We report on the first global census of the Adélie Penguin (Pygoscelis adeliae), achieved using a combination of ground counts and satellite imagery, and find a breeding population 53% larger (3.79 million breeding pairs) than the last estimate in 1993. We provide the first abundance estimates for 41 previously unsurveyed colonies, which collectively contain 420,000 breeding pairs, and report on 17 previously unknown colonies, 11 of which may be recent colonizations. These recent colonizations represent ∼5% of the increase in known breeding population and provide insight into the ability of these highly philopatric seabirds to colonize new breeding territories. Additionally, we report on 13 colonies not found in the survey, including 8 that we conclude have gone extinct. We find that Adélie Penguin declines on the Antarctic Peninsula are more than offset by increases in East Antarctica. Our global population assessment provides a robust baseline for understanding future changes in abundance and distribution. These results are a critically needed contribution to ongoing negotiations regarding the design and implementation of Marine Protected Areas for the Southern Ocean.

Several species of avian brood parasites have evolved egg mimicry, which can interfere with host egg rejection. Parasitic egg mimicry may select for decreased intraclutch variation in host egg appearance to facilitate the recognition and rejection of parasitic eggs. This hypothesis has received scant attention in hosts of the Brown-headed Cowbird (Molothrus ater) because the cowbird apparently has not evolved mimetic eggs. Nonetheless, hosts with eggs similar in appearance to cowbird eggs should minimize intraclutch variation to increase the likelihood of detecting parasitism. By contrast, there may be minimal selection pressure to reduce intraclutch variation in hosts with eggs that are divergent from cowbird eggs. Using reflectance spectrometry, we compared the intraclutch variation between accepters and rejecters of 2 groups of host species: those with eggs similar in appearance to cowbird eggs (white maculate eggs) and those with eggs that clearly diverge in appearance from cowbird eggs (blue eggs). We predicted that rejecters with white maculate eggs should have lower intraclutch variation than accepters, whereas accepters and rejecters with blue eggs should have similar amounts of intraclutch variation. The intraclutch variation between accepters and rejecters with blue eggs did not differ, which matched our predictions. However, rejecters with white maculate eggs did not consistently have lower intraclutch variation than accepters; thus, our hypothesis was not supported for this group. A more comprehensive study, focused on cowbird hosts nesting in grassland and edge habitats, is warranted to determine whether a pattern between intraclutch variation and egg rejection exists among hosts with white maculate eggs.

Imperfect detection during animal surveys biases estimates of abundance and can lead to improper conclusions regarding distribution and population trends. Farnsworth et al. (2005) developed a combined distance-sampling and time-removal model for point-transect surveys that addresses both availability (the probability that an animal is available for detection; e.g., that a bird sings) and perceptibility (the probability that an observer detects an animal, given that it is available for detection). We developed a hierarchical extension of the combined model that provides an integrated analysis framework for a collection of survey points at which both distance from the observer and time of initial detection are recorded. Implemented in a Bayesian framework, this extension facilitates evaluating covariates on abundance and detection probability, incorporating excess zero counts (i.e. zero-inflation), accounting for spatial autocorrelation, and estimating population density. Species-specific characteristics, such as behavioral displays and territorial dispersion, may lead to different patterns of availability and perceptibility, which may, in turn, influence the performance of such hierarchical models. Therefore, we first test our proposed model using simulated data under different scenarios of availability and perceptibility. We then illustrate its performance with empirical point-transect data for a songbird that consistently produces loud, frequent, primarily auditory signals, the Golden-crowned Sparrow (Zonotrichia atricapilla); and for 2 ptarmigan species (Lagopus spp.) that produce more intermittent, subtle, and primarily visual cues. Data were collected by multiple observers along point transects across a broad landscape in southwest Alaska, so we evaluated point-level covariates on perceptibility (observer and habitat), availability (date within season and time of day), and abundance (habitat, elevation, and slope), and included a nested point-within-transect and park-level effect. Our results suggest that this model can provide insight into the detection process during avian surveys and reduce bias in estimates of relative abundance but is best applied to surveys of species with greater availability (e.g., breeding songbirds).

