualize bands of PCR product to code for the presence of infections and found no instances of parasitemia among the individuals we tested. To confirm that our method of blood storage and processing did not impede our ability to detect infections that were present, we screened 22 Swamp Sparrows (Melospiza georgiana) in Manitoba, Canada, using the same methods, and detected 5 infections. No previous studies have documented a lack of blood parasites in grassland songbirds, but it is possible that this is a result of publication bias against null results. As climate change shifts vector ranges, naïve populations of grassland songbirds may suffer disproportionately if vector presence or parasite transmissibility is altered.

Urbanization is one of the main problems for biodiversity around the world, associated with a decrease of natural habitats and its resources. In contrast, urbanization can also provide new resources that could be used by species that thrive in cities. Understanding why this happens is basic to understand species adaptation to urban areas. Here, we report a nest of a Medium Ground-Finch (Geospiza fortis) built inside a C-purlin beam and artificial materials used for nest building by Medium and Small (G. fuliginosa) ground-finches. The changes that can be observed in some populated areas of the Galapagos Islands, where land cover has been transformed from native habitats into farms, plantations, and urban areas, provide new resources and challenges for native birds and other animals. We discuss the advantages and disadvantages of using artificial materials in nest building and how this may help birds survive in urbanized areas.

We recorded Bushtit (Psaltriparus minimus) flock size on the Seattle University campus across multiple seasons in order to characterize the timing of pair formation prior to nest building in Washington state and compare it to that of California and Arizona. We also collected autumn and winter foraging locations, specifically vegetation types and foraging heights. We found the disbanding of large flocks (15–20 birds) into nest-building pairs occurred 1–2 months later in the northern part of the Bushtit's range than what is reported in more southern states. Bushtits spent a similar percentage of time foraging in deciduous trees, evergreen trees, and mixed shrubs in fall and winter, often moving along garden strips at heights of 3–4.5 m off the ground. Contrary to published reports, groups of Bushtits repeatedly visited fixed food sources, specifically the yellow flowers of the exotic leatherleaf mahonia (Mahonia bealei) for over 2 weeks on early winter mornings.

Alloparenting refers to any type of parental care provided by an individual to non-descendant offspring. Alloparenting is not merely an altruistic behavior; it confers benefits to both care receivers and caregivers. Here, we report 3 cases where 3 adult Great Tits (Parus major) simultaneously provided food to chicks in the same nest boxes during the breeding season of 2019. All 3 cases were found in nest boxes where parent removal experiments were carried out. In our 3 d experiments, one of the parenting adults was temporarily removed from the nest box early on the second day and was back on its nest box at the end of that same day. In 2 of the nest boxes, the 3-adult brood-feeding started upon removing one of the brooding parents and continued on day 3, after the removed adult was returned. In one case, an alloparent was recorded feeding chicks alongside a parent since day 1 and continued feeding chicks on day 2. Our reports are the first documented examples of Great Tits involving a third adult in brooding. It presents an interesting finding for a well-studied bird species and may provide possibilities for in-depth research.

The Alagoas Antwren (Myrmotherula snowi) is a Critically Endangered endemic bird restricted to the Pernambuco Center of Endemism. It is currently restricted to a single forest fragment—the Murici Ecological Station in Alagoas. Its population is currently estimated at less than 30 individuals. Moreover, little is known about the natural history of this species. Since 2010 this bird has been annually monitored, but its nests have never been found. We carried out 131 expeditions to this forest fragment between August 2010 and November 2018. During this period, we captured and marked 11 adults and 7 juveniles. However, it was not until 9 November 2018 that the first nest was discovered. The nest was a deep cup composed of black fungal rhizomorphs with small fragments of dried leaves on the outer side. It was suspended on a horizontal fork of a young plant, 1.7 m above the ground. The eggs were oval in shape, light beige in color with reddish patches distributed throughout the egg and most concentrated in the rhombic pole. The eggs measured 1.53 × 1.02 and 1.54 × 1.03 cm. The nest was monitored, but on 25 November 2018 we found the nest empty; we deduced that it had been preyed upon. Subsequently, we found 3 more nests. However, in our efforts over the most recent 11 expeditions (1 year and 3 months after the original nest discovery until February 2020), we failed to find any additional nests. Our records of juvenile individuals indicate they are still reproducing in the area and represent a possibility to recover this species. However, the strong predation pressure in the area and the absence of mixed flocks are concerning. We urge actions to protect its nests, recompose mixed flocks, translocate individuals to nearby habitat patches, and attempt captive breeding, among efforts that should be evaluated.

