This perspective on the stopover biology of migratory landbirds is organized around the response of migrants to challenges that can arise during stopover and how events during stopover are interconnected with other phases of the annual cycle. Landbird migrants seldom move nonstop from origin to destination, rather they stopover periodically, sometimes for a few hours, sometimes days. How well migrants meet challenges that arise during passage in a timely manner influences the success of their migration; a successful migration is measured in terms of survival and reproductive performance over the annual cycle. What transpires during migration is not isolated from other phases of the migrant's annual cycle. Events taking place in one phase carry over to affect an individual's biology in other phases, including linkage between breeding and wintering phases and the intervening migratory phase.

Predictive species distribution models and environmental niche evaluation have become useful techniques in conservation biogeography and are increasingly used as prediction tools to identify priority conservation areas for focal species. Multiple hypotheses and paradigms were proposed to explain the variation seen in geographical range sizes among species. Our hypothesis was that in a monophyletic group of 7 Campylorhynchus species, those with a broad climatic niche would persist over a wide geographic range while species with a narrow climatic niche, such as C. yucatanicus, would be restricted to a smaller geographic range. To test this hypothesis, we modeled potential distributions using the MaxEnt algorithm and estimated the climatic niche of 7 species included in the monophyletic group of Campylorhynchus (Troglodytidae). To compare the ecological niches of these 7 species, we plotted the occurrence density for each species with combinations of environmental conditions and then identified the first 2 components using a principal component analysis. In general, the most important variables predicting species presence were rainfall seasonality and minimum temperature during the coldest month. The climatic niches for these 7 species were relatively segregated throughout the environmental space. When compared with related species, C. yucatanicus had the narrowest niche width and lowest niche similarity and overlap index, which could explain the restricted distribution for this species. Given the restricted range of C. yucatanicus within the Yucatan Peninsula, the species is highly vulnerable to small disturbances, current local threats (e.g., habitat alterations due to urbanization), and global threats (e.g., climate change). We therefore recommend increased national and international protection for C. yucatanicus and that it be listed as globally threatened by the International Union for Conservation of Nature (IUCN). Received 22 June 2016. Accepted 9 June 2017.

We described past and present distribution and abundance data to evaluate the status of the endangered Mariana Swiftlet (Aerodramus bartschi), a little-known echolocating cave swiftlet that currently inhabits 3 of 5 formerly occupied islands in the Mariana archipelago. We then evaluated the survey methods used to attain these estimates via fieldwork carried out on an introduced population of Mariana Swiftlets on the island of O'ahu, Hawaiian Islands, to derive better methods for future surveys. We estimate the range-wide population of Mariana Swiftlets to be 5,704 individuals occurring in 15 caves on Saipan, Aguiguan, and Guam in the Marianas; and 142 individuals occupying one tunnel on O'ahu. We further confirm that swiftlets have been extirpated from Rota and Tinian and have declined on Aguiguan. Swiftlets have remained relatively stable on Guam and Saipan in recent years. Our assessment of survey methods used for Mariana Swiftlets suggests overestimates depending on the technique used. We suggest the use of night vision technology and other changes to more accurately reflect their distribution, abundance, and status.

The incidence of extra-pair paternity (EPP) is highly variable across bird taxa. While EPP is known to affect reproductive variance, the causes of temporal variation in rates of EPP are poorly studied. Breeding density has often been proposed as an important factor influencing EPP variation, but it has received mixed support. Over a 5-year period we examined the rate of EPP in a socially monogamous Grasshopper Sparrow (Ammodramus savannarum) population on a restored grassland in Maryland. Of 124 broods, 62.1% had extra-pair young (EPY), and of 448 nestlings, 36.8% were the result of extra-pair fertilizations. Over the 5-year study, percent EPY ranged from 26% to 60%. EPP rates were positively correlated with the local density of territorial males, supporting the density hypothesis, and 81% of the EPY were from neighboring males. Male within-pair mating success was related to extra-pair mating, suggesting an active behavioral tradeoff between within- and extra-pair matings, especially at high densities. By examining males at the individual level, we found males that were not cuckolded also had the most genetic offspring (within-pair and extra-pair), whereas males that were cuckolded also failed to sire many extra-pair offspring. Here we show that density plays an important role in the availability of mates, EPP, and the opportunity for sexual selection. Received 9 April 2016. Accepted 3 August 2017.