Small-bodied birds engaging in incubation by a single sex experience a tradeoff between incubating to create a buffered thermal environment for their eggs and foraging to meet their own energetic requirements. This tradeoff is intensified in alpine environments, which are characterized by cold and variable conditions. We monitored the incubation rhythms of alpine Horned Larks (Eremophila alpestris) in British Columbia, Canada, across different annual thermal regimes (2005: moderate; 2006: warm; 2010: cold overnight; 2011: cold during the day). In this species, females alone incubated and left their nests to forage at dawn, following 7 hr of nighttime incubation in near-freezing conditions. However, with early morning ambient temperatures still <5°C, this placed embryos at high risk of chilling during incubation recesses. Focusing on behavioral decisions made by females at dawn (06:00–08:00 hours), we examined relationships between incubation rhythms and ambient temperature among years for evidence of variable responses to temperature. In all years, females spent more time off the nest at dawn in warmer temperatures, but in 2010, which was colder overnight, the slope of the line relating attentiveness to ambient temperature was steeper, indicating that females left their nests at colder temperatures compared with other years. In 2010 females also took shorter recesses at cold temperatures. Hatching success remained high in 2010 relative to warm or moderate years; however, overwinter survival of females declined to 48% from 2010 to 2011 compared with 72% in earlier years. When faced with exceptional thermal constraints, alpine Horned Larks made behavioral adjustments to their incubation rhythms and were able to maintain fecundity. However, potential survival costs to females implies a shift in balance of the parent–offspring tradeoff, revealing limits to coping mechanisms of alpine-breeding Horned Larks.

The average number of eggs in a clutch and the size of those eggs play a role in individual fitness. We explored sources of variation in egg allocations of female Greater Sage-Grouse (Centrocercus urophasianus) in the American Great Basin over a 10-yr period, as well as range-wide variation in clutch size, using our data and other published values. We tested for environmental and individual effects on clutch size (n = 390) and egg volume (n = 2,486) in a mixed-modeling framework, with random-effect terms that described variation among individual females (i.e. heterogeneity) and allowed us to calculate repeatability for clutch and egg size. The strongest influence on clutch size was the timing of nest initiation, which varied by as much as 67 days within years and showed a negative linear relationship with clutch size. Once this pervasive effect was accounted for, we also found positive effects of annual precipitation and nest-site elevation. In wetter years and at more productive high-elevation sites, females laid larger clutches, which suggests that some degree of large-scale resource availability affects clutch size. The fixed effects in our models explained ∼34% of the total variance in clutch size, and individual random effects explained an additional 15% (repeatability = 0.15). In contrast to clutch size, little measurable variation in egg volume could be attributed to the fixed effects we considered, and ∼60% of the variance in egg volume was associated with random effects (repeatability = 0.59). Prenesting female body condition influenced clutch size, and this effect was most pronounced for replacement clutches. We found repeatability for clutch and egg size to be within the range of published estimates for other avian taxa. Across studies, mean clutch size increased with latitude, demonstrating that Greater Sage-Grouse follow geographic patterns in clutch size that are consistent with other avian taxa.

Of the 13 taxa composing the Mallard complex, 4 occur in North America: the sexually monochromatic American Black Duck (A. rubripes), Mexican Duck (A. [platyrhynchos] diazi), and Mottled Duck (A. fulvigula), and the dichromatic Mallard (Anas platyrhynchos). Although morphologically distinct, inferring the evolutionary relationships of this group is confounded by extensive genic sharing due to incomplete lineage sorting and ongoing hybridization. The objective of this study was to examine the underlying cause (i.e. incomplete lineage sorting vs. contemporary gene flow) of phylogenetic uncertainty. Whereas most taxa were fairly structured at mitochondrial DNA, a “starburst” pattern of divergence consistent with a rapid radiation was recovered with 17 nuclear introns. Furthermore, nuclear-based divergence estimates and tests of population structure recovered Florida and West Gulf Coast Mottled Ducks as well-differentiated and genetically diagnosable from each other and the remaining taxa, whereas Mallards, American Black Ducks, and Mexican Ducks were indistinguishable. In general, neither population structure analyses nor coalescent-based gene flow estimates conclusively identified the presence of hybrids or significant gene flow, suggesting that genetic similarity within the group is largely influenced by incomplete lineage sorting. However, we also cannot reject potentially high levels of gene flow. Moreover, inconsistent relationships among species trees indicated that phylogenetic results were sensitive to which individuals were included. Taxa within the New World group are phenotypically distinguishable, yet genetically similar and seemingly lack the apparent reproductive isolation that is consistent with early stages of (incomplete) speciation. Future work should focus on genomic regions under selection to better understand the stage of speciation among the various incipient forms.