Since the mid-1980s, our understanding of avian reproductive strategies has shifted as new molecular technologies have revealed how common promiscuity is in many monogamous avian species. However, the prevalence and importance of extra-pair paternity in polygynous species is less well studied. We used microsatellite loci from related icterid species to identify the extra-pair paternity rate in a polygynous population of Bobolinks (Dolichonyx oryzivorus) that bred in the Champlain Valley of Vermont from 2002 to 2018. We assigned paternity for 120 nestlings and found that 42% of nestlings were sired by extra-pair males. These results highlight the importance of extra-pair paternity in the reproductive behavior of Bobolinks that breed in agricultural habitats.

Polygamy is common in many taxa, particularly birds. Several hypotheses support evolutionary or ecological explanations for the presence of polygamous mating systems, but these may not explain rare occurrences of polygamy in predominantly monogamous systems. We identified 12 cases of polygyny in 3 populations of varying landscape structure (contiguous wildlands, fragmented wildlands, and suburban) across 97 years of collective study on the monogamous Florida Scrub-Jay (Aphelocoma coerulescens). We categorized each case based on social similarities and compared reproduction between monogamous family groups and polygynous males and females. We found no difference in the relative rate of polygyny across the 3 populations. Neither presence of helpers, annual helper sex ratio, or breeder female survival were associated with polygyny occurrence. Reproductive output was similar between polygynous and monogamous males, but significantly lower for polygynous versus monogamous females. Polygyny in Florida Scrub-Jays appears to occur under certain social contexts but is rare even as those contexts are not. Neither sex appears to benefit from polygynous matings but forming a polygynous triad may be better than forgoing breeding.

Acid deposition from fossil fuel combustion caused calcium depletion in eastern North America during the 20th century, and calcium is a critical resource for birds during both the egg laying and nesting periods. The effects of acid deposition on animals have largely acted through trophic relationships, with reduced calcium availability in prey possibly being a limiting factor for forest songbirds. Following 21 years of experimental whole-watershed acidification at the Bear Brook Watershed in Maine, we investigated Ovenbird (Seiurus aurocapilla) territory size and potential prey (leaf litter arthropod) abundance, assemblage, and calcium concentration during one breeding season. We delineated and estimated the area of 8 Ovenbird territories in an acidified and a control watershed, but found that territory size did not differ between watersheds. However, while calcium concentrations of potential prey also did not differ between watersheds, territory size decreased as calcium concentrations of potential prey increased, regardless of watershed. Our results suggest that calcium limitation can be a determinant of territory size in some landscapes, and this provides further support to importance of the role of calcium in the lives of passerines.

Parent songbirds keep their nests clean by removing nestling waste in the form of fecal sacs. Removing fecal sacs is beneficial for the nestlings but energetically costly for the parents. The purpose of our research was to determine whether there was a difference in energy spent on fecal sac removal between male and female Carolina Chickadees (Poecile carolinensis). We collected data for this project at St. Anne Woods and Wetlands in Melbourne, Kentucky, where we made a total of 215 one-hour observations of 30 different nests. For each color-banded parent, we calculated both the number of fecal sac removals and the number of removals divided by the total number of nest visits per hour. Our results showed that males removed more fecal sacs per hour than females. However, this was only because they visited the nest more frequently, as the number of fecal sac removal visits per provisioning visit was the same between the sexes. This suggests that parental energy invested in fecal sac removal is closely tied to their investment in nestling provisioning visits.