Contemporary knowledge of migrant waterfowl chronologies is important for effective population management, especially in the context of shifting phenology and climate change. We used a dataset of year-round, every other week, comprehensive bird counts during 2002–2013 on a 461 ha island of shallow water impoundments in central Chesapeake Bay to define the migration period for 21 species of surface and diving waterfowl. Migrant periods for species going north ranged from 7 January through 31 May, with nearly all species reaching a mean date during 19 February through 23 March. South migrant periods ranged from 1 August through 12 February, with most experiencing a mean date during 23 October through 8 January. The migration period average for both surface and diving species was 7 d longer going north than south, whereas both the north and south surface species migration period averages were 15 d longer than the diving species. We found significant differences (P < 0.001) among the migration periods of many individual species. When comparing the 2002–2013 migration period mean date with pre-1958 peak migration periods, we found 14 species are now arriving north earlier, south later, or both, which could be attributed to various factors, including warming temperatures on northerly breeding grounds. Results from this study provide definitive migrant waterfowl chronologies for species commonly traversing the mid-Atlantic area and are the first available for that region in more than half a century. Received 25 March 2016. Accepted 14 July 2017.

We combined data on morphology, behavior, and gene sequences to document the first known case of hybridization within the thrush genus Catharus. During June 2008 at a montane forest site in south-central Vermont, we observed a male bird that repeatedly exhibited song characteristics of both Bicknell's Thrush (C. bicknelli) and Veery (C. fuscescens). Handheld examination determined the bird to be a yearling male with plumage characteristics predominantly of Veery and morphometric traits within the ranges of both Bicknell's Thrush and Veery. While the hybrid vocalized only with Bicknell's Thrush calls, its songs were reminiscent of both Veery and a mixture of Bicknell's Thrush and Veery. Mitochondrial DNA (NADH dehydrogenase 2 and cytochrome b genes) revealed the bird's mother to be a Veery, and nuclear data (β-fibrinogen 7 and myoglobin 2 introns) revealed DNA of both Veery and Bicknell's Thrush, supporting Bicknell's Thrush as the father of the hybrid. This hybridization is notable given that Bicknell's Thrush and Veery generally breed in different habitat types at different elevations. This discovery is also important in light of the vulnerable conservation status of Bicknell's Thrush and recent declines in Veery populations across much of the species' breeding range.

Studying the anthropogenic components of landscapes can provide a solid groundwork to better understand ecological patterns and processes. In this study, we assessed bird species richness and composition in 5 different environmental conditions (well-preserved cloud forest, peri-urban forest, urban greenspace, shade coffee plantation, and cattle ranch) embedded in a landscape whose original vegetation was tropical montane cloud forest. Our results showed that the most similar vegetation structure and physiognomy were peri-urban forest and shade coffee plantation, with urban greenspaces comprising a highly different condition. Regarding species richness, we found no differences for the nonbreeding season (average values 32.9–41.8), but we did find statistical differences for the breeding season (average values 24.5–43.7); highest species richness was recorded for well-preserved cloud forest (43.7 calculated species), which was significantly different from shade coffee plantation (lowest species richness value 24.5) and urban greenspaces (29 calculated species). These results support the idea that during the nonbreeding season, when habitat requirements are less strict, species distribute homogeneously across the landscape, whereas species tend to be more selective and concentrated in original forests during the breeding season. Community composition during the breeding season showed a >40% similarity cluster composed of well-preserved cloud forest, shade coffee plantation, and cattle ranch. In the nonbreeding season, however, 2 clusters were formed at ∼30% similarity: (1) urban greenspaces and cattle ranch; and (2) peri-urban forest, shade coffee plantation, and well-preserved cloud forest. Our results highlight the overall negative effect of urbanization on breeding bird species richness and composition, as well as the importance of having large patches of well-preserved cloud forests in sheltering high bird diversity.

Amazonian bird species often have patchy spatial distributions, and previous work has attributed this pattern to habitat specialization and dispersal limitation; however, we know comparatively little about the origins and maintenance of the isolated populations that constitute a patchy distribution. In this study, we ask whether patchy populations are interconnected by dispersal. We formulated 2 alternative hypotheses: (1) patchy populations are relicts of ancient connectivity or dispersal; and (2) patchy populations are centers of local abundance embedded in a matrix of contemporary dispersal or diffuse intervening populations. We confronted these hypotheses with circumstantial evidence derived from a unique suite of noteworthy bird records and geological observations from northeastern Peru. We found support for both hypotheses in different species, and sometimes within single species at different spatial scales. Phenotypically differentiated populations in relictual habitat patches provide strong support for the first hypothesis, whereas populations in recently created, ephemeral habitat patches provide strong support for the second. Colonizations of anthropogenic habitats are further examples of the second process, and they indicate ongoing changes in the porous connectivity of upper Amazonia. These results highlight the need for a conservation approach that accounts for metapopulation dynamics across patchy species ranges.