Nest placement presumably reflects selection for secure sites to minimize failure. Most tests of this hypothesis, however, have failed to support it. We used artificial nests (ARTs) to experimentally evaluate nest-site-choice behavior by an open-cup–nesting bird, the Eastern Kingbird (Tyrannus tyrannus). In 2010 and 2011, we placed ARTs in trees in the riparian zone at Malheur National Wildlife Refuge, Oregon, USA, to test whether (1) characteristics describing the physical location in trees of used and unused ARTs differed, (2) used ART sites more closely resembled naturally chosen sites, (3) successful natural nests (NATs) and successful ARTs were similarly located along the major axis describing nest placement, and (4) unused ARTs resembled failed NATs. Used and unused ART sites differed, but unused ART sites were more similar to NAT sites. The latter unexpected result occurred because (1) unused ARTs were located at sites between more heavily used higher and lower locations and (2) most kingbirds nesting at lower locations used ARTs instead of building their own nest. In both ARTs and NATs, differences between successful and failed nests exhibited the same pattern for most nest-site variables, and the major gradient describing nest location was the same; successful nests tended to be placed on more vertically oriented branches that were placed closer to the top of the tree. Kingbird nest placement was thus selective. However, extensive overlap in the locations in trees of failed NATs and both successful and unused ARTs suggests that other factors, such as macrohabitat characteristics or prior experience of individual birds with particular nest sites, may have influenced success and/or decisions to use or reject nests in particular locations. Thus, consideration of phenomena beyond the nest site itself may be required to fully understand the process of nest-site choice in birds.

Obligate brood parasites, which typically lack reliable interactions with conspecifics early in life, acquire species recognition cues by mechanisms other than imprinting on parents and siblings. The African indigobirds (Vidua spp.) are exceptional among brood parasites in that learning and mimicry of host vocalizations play an integral role in the social behavior of the parasites. Male indigobirds have impressive vocal repertoires featuring chatter calls, host mimicry, and complex non-mimicry songs. While chatter calls are similar, sympatric indigobirds are distinguished both by their mimicry of different hosts and by unique repertoires of non-mimicry songs. A previous playback experiment showed that male indigobirds respond differentially to natural singing (i.e. playbacks including host mimicry, chatter, and complex non-mimicry) of sympatric conspecifics and heterospecifics, but the relative role of host mimicry and complex non-mimicry in species recognition remains unknown. We addressed this question in a playback experiment that tested the response of focal males to 3 treatments: sympatric conspecific, allopatric conspecific (same host mimicry combined with unfamiliar complex non-mimicry songs), and sympatric heterospecific (different host mimicry and different, but familiar, complex non-mimicry). Three behavioral responses (number of hops, latency of response, and number of chatter calls) were similar in the 2 conspecific treatments but differed in comparison with the heterospecific treatment. Our study provides evidence that host mimicry is an important cue in species recognition among territorial male indigobirds and suggests that it may contribute to species cohesion when juveniles or adults disperse beyond the boundaries of their local dialect neighborhood. This study enhances our understanding of avian recognition systems by showing that cues obtained through heterospecific imprinting can be important for species recognition in brood parasitic birds.

Understanding how distributions of species change through time allows evaluation of hypotheses about factors shaping biogeographic patterns and evolutionary trajectories of genetic lineages. Ideally, such studies would assess whether population genetic processes are associated with geographic distribution shifts, loss or gain of distributional area through time, or fragmentation of distributional areas, information that can now be derived via ecological niche modeling. We examined the distributional changes through time in lineages and populations of Brown Creeper (Certhia americana), a widespread North American bird, to test biogeographic and population genetic hypotheses. In two populations with genetic support for population bottlenecks, Monterey County in California and the Sierra Madre Oriental in Mexico, ecological niche models indicated range contractions and increased fragmentation since the Last Glacial Maximum (LGM). Projections of niche models to the future suggested continuation of range contractions and fragmentation. Of the 3 major allopatric lineages of Brown Creeper (eastern North America, western North America, and southern North America and Central America), the most stable through time was the southern lineage, which corresponds with increased genetic diversity. The potential geographic distribution of the western lineage has remained stable in size but not location since the LGM, corresponding with a genetic signal of isolation by distance. The eastern lineage experienced range contractions during the LGM, likely resulting in the contemporary lack of genetic structure within the lineage. Finally, there is limited evidence of potential range overlap during the LGM between the western lineage and the other 2 lineages, although the overlap is limited to the Arizona sky islands between the west and south lineages. These results suggest that ecological niche modeling and population genetic data may be used as mutual predictors when investigating phylogeographic patterns and processes.

