Island birds are often less colorful and sing different songs than their mainland counterparts. Given that trade-offs can occur in the expression of costly sexually selected traits, it is not clear whether island species with less colorful plumage than their mainland counterparts have compensated with increased complexity of song structure. To examine potential trade-offs in sexually selected traits in island birds, we examined concurrent patterns of coloration and song structure in island and mainland (sub)species across 3 widespread and speciose songbird families: Fringillidae, Meliphagidae, and Monarchidae. Phylogenetically controlled analyses revealed a shift away from white plumage and toward melanin-based plumage in island (sub)species but only in the Meliphagidae. Contrary to our predictions, we found no evidence that song structure in island birds differed from their mainland counterparts. Although a number of inverse correlations were identified between song structure and plumage coloration when all birds were considered, this pattern became weaker when only island populations were examined. Instead, we found island size affected song structure leading to a lower number of syllables and lower minimum frequency on smaller islands. Birds on smaller islands also had reduced carotenoid plumage but this pattern was only significant in the Fringillidae. These results indicate that island environments can influence the evolution of both song and color in some taxa, but that selection is tempered by island size, rather than through correlated evolution across signaling modalities.

The Coiba Spinetail (Cranioleuca dissita), endemic to Islas Coiba and Ranchería on the Pacific coast of Panama, was originally classified as a subspecies (C. d. dissita) of the geographically distant Rusty-backed Spinetail (C. vulpina) of South America, but its status has long been an enigma. The present study was conducted to obtain basic information on the ecology, behavior, and vocalizations of this species, which has previously been lacking. On both islands, Coiba Spinetail was found almost exclusively in forest and forest edge. Their most common foraging substrate was small-diameter (∼1 cm) branches or vines, although they also foraged on tree trunks. The foraging type most often observed was pecking, but probing and gleaning were also observed regularly. The most common foraging height was 7–10 m above the ground, although they foraged as low as 2 m and as high as 25 m. The nest of Coiba Spinetail, which has not been previously described, is a globe-shaped structure made mostly of plant fibers and built around a vertical support such as an upright branch or trunk or around several lianas or vines. The nest of Rusty-backed Spinetail instead is a globular mass of grass, roots, and sticks, wedged in the fork of a partly submerged sapling or bush. The song of Coiba Spinetail resembles typical Cranioleuca spp. in having several short introductory notes followed by a series of notes on one pitch. It differs from most species in the genus, however, in that the notes gradually become longer and slow down, rather than accelerating or being evenly spaced. The song differs markedly from that of Rusty-backed Spinetail in note structure and quality. These results coupled with previous findings that Coiba Spinetail is genetically distinct from Rusty-backed Spinetail indicate that it merits full species status. Considering its extremely small range, Coiba Spinetail qualifies for Near Threatened status under IUCN Red List criteria.

Many passerines regularly use flight calls to communicate during migration. However, flight-calling is inconsistent throughout the day, with a markedly lower degree of calling by free-flying individuals during the early evening hours and with peaks in calling typically around dawn. Based on these observations, we hypothesized that individual flight call response would vary by time of day, and the likelihood to respond would be lower at dusk than during the daytime. We tested daytime and dusk flight call responsiveness of captive American Redstarts (Setophaga ruticilla) and Magnolia Warblers (S. magnolia) during spring migration at the Braddock Bay Bird Observatory (near Rochester, New York, USA). We played a conspecific flight call sound stimulus for individual birds placed inside a soundproof recording studio and recorded their acoustic responses. In our experiment, American Redstarts and Magnolia Warblers were significantly less likely to give flight call responses at dusk than the individuals tested during the daytime. The almost absent responsiveness to flight calls at dusk suggests that these species either minimally communicate with one another during take-off or do not use flight calls as a source of communication at this time. These results have important implications for detection and quantitative bioacoustics migration monitoring. They also demonstrate the need for additional studies in temporal flight-calling behavior.