In Southeast Asia, some plantation developers have retained patches of native forest within plantations to promote wildlife diversity, but relatively few studies have examined the effectiveness of such efforts. To provide more information on the interaction between native forest and plantation, we conducted surveys of birds in patches of logged native forest and surrounding groves of exotic plantations in Borneo. We asked the following questions: Does plantation age influence the bird community in adjacent native forest fragments? Are bird communities in the plantations influenced by the presence of small fragments of native forest? Are bird communities in more intensively managed plantations different compared to less intensively managed plantation? Do bird distributions across habitat types vary by functional trait? Our study was conducted in a 500,000 ha multi-use landscape in Sarawak, Malaysia. We identified 15 native forest fragments within exotic plantation, and these were partitioned into old (>7 yr) and young (<5 yr) groves. We conducted surveys in the native forest fragments and in the 2 age groups of adjacent plantation at distances near (<500 m) and far (>500 m) from fragments. Species richness was highest in native forest fragments. In plantation groves near fragments, species richness remained comparable to native forest but dropped significantly in young plantation far from fragments. The International Union for Conservation of Nature (IUCN) threat status was significantly related to species habitat associations, with Near Threatened species preferring native forest. Although protecting large tracts of native forest is optimal for protection of birds, smaller patches may also maintain considerable levels of species richness in plantations, and they may be particularly important during the early phases (first 5 yr) of plantation growth.

In resident Amazonian mixed-species flocks, the pattern of attraction of transient species to nuclear Dusky-throated Antshrikes (Thamnomanes ardesiacus) and Long-winged Antwrens (Myrmotherula longipennis) and the pattern of heterospecific attraction between the nuclear species are undocumented. Patterns of attraction can help elucidate the nature of interspecific relationships (i.e., whether they are mutualistic, commensal, or parasitic). We played Dusky-throated Antshrike and Long-winged Antwren vocalizations to flocks and recorded how many transient species approached the playbacks, whether the antshrikes and antwrens were attracted to each other's playbacks, and how strongly they responded to the playbacks. More transient species were attracted to the antshrike vocalizations than antwren vocalizations, and more transient species were attracted to antwren than control vocalizations. Dusky-throated Antshrikes and Long-winged Antwrens approached each other's playback significantly more often than they approached control playbacks; the antwrens responded significantly more strongly to antshrike vocalizations than the antshrikes did to antwren vocalizations. Species may be more attracted to Dusky-throated Antshrikes because of their reliable alarm calling, whereas species may be attracted to antwrens because they serve as a flock indicator. Finally, Dusky-throated Antshrikes and Long-winged Antwrens likely confer benefits to each other, but those benefits may not be symmetrical.

Interannual mate and site fidelity is common in migratory shorebirds with monogamous mating systems. After long-distance migrations and separation during the winter, birds often relocate their former mate at their previous breeding territory. Although pairs frequently reunite, new pairs are also formed. Why birds change mates is still not completely understood. Mate change can involve active decisions, in which one or both mates actively chooses to divorce from a previous mate, but can also be related to arrival timing or mate availability at the breeding grounds. We explored possible causes of mate change in the Pacific subspecies of the migratory shorebird Dunlin (Calidris alpina pacifica) breeding at the subarctic Yukon-Kuskokwim Delta, Alaska, USA (61°36′N, 165°12′W). Interannual return rates of Dunlin to their breeding grounds were higher for males (74%) than for females (54%) and were 14% higher for birds with high previous breeding success. Mate change was rare if both birds returned to the breeding grounds in a consecutive breeding season: only 8% of all pairs divorced when previous mates were available. When former mates failed to return or returned late, however, many individuals formed new pairs (45% of males and 53% of females). Nest initiation dates were not delayed for new pairs compared to reuniting pairs, and nest survival did not differ between new and reuniting pairs; however, renesting after nest failure within a season was faster for reuniting pairs. We conclude that avoiding delayed nesting is a strong determinant of breeding decisions in Pacific Dunlin nesting in the short subarctic summer.

The Rusty-breasted Antpitta (Grallaricula ferrugineipectus) is widely distributed within the tropical Andes of South America. We analyzed 73 study specimens, 25 vouchered tissue samples, and 123 audio recordings to assess geographic variation in genetics, vocalizations, and morphology and evaluate species limits. We found that Grallaricula ferrugineipectus as currently defined is polyphyletic because populations from Colombia and Venezuela form a clade closely related to Andean populations of G. nana, whereas populations from Peru and Bolivia are recovered as sister to G. lineifrons. Birds in Colombia and Venezuela (the northern group) last shared a common ancestor with birds from Peru and Bolivia (the southern group) more than 10 million years ago. Northern and southern groups additionally differ in song, suggesting they may have evolved substantial premating reproductive isolation. Discriminant function analysis reliably distinguished songs from northern and southern groups in multivariate acoustic space, but univariate analyses found non-overlapping acoustic variation between northern and southern groups in only one trait: mean note maximum frequency (and other correlated measures of song pitch). This finding suggests that the ‘three-trait' threshold for using vocalizations to inform species limits, which was developed for another suboscine group, the antbirds (Thamnophilidae), may be conservative when applied to antpittas (Grallariidae). In addition, we document apparent clinal variation in song pace within the southern group, a rare example of a suboscine with geographic clinal variation in a vocal trait. Finally, we show that northern and southern groups differ markedly in morphology. In summary, northern and southern groups of Rusty-breasted Antpittas are divergent in genetics, vocalizations, and morphology, demonstrating that these taxa are best classified as 2 monophyletic, biological species with allopatric distributions.