Brood enlargement experiments have been conducted in several species of birds to investigate how parents of both sexes adjust their investment in the current breeding attempt. We studied parental feeding effort in the Northern Flicker (Colaptes auratus), a species with partially reversed sex roles where males invest more in parental care than females and in which there is facultative polyandry and no extra-pair young. By experimentally manipulating brood sizes to be either larger or smaller by about 40%, we tested the flexibility of provisioning responses by each sex and whether the upper limit to provisioning corresponded to the maximum clutch size in the population. Both male and female parents increased feeding rates to enlarged broods, but per-nestling provisioning declined so that they fledged lighter nestlings with shorter wings. Mortality in reduced broods was lower than in control broods, but there was no difference in the incidence of mortality between control and enlarged broods. Parents with enlarged broods raised lighter fledglings than control parents with the same brood size suggesting clutch size is individually optimized. We conclude that, although flickers were able to raise extra offspring, brood size may be individually optimized if the smaller mass and wing length of offspring lead to lower recruitment.

The evolution of egg mimicry by parasites and the recognition of foreign eggs by hosts are important components of the coevolutionary arms race between brood parasites and their hosts, which is one of the most behaviorally complex of all host–parasite interactions. To examine cues used by the Yellow Warbler (Setophaga petechia), a non-ejecter that buries or deserts eggs laid by parasitic Brown-headed Cowbirds (Molothrus ater), we added model eggs of different sizes and colors to nests. We also reviewed the literature to investigate the effects of model egg surface color (background and maculation) and size on the response of hosts that eject. We predicted that size would be more important for Yellow Warblers as they likely use tactile cues to bury or desert parasitized clutches and color cannot be assessed tactilely. In Yellow Warblers, rejection frequency increased as size and color diverged more from real warbler eggs. Egg size was not generally used as a criterion for egg rejection, however, across different species that eject parasitic eggs. Color was the only model egg parameter, out of color and size, that significantly affected rejection in these ejecter hosts. Tactile cues are therefore not used by ejecters but are more important in a host that uses methods of rejection that do not require egg discrimination, such as burial and desertion. Of metrics that took into account the ultraviolet range, achromatic Just Noticeable Differences (brightness) in Yellow Warblers better predicted rejection of model eggs based on color than chromatic Just Noticeable Differences (hue). The high costs of burial and desertion may have led to multiple (size and color) egg discrimination abilities in the Yellow Warbler.

Seabirds forage in a highly dynamic environment and prey on fish schools that are patchily distributed. Colonially breeding seabirds regularly commute back and forth from their colony to foraging areas and need to acquire information on the location of food before and/or during each foraging trip. The use of conspecifics as cues to locate prey has long been debated, and although the hypothesis was backed up by modeling studies, observations have been contradictory. We deployed GPS devices coupled with micro video cameras on Cape Gannets to observe the social context of foraging seabirds and the influence of conspecifics on the movement of individuals. The Cape Gannets reached their first patch using a succession of flights interrupted by stops on the water, during which the birds were mainly preening. During flight, the birds reacted to conspecifics by changing direction, either flying in the opposite direction of conspecifics that were flying toward the colony or following conspecifics outward. The time to reach the first patch was significantly reduced (by half) when the birds reacted to conspecifics in these different ways, compared with the birds that did not react. The use of conspecifics flying toward the colony to find food is consistent with the hypothesis that colonies can act as a focal place for information transfer, with foragers updating their flying direction when they detect conspecifics flying toward the colony. The fine-scale reaction of seabirds toward each other at sea, and the associated improved foraging efficiency, as well as the division of trips into a succession of flights, constitute elements that indicate the existence and the use of a structured network among foraging Cape Gannets.