We studied plumages and molt patterns of Yellow-bellied (Empidonax flaviventris), Least (E. minimus), and Alder (E. alnorum) flycatchers, primarily on the breeding grounds but with additional data from wintering grounds and a migration stopover site, in order to clarify our knowledge of molt strategies in these species. We determined that these 3 species have a similar overall molt strategy: (1) a partial-to-incomplete preformative molt begun on the breeding grounds, suspended over migration, and completed on the wintering grounds; (2) a limited-to-partial first prealternate molt on the wintering grounds that can overlap the final stages of the preformative molt; (3) a complete definitive prebasic molt begun on summer grounds and completed on wintering grounds; and (4) a limited-to-partial definitive prealternate molt that may overlap with the final stages of the prebasic molt. Our study clarifies previous terminologies and allows these molts to be interpreted in an evolutionary framework. We suggest that observed differences in molt extents among species may be linked to differences in wintering latitude and habitat. The broadleaf forest preferred by Yellow-bellied Flycatcher likely retains insect biomass later into the winter season than the scrub habitat preferred by Least Flycatcher, and this may promote more extensive preformative feather replacement in that species. The much more extensive preformative molt of Alder Flycatcher may be due to its wintering farther south, where there is greater annual solar exposure, perhaps resulting in higher rates of feather degradation. Our data also suggest that the extent of prealternate molt in these species may vary with proximate factors on the winter grounds affecting individuals, rather than body condition at the beginning of winter.

It is estimated that about 80% of North American avian migrants travel along the southern coast of Texas. Quality of stopover habitat for landbirds in southern Texas is a concern, however, due to agricultural and wind energy development and increasing urbanization. Since little regional research has been conducted on stopover habitat use, we investigated habitat associations of migratory birds to identify important factors driving density along the southern Texas coast. We did this using data from landbird surveys, which took place during spring and autumn migrations from 1991 to 1993 and 2006 to 2008, within 6 land-cover types common in southern Texas. We found that oak motte had the highest density among most bird guilds. A total of 125 species of birds were detected over the course of our study and species richness was highest in oak motte and lowest in grassland. In general, land-cover types with more woody vegetation cover tended to have higher species richness and diversity than those with minimal to no woody vegetation. Although grassland ranked lowest in other metrics of bird use, it ranked highest in habitat conservation value, which accounts for species of concern. At the time of this study, Golden-winged Warbler (Vermivora chrysoptera) was the only species on Partners in Flight's Red Watch List (highly vulnerable and in need of special attention) that we observed, with recorded observations occurring in oak motte and woodland exclusively. Oak mottes are likely a prime location for species to land after flying over the Gulf of Mexico during their journey north to their breeding grounds, thus land managers that wish to provide high-quality stopover sites for migratory landbirds should preserve them.

Shorebird use of horseshoe crab (Limulus polyphemus) eggs as food items has been well documented along the Atlantic coast of the United States at northeastern stopover sites such as the Delaware Bay. However, the relationship between migratory shorebirds and horseshoe crab eggs has not been well studied in the South Atlantic Bight. The objective of our study was to assess the spatial and temporal overlap between the density of horseshoe crab eggs and the relative abundance of foraging shorebirds during spring migration in the Cape Romain-Santee Delta Region (CRSD), South Carolina, USA. The CRSD is a site of international importance for shorebirds that supports ∼100,000 shorebirds annually. We also sought to determine if horseshoe crab eggs were present in the diets of shorebirds at these sites. We monitored study plots between March and June 2015–2016 at predicted horseshoe crab spawning sites on beaches throughout Cape Romain National Wildlife Refuge. We conducted weekly shorebird surveys and collected core samples of beach substrate twice per month to measure densities of horseshoe crab eggs. We found a positive correlation between number of foraging shorebirds and horseshoe crab eggs for both years. In a molecular analysis of shorebird fecal samples, 95% of the samples tested contained DNA from horseshoe crab eggs. The spatial and temporal overlap between shorebirds and horseshoe crab eggs, and the dietary analysis of fecal samples, suggest that there are areas of localized horseshoe crab spawning that shorebirds can utilize as a food source during spring in Cape Romain National Wildlife Refuge.