In this study I examined heterospecific eavesdropping in passerines by investigating how information broadcast by the Tufted Titmouse (Baeolophus bicolor) at dusk modifies singing and calling vocalizations of a common avian dusk chorus species, the Veery (Catharus fuscescens). The Veery nests on or near the ground and is a highly vocal participant of the avian dusk chorus, which also renders it vulnerable to a wide array of diurnal and crepuscular predators. Thus, the Veery is expected to be sensitive to signals of predation risk. Here, I report findings of simulated exposure to indirect predation risk (recorded playbacks of Tufted Titmouse alarm calls) that alter acoustic output by the Veery. From 19 May to 6 July 2013, 14 plots in Veery territories were selected and exposed to playback calls of the gray tree frog (Hyla versicolor; control treatment) and playbacks of the Tufted Titmouse high seet call (experimental treatment). Each plot was subjected to two 65 min playback-recording trials (one experimental and one control); Veery song and call output were quantified via spectrograms to compare Veery acoustic response between treatments. The Veery produced a greater call output while song output remained unchanged between control and experimental treatments. These results reveal that the Veery indeed detected and responded to heterospecific alarm calls. Moreover, the Veery acted as a secondary community informant, further transmitting information regarding predation risk to conspecifics and the dusk chorus community at large.

Parental provisioning rates influence nestling development with consequences for their survival and fitness as adults, but provisioning behavior can be disrupted by predation risk. For an alpine population of Horned Lark (Eremophila alpestris) on Hudson Bay Mountain, British Columbia, we tested the effects of perceived predation risk on parental provisioning behavior. Using a repeated measures experimental design, we presented nests with decoys representing 3 levels of predation risk: (1) a scent-oriented predator (red fox; Vulpes vulpes), (2) a visually oriented predator (Common Raven; Corvus corax), and (3) a noncompetitive sympatric species (Savannah Sparrow; Passerculus sandwichensis) as a control. We found that elevated perceived predation risk decreased parental nest visitation rate by 65.6% compared to the control rate (mean 0.64 [SE 0.04] visits per 10 min), with no difference in response to predators that use visual (raven: 0.17 [0.03]) or olfactory (fox: 0.27 [0.04]) cues after controlling for zero inflation. Although background levels of provisioning behavior differed between sexes, we found no evidence for sex-specific responses to perceived predation risk. Horned Larks did not compensate for reduced visitation rates by increasing prey bill-load size, and thus an overall decrease in biomass delivery occurred during predator presentations. Females increased nest visitation rates immediately (30 min period) following fox decoy presentations, however, such that the net biomass delivery rate was comparable to control rates. This immediate compensatory behavior was not observed for females following raven treatments or for males. We showed that Horned Lark parents can assess and respond to increased perceived predation risk and provide evidence for compensatory provisioning behavior, which may indicate the potential to cope with habitats experiencing elevated mesopredator densities.

Animal species gain protection against visually oriented predators when they choose a suitable substrate that maximizes camouflaging. The choice of appropriate substrate may be particularly important during the brooding period when vulnerability of the parents and their progeny is high. The Common Potoo (Nyctibius griseus) is a well-camouflaged bird that blends nearly perfectly into a branch extension. Camouflage may be so effective for this species that perched individuals may wait until the last second before fleeing a potential predator. We compared the features of day perch substrates used by this bird during nesting and nonnesting occasions. We accessed 1,560 photos online and found that Common Potoo predominantly use natural tree substrates for nesting and resting (1,510 photos, 96.8%), except for a small percentage of individuals (50 photos, 3.2%) that choose seemingly risky artificial substrates (e.g., wires, traffic poles, and even plastic bottles) as resting sites. In addition, a random subsample of 150 photographs of individuals perched on trees revealed (1) prominently similar features of nesting perches chosen by adults during the nestling and not fully fledged stages of their offspring, and (2) a more flexible choice of tree substrate features by adults during the nonnesting period. We hypothesized that during the nesting period, adult behavior is to use perches that increase crypsis (i.e., with minimal probability of detection by visually oriented predators). Adults, in the absence of nestlings and not fully fledged juveniles, may be more flexible in choosing resting substrates, taking advantage of the masquerade effect. Received 5 October 2016. Accepted 11 June 2017.