Brood-parasitic cowbirds are hypothesized to search for and locate host nests within a relatively constant area, as this is presumed to facilitate the monitoring of nests over time and the synchronization of parasitism with host laying. We tested this hypothesis in Shiny Cowbirds (Molothrus bonariensis) and Screaming Cowbirds (M. rufoaxillaris), two cowbird species that differ in host specificity and, apparently, in social mating system, by radio-tracking females and males for 3–6 consecutive days and determining individual daily morning ranges and cumulative morning ranges. In Shiny Cowbirds, the mean size of morning daily ranges and cumulative morning ranges was larger for males than for females, but we did not find a difference between the sexes in range size for Screaming Cowbirds. In both species, there was extensive overlap in the morning ranges of individual females between consecutive days, and the addition of new area to their ranges decreased over time. For both Shiny and Screaming cowbirds, morning ranges of conspecific females radio-tracked the same day overlapped, indicating lack of territoriality. Male and female Screaming Cowbirds that were trapped together were also spatially associated during radio-tracking, indicating social monogamy. Most radio-tracked Shiny and Screaming cowbirds used mainly one roost, relatively close to their morning ranges, which was maintained throughout the breeding season. Our results show that Shiny and Screaming cowbird females use relatively constant areas for nest searching and that Screaming Cowbirds are socially monogamous.

The alternative prey hypothesis (APH) suggests that the functional and numerical response of predators to fluctuating rodent populations may drive annual variation in predation pressure on other available prey such as bird eggs. Most studies that have provided evidence supporting the APH in arctic bird populations have been conducted in the eastern hemisphere, and considerably less evidence for APH has emerged from western hemisphere populations. We tested the hypothesis that predation pressure on shorebird nests would increase as lemming abundance decreases due to apparent competition between lemmings and shorebirds via their shared predators in the eastern Canadian High Arctic. Over a period of 5 years on Bylot Island, Nunavut, Canada, we found that lemming abundance had a significant negative effect on predation risk as measured by artificial nests. Survival probabilities of artificial nests were also negatively related to fox abundance but positively associated with the abundance of breeding avian predators, likely due to predator exclusion around avian predator nests. Models of daily nest survival for real nests also indicated that interannual variation in nest survival was best explained by lemming abundance. Combined results from both artificial and real nests indicate that fluctuations in lemming populations likely have an indirect effect on predation pressure on shorebird eggs in the Canadian High Arctic, although mechanisms explaining the observed relationship require further investigation.

The Rufous-tailed Tailorbird (Orthotomus sericeus)—a Sunda endemic—is divided into 3 morphologically based subspecies: one in western Sundaland (Malay Peninsula, Sumatra, and associated islands), one from the Natuna Islands in the South China Sea, and one on Borneo, Palawan, and smaller islands of the Sunda continental shelf east of Borneo. Previous study, however, suggested that these subspecies do not conform to molecular genetic subdivisions of the species. We reexamined the morphology and performed molecular phylogeographic and multi-locus coalescent analysis of two subspecies of Rufous-tailed Tailorbird comprising populations on the Malay Peninsula, Sumatra, Borneo, and Palawan. We found (1) little morphological difference among the two subspecies, (2) no substantial genetic differences between the Borneo and western Sunda populations, but (3) marked genetic divergence between the Palawan and other populations. We conclude that the Bornean and western Sunda populations interbred extensively during Quaternary glacio-eustatic land connections, whereas the Bornean and Palawan populations did not. Unlike the other Greater Sunda Islands, Palawan has not been attached by a land bridge to the rest of Sundaland for at least one million years, and its relative isolation has prevented extensive intermixing between Palawan's and other Sunda populations. Thus, the Palawan population appears to be on its own evolutionary trajectory. The ability to demonstrate extensive interbreeding among some Sunda island populations, but not others, illustrates the practicality of testing Gill's (2014) “null hypothesis” that morphologically distinct populations on different islands are different species unless a compelling argument can be made to the contrary. In this case, Rufous-tailed Tailorbird morphology provided little or misleading evidence of the extent of interbreeding, whereas modern genetic analysis provided a clear view.

An isolated population of tapaculos attributed to Scytalopus speluncae has been known from the mountains of southeastern Bahia state, Brazil, since the early 1990s, and a second isolated population was discovered in 1999. Morphological and bioacoustic analyses of 11 specimens and several tape recordings indicated that these populations represent a new species, in agreement with a previous molecular phylogenetic study. This species is unambiguously distinguished from its closest relatives by 4 suites of characters: (1) morphometrics–body proportions, (2) plumage color, (3) vocalizations, and (4) genetics. Using each of these character sets, separately or in combination, one can distinguish with 100% confidence the new species from its sister lineages. The new species is known from only 5 localities distributed in 2 distinct mountain ranges, 1 on the eastern slopes of the Planalto da Conquista, between the municipalities of Boa Nova and Iguaí, and another in the Serra das Lontras, ∼100 km to the southeast and only 37 km from the coast. The new species primarily inhabits undisturbed montane forest, from 660 to 1,140 m a.s.l. We estimated an area of occupancy of the species of only 5,885 ha and a density of 0.49 individuals ha⁻¹, resulting in a total estimated population of 2,883 individuals. Forest remnants are under severe pressure from clandestine timber extraction and outright deforestation. Under IUCN criteria, this new species should be classified as “Endangered.”