Great-tailed Grackle (Quiscalus mexicanus) and Common Grackle (Q. quiscula) are phylogenetically distant among grackles and were historically allopatric. Northward range expansion of Great-tailed Grackle and westward expansion of Common Grackle brought these species into increasing contact over the past century but has not led to notable interactions. Hybrids of Great-tailed Grackle with Boat-tailed Grackle (Q. major), Brewer's Blackbird (Euphagus cyanocephalus), and Red-winged Blackbird (Agelaius phoeniceus) have been reported, whereas hybridization of Common Grackle has never been documented with any species. We report a brood of 2 hybrid offspring of a male Great-tailed Grackle and female Common Grackle in Dillon, Montana, in 2015. For about a week after their discovery, both parents defended and fed the fledglings, the latter behavior extraordinary for a male Great-tailed Grackle. Moreover, whereas the female parent was no longer seen, the male continued to feed the young for at least another 7 weeks after they left the nest tree, during which time the trio moved ∼2 km across town and the young began prebasic molt, growing iridescent blue-black secondary coverts as expected for male Great-tailed Grackle but not for Common Grackle or female Great-tailed Grackle. Analysis of DNA from a feather of one offspring confirmed that it had hybrid nuclear DNA, had Common Grackle mitochondrial DNA, and was male. In 2016, the male Great-tailed Grackle again courted a female Common Grackle that nested in his tree, a nest which he defended, but she was also attended by a male Common Grackle. She produced 5 young, all of which were genetically pure Common Grackles, not hybrids. Also notable in 2016, another male Great-tailed Grackle in the general vicinity was observed feeding young in 1 of 3 nests that he defended, suggesting that male parental care may be more common in that species than has been appreciated.

Hybridization can have profound effects on biological diversity. However, predictable inheritance of plumage traits remains poorly understood, especially for rare hybrids. We reviewed the literature and compiled a comprehensive list of hybrids from the New World warbler family Parulidae, a diverse radiation of songbirds with divergent plumage traits. We used our compilation to analyze modes of inheritance in wing bar patterns and carotenoid coloration. Finally, we describe an unusual hybrid from the University of New Mexico in Albuquerque, New Mexico, southwestern USA. We identified evidence of hybridization in 44 of 47 (93%) North American parulid species, with the highest number of hybrids found in the genus Setophaga. Plumage patterns between hybrid offspring and parental forms in our 2 focal traits were predictable, supporting the identification of our hybrid as a Yellow × Black-throated Blue Warbler (S. petechia × S. caerulescens). We based our identification on the extent and pattern of white in the tail, a prominent white wing flag, and our ability to confidently rule out all other alternative parentals. Our results suggest that phenotypes of rare hybrid warblers likely have some degree of predictability.

Predation on vertebrate species by insect-eating birds is rarely recorded, with only one report for the House Wren (Troglodytes aedon). On 4 January 2019, we observed a Dominican House Wren (T. a. rufescens) consume a juvenile of the nonnative Puerto Rican crested anole (Anolis cristatellus) in Roseau, Commonwealth of Dominica. This observation suggests the Dominican House Wren could additionally prey on the endemic Dominican anole (Anolis oculatus). This record aids our understanding of the ecosystem-wide impact of the A. cristatellus invasion.

Nest microclimate can be affected by wind and solar radiation, which can influence offspring survival. The endangered Florida Grasshopper Sparrow (Ammodramus savannarum floridanus) constructs a domed nest on the ground in dry prairie and pasture habitats of central Florida. We measured the nest opening orientation for 116 Florida Grasshopper Sparrow nests across 2 sites with different habitats (2014–2016). Nest openings were primarily oriented to the northeast and orientation did not differ by site. Nest opening orientation did not influence the probability that a nest would successfully fledge at least 1 nestling. It is possible that Florida Grasshopper Sparrows may orient nests to the northeast to avoid wind-blown rain from summer storms and solar radiation during the hottest part of the day, but high local rates of nest predation documented at both sites mask the selective advantage of nest orientation on nest survival.