The appearance of wood substrates is likely relevant to bird species with life histories that require regular interactions with wood for food and shelter. Woodpeckers detect decayed wood for cavity placement or foraging, and some species may be capable of detecting trees decayed by specific fungi; however, a mechanism allowing for such specificity remains unidentified. We hypothesized that decay fungi associated with woodpecker cavity sites alter the substrate reflectance in a species-specific manner that is visually discriminable by woodpeckers. We grew 10 species of wood decay fungi from pure cultures on sterile wood substrates of 3 tree species. We then measured the relative reflectance spectra of decayed and control wood wafers and compared them using the receptor noise-limited (RNL) color discrimination model. The RNL model has been used in studies of feather coloration, egg shells, flowers, and fruit to model how the colors of objects appear to birds. Our analyses indicated 6 of 10 decayed substrate/control comparisons were above the threshold of discrimination (i.e., indicating differences discriminable by avian viewers), and 12 of 13 decayed substrate comparisons were also above threshold for a hypothetical woodpecker. We conclude that woodpeckers should be capable of visually detecting decayed wood on trees where bark is absent, and they should also be able to detect visually species-specific differences in wood substrates decayed by fungi used in this study. Our results provide evidence for a visual mechanism by which woodpeckers could identify and select substrates decayed by specific fungi, which has implications for understanding ecologically important woodpecker–fungus interactions.

Seasonally dry tropical forest is the least known and most threatened ecosystem in the Neotropics. In December 2009, we surveyed 3 tropical dry forest remnants in the arid Cúcuta valley, northeast Colombia. We recorded 140 of the 171 maximum species expected for the study area. Another 20 species were observed outside the inventory, totaling 160 species for the whole region. Results of the similarity analysis showed that the Cúcuta valley avifauna is biogeographically more related to the arid inter-Andean river valleys than to the Caribbean plains of Colombia and the Caribbean lowlands of northern Venezuela. This pattern of biogeographical affinities of dry forest bird communities in northwestern South America seems to be explained by the effect of geographic distance rather than environmental differences shaping species composition (β-diversity) and phylogenetic relatedness (phyloβ-diversity) across space. Our results highlight the uniqueness and need to protect the topical dry forest remnants of the Cúcuta valley.

We assessed differences in diet composition between Imperial Cormorants (Phalacrocorax atriceps) breeding at Isla Arce and Isla Vernaci Este, Golfo San Jorge, Argentina. Both colonies are located within the Patagonia Austral marine park, and commercial trawl fisheries operate in adjacent waters, thus knowledge of their food requirement is fundamental to assess potential conflicts and monitor interactions. We obtained stomach samples from 63 adult Imperial Cormorants during the chick-rearing period in 2014: 32 at Isla Arce and 31 at Isla Vernaci Este. We recorded 27 and 30 prey taxa in stomach samples at Isla Arce and Isla Vernaci Este, respectively, and at least 21 were common to both islands. Significant differences in diet composition in terms of importance by mass were found between young and old chick stages at Isla Arce but not at Isla Vernaci Este. Rock cod (Patagonotothen spp.) were dominant at Isla Vernaci Este during both chick stages (75.7% and 86.5%, respectively). At Isla Arce, rock cod, Argentine anchovy (Engraulis anchoita), and Argentine hake (Merluccius hubbsi) contributed similarly to their diet (26–33%) during the young chick stage, whereas Argentine anchovy dominated during the old chick stage (76.6%). Diet composition in terms of importance by mass was significantly different between colonies. Imperial Cormorant consumed benthic, demersal, and pelagic prey, confirming plasticity in feeding habits, but their contribution differed depending on the site and chick stage. Our results suggest that diet assessments and monitoring the potential interaction between Imperial Cormorant and fisheries should not be based on information from a single breeding stage or location, but requires the analysis of diet composition throughout the breeding cycle with a representative sampling of the 17 colonies within the marine park.

The island of Makira in the eastern Solomon Islands is a globally significant priority for bird conservation and, like other islands in Melanesia, its avifauna plays an important role in understanding patterns of biogeography and speciation. Large portions of the island have rarely been visited by ornithologists, however, and published natural history information is limited for many species. We conducted field surveys, interviews, and camera trapping on Makira from October 2015 to February 2016, including the first ornithological surveys in southern Makira. We identify minor differences between the bird communities in the southern and northern parts of the island and report on noteworthy natural history observations, including nest descriptions for Yellow-legged Pigeon (Columba pallidiceps) and Shade Warbler (Horornis parens). We did not detect 3 endangered terrestrial species (Makira Woodhen [Gallinula silvestris], Thick-billed Ground-Dove [Gallicolumba salamonis], and White-bibbed Ground-Dove [Gallicolumba jobiensis]), and all 3 are probably extinct on Makira. High numbers of invasive species are present throughout Makira's forests, in particular rats (Rattus spp.), which were found at all our survey sites and accounted for nearly 34% of camera trap images, and cats (Felis catus), which were recorded at all sites that received >75 camera-days of survey effort. The widespread presence of invasive predators in remote and unlogged forests helps explain the disappearance of native species from the island. Controlling unregulated logging and protecting the remaining lowland forest in southern Makira is now the most important priority for biodiversity conservation on the island. In addition to our own observations, we review findings from other ornithological fieldwork on Makira and provide a comprehensive list of 114 bird species recorded on the island.