Sperm competition, whereby sperm from multiple males compete to fertilize an egg, selects for adaptations that increase fertilization success. Because fertilization success is related to sperm number, size, and quality, both interspecific and intraspecific variation in these traits are predicted to correlate with the level of sperm competition. Specifically, species and individuals that experience high sperm competition are predicted to produce more sperm per ejaculate, produce longer sperm, and exert higher quality control, resulting in reduced numbers of morphologically abnormal sperm and reduced size variation via selection for the most successful sperm phenotype. However, the causes of sperm morphological and size variation and its consequences for sperm competition remain poorly understood, especially within species. We quantified variation in sperm morphology, size, and number in the Lance-tailed Manakin (Chiroxiphia lanceolata), a Neotropical suboscine passerine with a cooperative lek mating system. Although alpha-status males sire almost all chicks, the numbers of sperm produced per ejaculate by betas, nonterritorial adults, and subadult males were similar to those produced by alphas. Sperm counts declined with age in alphas, which may explain the decreased siring success of older alphas. Most ejaculates contained both normal helical sperm and abnormal sperm with rounded heads. The proportion of morphologically normal sperm per ejaculate was unrelated to social status or age. The coefficients of variation in sperm component length (head, tail, and total) both between and within alpha males were comparable to variation reported in passerines with low sperm competition. Total sperm length was shorter than in the majority of avian species studied to date, and cloacal protuberance and relative testis size were small. These results indicate low sperm competition, despite evidence for multiple paternity, or that sperm number rather than sperm morphology may be a major postcopulatory mediator of male reproductive success in this species. This work represents the first thorough quantification of intraspecific sperm variability in a suboscine passerine.

Optimal development of avian embryos occurs within a narrow range of incubation temperatures. Most parents that physically incubate their eggs through direct contact are challenged to balance their time on the nest with taking foraging recesses to satisfy their energetic requirements. To explore the costs and investment strategies of incubating female Wood Ducks (Aix sponsa), we manipulated the microclimate of nests by reducing down insulation from the typical 4.0 g to 0.5 g. Cooling rates of clutches during morning recesses increased when down insulation was reduced, especially at low ambient temperatures. Females with reduced down responded to increased cooling rates by shortening morning recesses and increasing daily incubation constancy, and these behavioral changes were independent of their body mass at the start of incubation. Females in both treatment groups responded similarly to changes in ambient temperature and spent less time incubating as ambient temperatures increased. Clutch temperatures at the end of morning recesses were similar for females with reduced and normal insulation. Average clutch temperatures for the full incubation period did not differ between treatments, and, correspondingly, there were no differences in length of the incubation period, hatching success, or duckling phenotype. Our results show that female Wood Ducks were sensitive to changes in both clutch temperature and ambient temperature and that they modified their time on the nest to provide developing eggs with an optimal thermal environment without negatively affecting their body mass at the end of incubation. Further examination of the limits of behavioral plasticity in incubating birds will be essential, particularly in light of future challenges presented by climate change.

How animals use space has fundamental behavioral and ecological implications. Utilization distributions are among the most common methods for quantifying space use and have advanced our knowledge of animal ecology in a variety of ways. However, until recently, they were limited to 2 spatial dimensions (2D), despite the fact that most taxa use their environments in all 3 dimensions (3D). We (1) created 3D utilization distributions via a multivariate kernel density estimator, (2) adapted 2 overlap indices for use with 3D data, (3) estimated the minimum sample sizes required for accurate estimation of territory size, and (4) assessed these methods using data from American Redstarts (Setophaga ruticilla) during their nonbreeding season in Jamaica. We found that, compared to 3D methods, 2D methods overestimated individual (pairwise) spatial overlap by 3% in scrub habitat and 4% in mangrove habitat. Similarly, 2D methods overestimated total (all neighbors combined) spatial overlap by 9% in scrub and 12% in mangrove habitat. This indicates that American Redstarts may partition territorial space in all 3 spatial dimensions. Moreover, using overlap indices, we found that American Redstarts may avoid areas of overlap, possibly to limit agonistic interactions with neighbors. Although 3D methods require larger sample sizes (80–110 locations) than 2D (40–70 locations), we argue that modeling animal space use in 3D is more realistic and will enhance understanding of niche differentiation, interspecific and intraspecific competition, habitat selection and use, and wildlife conservation.