Plasticity in bird nest placement is relatively understudied compared to many other aspects of breeding biology. We describe an unusual nest of a Bushtit (Psaltriparus minimus) that was placed inside an old woodpecker cavity instead of being attached to the foliage of a tree or shrub. A pair of Bushtits successfully fledged one brood inside this cavity and then immediately constructed a second nest in the same cavity. Concurrent with this second nesting effort, a Tree Swallow (Tachycineta bicolor) actively competed with the Bushtits for the same cavity and was seen nest building in the cavity as well. The apparent rarity of cavity nesting by the Bushtit suggests this nesting effort was serendipitous and perhaps facilitated by the dimensions of the cavity, which were similar to the hanging, pendulous nest this species typically builds.

Sexual dimorphism may appear in various forms such as anatomical, plumage, or vocal features. Production of such variation can be costly. However, sexual dimorphism may provide long-term fitness benefits. The Sri Lanka Bush Warbler (Elaphrornis palliseri) is a sexually monomorphic and monotypic passerine endemic to the montane cloud forests of the island of Sri Lanka. The iris of this bird shows a marked variation and individuals have either red or ivory-cream colored irises. We studied the iris dichromatism of Sri Lanka Bush Warbler with respect to morphometric and sexual differences. We used PCR-based molecular sexing (n = 8 individuals) and multivariate statistics to analyze morphometric data (n = 20). We found that the iris dichromatism of Sri Lanka Bush Warbler is sex-specific: all females examined (n = 6) had ivory-cream irises and both males examined had bright-red irises, whereas none of the phenotypic traits examined were sexually dimorphic. Our results suggest that the sexual dichromatism observed in this dense understory–dwelling, cloud forest bird might play a central role as a short-distanced optical signal.

We provide an analysis of apparent survival for Inca Dove (Columbina inca) in Galveston, Texas. We aged and banded 24 hatch-year and 103 after-hatch-year doves during 1980–1990. Our analysis provided evidence for effects of body mass on survival. Inca Dove had lower probabilities of apparent annual survival (0.35, SE = 0.04) relative to estimates we found for other species within Columbidae. The annual probability of recapture was 0.87 ± 0.07. Our study's geographic inference space is limited, but our results may provide context for the current expansion of Inca Dove to the north.

Previous intensive surveys on Floreana, the smallest inhabited island of the Galápagos archipelago, in 2015 and 2016, produced reliable population estimates for all landbirds but failed to find 4 species that formerly occurred on the island: Gray Warbler Finch (Certhidea fusca), Vegetarian Finch (Platyspiza crassirostris), Little Vermilion Flycatcher (Pyrocephalus nanus), and Galápagos Rail (Laterallus spilonota). We revisited the island in February 2018 to extend our search to additional areas but again found none of the 4 lost species. As there is no longer any suitable habitat, we are certain that Galápagos Rail is now extinct on Floreana. It is possible that the remaining 3 species still survive in pockets of habitat that have not yet been surveyed. The very distinct subspecies of Gray Warbler-Finch (C. f. ridgwayi) especially merits further investigation.

The Aztec Thrush (Ridgwayia pinicola) is an understudied species. Many aspects of its basic biology are unknown, including its food and foraging preferences. Here, we describe observations of Aztec Thrush consuming fruits of the tree Ilex brandegeeana and flowers of the bromeliad Tillandsia bourgaei in the pine-oak forest of the highlands of Jalisco in western Mexico. These observations provide information about the diet of this species and its possible ecological role in regenerating and structuring processes of this forest.

Evidence of avian predation on Greylag Goose (Anser anser) goslings is generally inferential. Here, we report an observation of a Carrion Crow (Corvus corone corone) preying on a gosling in Port Meadow, Oxford, United Kingdom. Our observation demonstrates that, in addition to being an egg predator, Carrion Crows are opportunistic predators of Greylag Goose goslings. To our knowledge, this is the first time that this interaction has been documented in the literature.