The Common Green Magpie (Cissa chinensis) is a nest predator in tropical evergreen forests of Indomalaya and is likely impacting the reproductive success of other birds nesting in areas where it occurs. We studied the Common Green Magpie's nest-site selection in northeastern Thailand between March and July 2015. We actively searched for Common Green Magpie nests, recorded and compared vegetation variables such as vegetation cover and stem density at 32 nest sites with 64 randomly selected non-nest sites, and modeled nest-site selection using generalized linear models. The results indicated that vegetation cover (at heights 1–3 m, >3–5 m, and >5–7 m) and stem density (at heights >3–5 m and >5–7 m) were significantly greater at nest sites than at random sites. The GLM analysis indicated that vegetation cover at >5–7 m and stem density at >7 m were the most important vegetation variables influencing nest site selection by these magpies. Choice of sites with greater vegetation cover and stem density may be an anti-predator strategy that reduces nest predation risks and protects eggs and nestlings from harsh weather. Our findings add to our understanding of the ecology of a major nest predator in Asian tropical forests.

Laying interruptions, or even a several-day hiatus during egg laying, have been documented in response to a variety of environmental and internal factors. These interruptions alter the laying schedule of the affected female and have been documented to impact final clutch size in some, but not all, species. The Yellow Warbler (Setophaga petechia), a migratory songbird species, is a determinate layer that typically lays one egg every 24 h until clutches are complete—usually 4 or 5 eggs at Delta Marsh, Manitoba. Nesting observations were recorded from 1974 to 2010 at 961 nests in which laying was occasionally interrupted. Laying interruptions influenced the final clutch size in one of 2 ways. (1) Complete clutches were still laid after a possible delay in ovulation past the ‘optimal period.' Five-egg clutches in nests that experienced a laying interruption provide support for this scenario because 5 eggs is accepted as the largest clutch size generally recorded in this population. (2) Warblers interrupted laying for at least a day but did not lay another egg to compensate for the lost days during the interruption, resulting in smaller clutches on average (i.e., more 3- and 4-egg clutches), possibly because females were incapable of laying due to environmentally or nutrient deficiency induced atresia. The increase in 3-egg clutches and timing of interruptions in the laying cycle support the latter scenario. Date in the breeding season, order in the laying sequence, and, to some extent, higher temperatures preceding clutch initiation promoted the occurrence of laying interruptions. Laying interruptions significantly influenced final clutch sizes, which in turn could affect the reproductive output of the population.

Courtship and copulation constitute crucial elements of avian reproduction and fitness. Despite the potential impact of environmental perturbations and long-term climate change on avian reproduction, few studies provide quantitative information on courtship and copulation behaviors and their responses to proximate environmental factors. We provide the first quantitative description of courtship and copulation behavior in Glaucous-winged Gulls (Larus glaucescens), an important indicator species of marine environmental quality in North America's Pacific Northwest. Male and female Glaucous-winged Gulls exhibited similar frequencies of most pre- and post-mount behaviors, which closely resemble those used by other larids. Mounts were more frequent than expected during the pre-egg-laying and egg-laying stages of the breeding season and less frequent than expected during the incubation stage. In 2008, numbers of successful copulations vs. unsuccessful copulations, numbers of cloacal contacts per successful copulation, and copulation duration did not differ by reproductive stage. In 2012, copulation duration increased with day of the year and decreased with wind speed, and the number of cloacal contacts per copulation decreased with wind speed. The odds of paired head toss increased with tide height and decreased with solar elevation. The odds of female courtship beg increased with the number of days from its peak occurrence, and also with solar elevation, tide height, and Bald Eagle (Haliaeetus leucocephalus) disturbances. Mount interval, the time from the start of one mount in the study area to that of another, was positively related to time of day, barometric pressure, and solar elevation but was negatively related to solar radiation and colony occupancy. Both the temporal and spatial occurrence of copulation were socially facilitated by the behavior of neighboring birds in the colony. Our results suggest that changes in environmental variables due to climate change could affect reproductive behaviors and reproductive success in this species.