American Robins (Turdus migratorius) typically eject parasitic Brown-headed Cowbird (Molothrus ater) eggs from their nests. In order to successfully remove parasitic eggs, robins must first differentiate between their eggs and foreign eggs, and then remove the foreign egg(s). Our primary objectives were to determine (1) whether the robins reject cowbird eggs because they are in the minority (“discordancy hypothesis”) or because robins have learned the appearance of their own eggs regardless of whether they form the majority of eggs in the nest (“true egg recognition hypothesis”); and (2) whether the robin's ability to recognize its eggs and reject parasitic eggs was affected by the parasite-to-host egg ratio. We added artificial cowbird eggs to robin nests to create 3 treatments: (1) a majority of robin eggs, (2) an equal number of robin and cowbird eggs, and (3) a majority of cowbird eggs. Parasite-to-host egg ratios were between 1:3 and 3:1. Robins ejected all cowbird eggs at 88% of nests (51 of 58). The frequency of ejection did not differ between the 3 treatments, indicating that robins typically recognized their eggs regardless of whether they were the majority egg type, providing strong support for the true egg recognition hypothesis. However, the risk of ejection for the artificial cowbird eggs was greater as the ratio of cowbird to host eggs increased, which suggests that robins respond adaptively to the increased fitness costs of multiple parasitism. Finally, the risk of ejection of our artificial cowbird eggs was greater later in the nesting season. Because many individuals were exposed to their eggs for the first time early in the season, this result suggests that robins learn to recognize their eggs during their initial nesting attempt.

Northern South America is a geographic bottleneck that may be limiting the survival of Nearctic–Neotropic migrants. However, very little is known about the migration ecology of transcontinental migrants wintering in South America. We studied the fall migratory strategies of three species of thrush (Catharus ustulatus, C. fuscescens, and C. minimus) at 2 major migrant gateways into South America: the Darién and the Sierra Nevada de Santa Marta (SNSM) of northern Colombia. Assuming that migration route shapes the stopover strategy of birds and that our sites receive birds from 2 different routes, we predicted that (1) migrants traveling over land through Central America (Darién) would make short and frequent stopovers followed by short flights and (2) migrants crossing the Caribbean (SNSM) would make few and long stopovers to acquire fuel for longer flights. To test these predictions, we estimated condition on arrival, stopover duration, fuel deposition rates, and potential flight ranges after stopover, using 3 yr of capture–recapture data. Each species adopted a different stopover strategy, with Swainson's Thrush arriving in South America through the Darién, making the shortest stopovers and achieving the shortest flight ranges (800 km); Gray-cheeked Thrush arriving primarily through the Darién, making short stopovers but achieving longer flight ranges (1,200 km); and Veery arriving in both the Darién and the SNSM, making the longest stopovers and achieving the longest flight ranges (1,900 km). Our results suggest that stopover strategies are shaped by both migratory route (over land vs. over water) and distance to final destination in South America. Unraveling the breeding origins and wintering destinations of individuals passing through northern Colombia would greatly improve our understanding of hemispheric migration systems and will be critical if we are to protect the most important stopover sites and habitats.

One of the most commonly estimated parameters in studies of songbird ecology is reproductive success, as a measure of either individual fitness or population productivity. Traditionally, the “success” in reproductive success refers to whether, or how many, nestlings leave nests. Here, we advocate that “reproductive success” in songbirds be redefined as full-season productivity, or the number of young raised to independence from adult care in a breeding season. A growing body of evidence demonstrates interdependence between nest success and fledgling survival, and emphasizes that data from either life stage alone can produce misleading measures of individual fitness and population productivity. Nest success, therefore, is an insufficient measure of reproductive success, and songbird ecology needs to progress beyond this long-standing paradigm. Full-season productivity, an evolutionarily rational measure of reproductive success, provides the framework for appropriately addressing unresolved questions about the adaptive significance of many breeding behaviors and within which effective breeding-grounds conservation and management can be designed.