The reproductive biology of tropical hummingbirds has been documented and studied in only a small fraction of species relative to the great diversity of this group. Little has been written about breeding biology of hummingbirds at the Northern Andes Eastern Cordillera in Colombia. We present detailed information on the dates, nesting locations, construction materials, measurements of nests and eggs, and gonad development of adult specimens to augment the scant reproductive data available of 2 widely distributed highland hummingbirds, the Tyrian Metaltail (Metallura tyrianthina) and the Glowing Puffleg (Eriocnemis vestita). These data were obtained during multi-taxa collection expeditions in the high-elevation region of the Department of Boyacá, Colombia. We found 2 Tyrian Metaltail nests in February and May, and adults with enlarged gonads in August. The single Glowing Puffleg nest was found in October, adults with enlarged gonads in May and October, and a chick mortality event (possibly due to frost) in November. Nesting sites for both species were in banks where they built 2-layered cup nests. Although nest locations and construction materials were similar to what has been reported before for hummingbirds in these genera, we identified the plants of these nests' microhabitats, as well as the families and genera of liverworts, mosses, and others used as nest construction materials. The evidence of active nests and enlarged gonads of specimens collected in this study, together with observations made by previous authors, suggest that these 2 hummingbird species breed throughout most of the year at the northeastern Andes. Our data contributes to the understanding of the reproductive biology of these hummingbirds in this region.

Nest predation is the primary cause of nest failure in passerines. In order to contribute to our understanding of how nest predators shape avian nesting ecology and life history traits, we report nest predator identity and nest predation rates for 3 species of passerines in the Central Andes of south temperate Argentina. We used video cameras and opportunistic observations with photographic documentation to identify nest predators of Grass Wrens (Cistothorus platensis) breeding in a riparian grassland, as well as House Wrens (Troglodytes aedon) and House Sparrows (Passer domesticus) breeding in nest boxes in a tree plantation. From 13 nest predation events we were able to identify 3 nest predator species: mousehole snake (Philodryas trilineata), South American gray fox (Lycalopex griseus), and American Kestrel (Falco sparverius). Field observations also suggested fire ants (genera Solenopsis) as a possible nest predator. Mousehole snakes were identified at both grassland and forest plantation, representing 76.9% of the identified predation events. House Sparrows had the highest nest predation rate (43.1%), followed by Grass Wrens (30.8%) and House Wrens (29.3%). Egg predation was more frequent for House Wrens (64.2%) and House Sparrows (50.0%) than for Grass Wrens (22.1%). In contrast, nestling predation was considerably higher for Grass Wrens (77.9%) than for House Wrens and House Sparrows (34.7% and 50.0%, respectively). Knowledge of the nest predator community and information of nest predation rates of different species in temperate South America will contribute to understand nest predation effects on patterns and processes of nesting success, life history traits, and future management decisions in this region.

The Least Tern (Sternula antillarum) commonly breeds along coastal beaches and major interior rivers of North America and the Caribbean. Least Terns have been observed in Hawai‘i since the 1970s; however, few breeding attempts have been documented. Nests have been discovered on the northwestern Hawaiian island of Midway Atoll and the southeastern Hawaiian island of Hawai‘i. While nesting is thought to also occur on the islands of O‘ahu and French Frigate Shoals based on observations of juvenile Least Terns, no observations of nests had been recorded for these islands prior to this study. In this paper we describe 2 accounts of discovering Least Tern eggs in the Ki‘i Unit of the James Campbell National Wildlife Refuge on O‘ahu, as well as several observations of breeding behavior in wetlands within the Pearl Harbor region of O‘ahu.