Although plumage displays often reliably signal individual condition and age, how these sexually selected traits vary with geographic region is not well understood. Golden-winged Warbler (Vermivora chrysoptera) populations are fragmented and declining precipitously in the Appalachian Mountains. Limited research suggests that Golden-winged Warbler facial plumage ornaments may be under sexual selection; black throat (melanin-based) coloration is associated with mate acquisition while yellow crown (carotenoid-based) coloration is associated with aggression and habitat quality. We tested whether multiple plumage traits (crown, throat, and tail coloration) (1) varied across the Appalachian breeding range, (2) varied with age class or body condition, and (3) covaried with each other and whether the covariance differed with geographic region. We found that crown and throat coloration followed a latitudinal gradient, with the more southern birds showing lower ornamentation. Moreover, after-second-year birds had tails with a greater extent of white than second-year, suggesting tail color may reliably signal age that conspecifics could assess. Males with more-ornamented crown color had more-ornamented throat coloration, suggesting that this species demonstrates some potential for both redundant (facial coloration) and independent (tail white) signaling. We found no evidence, however, that covariation between traits differed across the breeding range or that the plumage traits varied with body condition. Additional research investigating the signaling function of multiple plumage ornaments in Golden-winged Warblers across their breeding range could shed light on habitat preferences and communication. Received 28 October 2016. Accepted 4 January 2018.

White terns (Gygis alba) are common on many islands in the tropical and subtropical Pacific, Atlantic, and Indian oceans, but in the southeastern Hawaiian Islands they are found only on Oahu, where they are listed as threatened by the State of Hawaii. In 2016, we censused the White Tern population on Oahu, mapped their distribution, and investigated their breeding biology. The total White Tern population on Oahu was 2,308 birds, including 1,408 breeders and ∼900 nonbreeders. The number of White Terns on Oahu has increased 282% since the previous census in 2002, for an average annual population growth rate of 7.7%. We observed White Terns only in urban and suburban areas of Honolulu and not in other parts of the island. Breeding occurred year-round, with 2 peaks in egg-laying in March and October. Hatching success was 69%, fledging success was 83%, and overall breeding success was 57%. Pairs made an average of 1.75 (SE 0.09) breeding attempts per year and produced an average of 1.08 (0.09) offspring per year (range 0–3). Terns used >58 tree species for breeding and roosting, most of which were large (>45 cm diameter). Average height in trees of breeding attempts was 9.1 (0.2) m. White Terns are thriving in urban Honolulu and are not seriously affected by numerous potential sources of human disturbance or predation from nonnative mammals, but some efforts will help to ensure their status remains secure. Received 7 July 2017. Accepted 6 January 2018.

We monitored 25 Golden Eagles in Montana, USA, from 2011 to 2015 over 3,601 days using tail-mounted satellite transmitters. Using the best available direct observation and circumstantial evidence, we surmise that only a single eagle (adult female floater) died during monitoring, resulting in a daily survival estimate of 0.9997 (SE = 0.0003) and an annual survival estimate of 0.905 (SE = 0.0907) for a mixture of adult and younger, resident and migrant, breeder and nonbreeder eagles of both genders living in relatively undisturbed regions of the western United States. Under this scenario, adult daily survival averaged 0.9996 (SE = 0.0004) and adult annual survival averaged 0.858 (SE = 0.132).

Although feeders provide supplementary food to wild birds, they can be a site of disease transmission. Periodic cleaning of bird feeders is recommended to prevent disease transmission, but little is known about which cleaning methods are most effective. We determined the effectiveness of 3 cleaning methods (scrubbing with soap and water, bleach soak, and scrubbing with soap and water followed by a bleach soak) in removing Salmonella from feeders with debris from normal field use and without debris. Feeders were inoculated with Salmonella enterica in the lab and then swabbed before and after cleaning to determine the percent reduction of Salmonella colony forming units (CFU/mL). All cleaning methods effectively reduced levels of Salmonella on feeders without debris, but the presence of debris significantly lowered the percent log reduction of Salmonella CFU/mL on feeders. The bleach soak and the scrubbing with soap and water plus bleach soak methods had a significantly higher percent reduction in Salmonella CFU/mL than the scrubbing with soap and water method overall. A significant interaction between debris and cleaning method was noted, however, indicating that the presence of debris greatly lowered the percent reduction of Salmonella CFU/mL on feeders cleaned with the scrubbing with soap and water method compared to other methods. Overall, we recommend either scrubbing with soap and water or a bleach soak to clean feeders with minimal debris, but suggest a combination of these 2 cleaning methods if feeders have heavy debris or if diseased birds are known to be in the area. Received 20 September 2016. Accepted 17 January 2017.