Investigation of the ecological and evolutionary basis for the often-intriguing courtship behavior of animals requires that we understand the patterns of variation inherent in such behaviors. The courtship displays of the White-ruffed Manakin (Corapipo altera) are not well-known, and previously published descriptions and interpretations of displays conflict with one another. We studied the reproductive behavior of C. altera during 6 breeding seasons, observing 72 display courts (mean 29 ± 2.5 courts annually) for a total of 2688 hr. We updated the behavioral characterization of C. altera by reconciling 8 previous ethologies and describing 2 new behavioral elements, vouchering all with audio and video recordings. We evaluated evidence for the occurrence of male–male cooperation and characterized the physical attributes and temporal dynamics of displays and display courts. We found strong evidence of cooperation among males; 32% of displays for females were highly coordinated displays performed by 2 males, and 8% of those ended in copulation. Males of the highest social status (alphas) retained that status for an average of 1.7 yr (range 1.5 mo to ≥5 yr). Most alphas remained at a single court during their alpha tenure and rarely declined in social status. Only 23% of second-ranked (beta) males transitioned to alpha status, and of those 70% became alphas at a new display court. Display courts did not seem to be limited because few measured physical attributes differed between active display logs and random logs. Several elements of C. altera display behavior and social organization were more variable than in other manakin species, including high turnover of the display courts. This work provides key information for comparative studies investigating the evolution of cooperation in Pipridae.

Growing evidence indicates that producing eggs may constitute a considerable cost of reproduction. If female parental care, which in many species exceeds male performance, is added to these initial costs, it may be concluded that females contribute more to reproduction than males. However, this additional burden on females should reduce their survival and skew the usually equal sex ratio, but this is generally not the case. A resolution of this apparent paradox requires studies estimating the parental investments of both sexes at different stages of breeding, with particular focus on the initial reproductive stage. In the present study, egg composition and its energetic value was estimated in the Dovekie (or Little Auk, Alle alle), a seabird exhibiting bi-parental care except for the end of the chick-rearing period, when the female deserts the brood while the male continues the feeding and escorts the chick during fledging. Condition estimates (size-adjusted body mass and several hematological and biochemical parameters, including concentrations of hemoglobin, glucose, cholesterol, and triglycerides, as well as the leukocyte profile) were also examined in both sexes during the prelaying, laying/relaying, and chick-rearing periods. The egg composition and its energy content indicate that the energetic demands of egg production are not as high as previously assumed, and the non-resource–based costs in females seem to be similar to those experienced by males during the mating period (nest site and/or paternity guarding). However, it was also found that females had lower body mass than males throughout the whole breeding season, suggesting overall female-biased costs of reproduction despite very similar parental performance. This suggests that females are more susceptible to the negative effects of reproduction. If so, their earlier brood desertion may be a response to the additive costs of parental investments.

In many species, individuals benefit from social associations, but they must balance these benefits with the costs of competition for resources. Understanding how these competing factors generate diversity in social systems is a major goal of behavioral ecology, but one that has been hampered by a lack of basic data quantifying many aspects of social structure and associations. Although parrots are generally assumed to have complex social groups, few studies have quantitatively examined these assumptions about parrot social structure. We critically assessed 4 assumptions about parrot socioecology using data from captive and wild groups of Monk Parakeets (Myiopsitta monachus). We evaluated (1) whether pairs are the fundamental unit of parrot social structure, (2) the patterns and extent of fission–fusion dynamics, (3) patterns of aggression and dominance hierarchy structure, and (4) whether individuals share foraging information. We found evidence that supported pairs as the fundamental unit of social structure, although these close associates were not always heterosexual breeding pairs and were sometimes trios. Fission and fusion of subgroups were common, and the amount of fission–fusion dynamics varied across flock types and by fission–fusion dimension, but the amount of variation among dimensions was consistent across replicate captive social groups. Despite these levels of fission–fusion dynamics, study of aggressive interactions in our 2 captive groups indicated that dominance hierarchies existed. Hierarchies were moderately linear (0.7) but not steep (<0.1). Finally, we found no evidence that Monk Parakeets share foraging information among groups through active vocal recruitment to foraging flocks. We compared these patterns with those documented for other species of parrots and other cognitively complex large-brained species. We consider the implications of our results for the study of the evolution of complex sociality and highlight several future directions for parrot socioecology research.

40 Years of Evolution. Darwin's Finches on Daphne Major Island by Peter R. Grant and B. Rosemary Grant. 2014. Princeton University Press. Princeton, New Jersey. xxxii 400 pp., 175 figures. ISBN 978-0-691-16046-7. Cloth, $49.50.