Adult animals across many taxa use appeasement signaling to minimize or avoid costly conflict in social settings by jointly communicating their consent to defer and an interest to remain. When foraging, however, appeasement may not be enough to gain access to a resource controlled by a dominant conspecific. In this case, conspecific recruitment can shift the social dynamic, so the resource becomes accessible to all. Striated Caracara (Phalcoboenus australis) are Near Threatened scavenging falconids that breed in high densities on the extreme southern coasts of South America and the Falkland Islands. While juvenile caracaras recruit other caracaras to concentrated food resources, neither recruitment nor appeasement has been reported in adults. Here we describe a female adult caracara that appeared to use both appeasement signaling and recruitment to access food in another pair's defended territory on New Island, Falkland Islands. Appeasement and recruitment calls are one of several behavioral parallels that researchers have noted among Striated Caracara, Common Raven (Corvus corax), and Kea (Nestor notabilis). Although falconids are not typically considered in comparative studies of avian cognition and social behavior, we suggest that caracaras merit further attention, especially given their relationship to parrots in the clade Eufalconimorphae.

For a second decade, from November 2008 to March 2018, we examined the species diversity, return rate, longevity, and migration routes of hummingbirds overwintering in southern Alabama and the panhandle, northern peninsula, and central peninsula of Florida. We captured and banded 11 species of hummingbirds (n= 1,870 individuals), including 931 Rufous Hummingbirds (Selasphorus rufus; 49%), 583 Ruby-throated Hummingbirds (Archilochus colubris; 31%), 219 Black-chinned Hummingbirds (A. alexandri; 12%), 49 Buff-bellied Hummingbirds (Amazilia yucatanensis), 49 Calliope Hummingbirds (S. calliope), 19 Allen's Hummingbirds (S. sasin), 11 Broad-tailed Hummingbirds (S. platycercus), 6 Broad-billed Hummingbirds (Cynanthus latriostris), 1 Anna's Hummingbird (Calypte anna), 1 Costa's Hummingbird (Calypte costae), and 1 White-eared Hummingbird (Hylocharis leucotis). Site fidelity was high, with 299 hummingbirds of 5 species returning at least once. Two Rufous Hummingbirds migrated to our study area in the autumn from the West (Oklahoma and Texas). One Ruby-throated Hummingbird banded in Lakeland, Florida, was recovered in Utopia, New Brunswick, Canada, suggesting the overwintering Ruby-throated Hummingbirds in our study area are migratory and not sedentary.

A mass die-off of Common Murres (Uria aalge) occurred from spring 2015 to spring 2016 in the northern Gulf of Alaska. Seabird die-offs have been recorded previously in the region, but this event was unique in its long duration and wide spatial extent. In response to the die-off, Kodiak National Wildlife Refuge (NWR) biologists conducted systematic beach surveys along the road system adjacent to the city of Kodiak and compiled reports from local citizens in remote locations throughout the Kodiak Archipelago to document the number of dead birds observed on beaches. Analysis of beached bird records indicated that at least 1,994 dead Common Murres were observed in the Kodiak Archipelago from 4 April 2015 to 26 April 2016. Extrapolating the density estimate, based on carcasses counted on systematic surveys on the Kodiak road system (55 murres/km, SE = 12), to all beaches in the Kodiak road system study region in the same biophysical habitat class based on Alaska ShoreZone coastal mapping, yielded an estimate of 6,305 dead Common Murres (95% CI = 3,522–9,088). In addition to Common Murres, carcasses of another 65 birds representing 15 species were found on beaches on the Kodiak road system during the die-off. The die-off event was preceded by a large-scale inshore movement by marine bird species typically seen offshore (Common Murres and shearwater species), as documented by Kodiak NWR survey data and by local observers throughout the archipelago. Survey data indicate the population estimate for Common Murres in the northeastern region of the archipelago increased from 711 in June 2012 to 31,543 in June 2015 (4,335% increase), and from 5,063 in August 2012 to 64,039 in August 2015 (1,165% increase).

Predators eavesdropping on prey communication is relatively little studied. Oriental Tits (Parus minor) use “jar” alarm calls toward snake predators near their nests. In response to this call, nestlings fly out of the nest if they are old enough to fledge. After fledging, chicks are vulnerable to predation by corvids. Here we present field observations consistent with the idea that corvids may be attracted to the “jar” alarm calls because these calls predictably trigger fledging of nestlings making them available as prey. Controlled field experiments should test this idea in the future.