Catching ground feeding birds has typically been accomplished through small, walk-in funnel-style traps. This approach is limited because it requires a bird to find its way into the trap, is biased toward less wary birds, and does not allow targeted trapping of individual birds. As part of a large study on Band-tailed Pigeons (Patagioenas fasciata) in New Mexico, we needed a trapping method that would allow more control over the number of birds we could trap at one time, when a trap was deployed, and target trapping of specific individuals. We adopted a relatively novel trapping technique used primarily for shorebirds, whoosh nets, to trap Band-tailed Pigeons at 3 different sites where birds were being fed by local landowners. During 2013–2015, whoosh nets were used to trap 702 Band-tailed Pigeons at 3 different locations in New Mexico. We captured 12.54 ± 8.19 pigeons per shot over 56 capture events across 3 locations (range: 2–39). Some superficial injuries occurred using this technique and typically involved damage to the primary and secondary wing coverts. In 2013, 24% of captured birds had an injury of this nature, but after modifying the net speed, injury rates in 2014 and 2015 dropped to 8% and 7%, respectively. Recaptured previously injured birds showed new feather growth within 2 weeks and showed no signs of injury after 4 weeks. Whoosh nets proved to be a highly effective solution for trapping large numbers of pigeons at baited sites. These systems are easily transported, quickly deployed, and easily adapted to a variety of site conditions. Received 5 May 2016. Accepted 6 March 2017.

DNA sampling is an essential prerequisite for conducting population genetic studies. For many years, blood sampling has been the preferred method for obtaining DNA in birds because of their nucleated red blood cells. Nonetheless, use of buccal swabs has been gaining favor because they are less invasive yet still yield adequate amounts of DNA for amplifying mitochondrial and nuclear markers; however, buccal swab protocols often include steps (e.g., extended air-drying and storage under frozen conditions) not easily adapted to field settings. Furthermore, commercial extraction kits and swabs for buccal sampling can be expensive for large population studies. We therefore developed an efficient, cost-effective, and field-friendly protocol for sampling wild birds after comparing DNA yield among 3 inexpensive buccal swab types (2 with foam tips and 1 with a cotton tip). Extraction and amplification success was high (100% and 97.2% respectively) using inexpensive generic swabs. We found foam-tipped swabs provided higher DNA yields than cotton-tipped swabs. We further determined that omitting a drying step and storing swabs in Longmire buffer increased efficiency in the field while still yielding sufficient amounts of DNA for detailed population genetic studies using mitochondrial and nuclear markers. This new field protocol allows time- and cost-effective DNA sampling of juveniles or small-bodied birds for which drawing blood may cause excessive stress to birds and technicians alike. Received 28 June 2016. Accepted 4 January 2017.

The first case of overlapping broods for the Red-tailed Comet (Sappho sparganurus) is documented. While feeding 2 chicks from a first brood, a female simultaneously began to build a second nest and successfully raised 2 young in each. The length of overlap of the 2 nests was estimated at 17 d. This is the first record of partial nest overlap for a hummingbird species in a temperate area in the Southern Hemisphere. In addition, these observations extend the altitudinal limit of this species 260 m below the previously lower boundary, which was for the nonbreeding season. Received 23 August. Accepted 6 March 2017.

The existence of a dark morph in adult Long-tailed Jaeger (Stercorarius longicaudus) is still unclear and debated. For this species, dark plumages occur in juveniles and immatures, but no dark morph adults have yet been unequivocally confirmed. Ambiguous reports of presumed dark morph adults and lack of information on molt progression of immatures generate confusion regarding this issue. Here we describe observations conducted in the Canadian Arctic (Bylot Island) and show that Long-tailed Jaegers can apparently exhibit dark morph adult-like plumage (i.e., individuals showing some obvious criteria associated with definitive alternate ‘adult breeding' plumage). Careful examination of those sightings, however, also revealed immature characteristics, indicating the high variability of the first prealternate molt in this species. Well-documented observations of rare plumages like the one reported in this study are needed to elucidate molting strategies and polymorphism in Long-tailed Jaeger. Received 4 October 2016. Accepted 3 June 2017.

Brood reduction by parents via infanticide is considered rare in passerine birds; however, this behavior may be underreported because of the difficulties observing behaviors at the nest and because researchers tend to attribute partial nestling loss to other causes. Here, we report a confirmed incidence of parental infanticide by Dickcissels (Spiza americana). While video-recording parental behavior, we documented a 4-day-old nestling being removed by a female Dickcissel. This bird was also observed brooding and feeding, so this event was likely a parental infanticide. We subsequently examined monitoring data from 162 hatched Dickcissel nests across 2 breeding seasons to identify instances of unexplained partial nestling loss, which could potentially be attributable to infanticide. Our data indicate that 9.1–12.7% of hatched nests experienced these events. Infanticide by genetic parents could (1) benefit survival of remaining brood mates by reducing food requirements, disease, or predation risk; (2) represent responses to cuckoldry or intraspecific brood parasitism; (3) represent cases of mistaken chick identity; or (4) be triggered by unusual stressors. We recommend that ecologists monitoring bird nests consider infanticide as a possible explanation for partial nestling loss. Received 3 November 2016. Accepted 27 November 2017.