We present the first record of plumage color aberration and the occurrence of slow-growing feather tissue in the Painted Bunting (Passerina ciris), a colorful songbird breeding in the southern United States during summer and migrating to Central America in winter. We took advantage of this rare sampling opportunity and performed hydrogen stable isotope analysis on 12 cross-sections of 2 primary feathers to compare isotopic values in normal and aberrant tissue sampled from the same individual. We used feather hydrogen stable isotope variation as an informative environmental marker to track the movements of the bird across its annual cycle. Spatial probability density estimates suggest further movements after this bunting arrived at molting stopover sites in northern coastal Mexico, either migrating toward southern coastal latitudes or toward higher elevations. Although we are unable to definitively assign a cause to the aberrant feather and its slow growth rate, we highlight how combining the observation of an atypical morphological trait with a modern molecular approach offers an opportunity to advance our understanding of avian movement behavior.

Egg size is a useful metric for maternal investment, offspring quality, and contaminant studies. Yet these values and the egg shape coefficients required to estimate egg size are not available for many species, including White-faced-Ibis (Plegadis chihi). We provide egg morphometrics derived from 319 White-faced Ibis eggs sampled at Bear River Migratory Bird Refuge, Great Salt Lake, Utah, from 2010 to 2012. Measured egg length (mean ± SD) was 51.20 ± 1.99 mm, egg width was 36.08 ± 1.15 mm, and whole egg mass was 34.1 ± 3.3 g. Estimated whole egg volume was 34.63 ± 3.73 cm³ and estimated egg shape coefficients were 0.507 for K_v (whole egg and egg contents), 0.547 for K_w (whole egg), and 0.524 for K_w (egg contents only). In addition, we documented expected declines in egg mass over time due to incubation (–0.22 g/d) and desiccation during storage (–0.03 g/d), that should be accounted for prior to analyses that use egg mass of freshly laid eggs.

In a recent publication, examined responses of territorial male Red-winged Blackbirds (Agelaius phoeniceus) to models constructed with ultraviolet (UV)-reflective red epaulets for the purpose of determining if the addition of UV reflectance to epaulets (“UV+”) changed the effectiveness of signals to receivers relative to “control” epaulets under field conditions. The authors hypothesized that “UV+epaulet coloration represents a visual signal with increased efficacy in territorial interactions.” They presented behavioral data but no visual modeling data. Our aims in this commentary are to suggest alternative terms to those used by the authors, to express concern about the use of sunscreen to manipulate the UV condition of surfaces, and to make a plea for additional data collection in future studies of avian visual ecology. The terms UV+ and UV– should be reserved for studies that create environments free from UV radiation for comparison with environments that include UV radiation. We believe that commercial sunscreens are not an appropriate choice for altering the UV conditions of surfaces presented during behavioral trials because they potentially introduce confounding influences from other sensory inputs or irritation of peripheral nerves. Wisenden et al. altered the UV absorbance of their sunscreen-treated models but did not present absorbance spectra and may not have collected those data. We acknowledge that the lack of absorbance spectra is not unusual. We implore any such future studies to collect absorbance spectra of treated and control surfaces so that those data may be used to improve visual models for UV-sensitive animals.

reported differential behavioral responses by male Red-winged Blackbirds (Agelaius phoeniceus) to models bearing a red-epaulet visual signal with and without reflectance in the ultraviolet (UV) portion of the spectrum. wrote a response, claiming that some of our key terminology was incorrect and that our methodology was potentially confounded, calling into question the veracity of the results reported in our study. Herein, we explain (1) our use of the term “control” to be the treatment that lacks the test variable of interest; (2) the labels UV+and UV–refer to treatments that did, and did not, reflect in the UV; (3) that sunscreen likely did not contain methyl anthranilate, and even if it did, the amounts of sunscreen used were so small that it could not possibly explain the behavioral effects we observed over the distances between models and territorial males tested in the field; and (4) visual modeling would not enhance the interpretation or impact of our study. We do agree with that additional field research should be done to better understand visual ecology and the evolution of avian plumage signals.