Nest morphology can affect the breeding success of birds. Thus, birds inhabiting different environments may experience divergent selection for nest structure and composition that results in intraspecific geographic variation in nest architecture. We describe interpopulation differences in nest architecture among Thorn-tailed Rayaditos (Aphrastura spinicauda) in 2 contrasting environments near the species' distribution limits: a temperate and very humid environment in north-central Chile (the forest relicts of Fray Jorge National Park; 30°38′S, 71°40′W) and a cold and windy sub-Antarctic environment in the south of Chile (Isla Navarino; 55°4′S, 67°40′W). We collected a total of 62 nests from Fray Jorge and 61 nests from Navarino in 2013 and 2014, measured their dimensions, and quantified their constitutive materials. We tested the nests' thermal properties (simulating heat loss by convection and conduction) and hygroscopic features (water absorption and water loss capacity) and used general linear models to (1) compare these properties between populations and (2) test for a relationship between nest morphology and function. Nests from the northern population exhibited lower rates of heat loss by convection because they were larger and had a lower ratio of surface area to volume; these nests also absorbed less water, probably because of their greater content of plant-derived materials. In the southern population, nests were more compact and better insulated with feathers and hairs, with lower rates of heat loss by conduction. By separately analyzing the roles of convection, conduction, and humidity, our results suggest that potential trade-offs (insulation–humidity) could be differently affecting the nest-building behavior of these populations. Therefore, Thorn-tailed Rayaditos may be using site-specific strategies to cope with the local climate in contrasting environments.

Incubation is a costly phase of avian reproduction, as parents must invest in heat transfer to eggs and nest construction in order to maintain egg temperature within suitable thermal limits; however, costs may differ based on an individual's ability to invest in reproduction. To investigate how environmental conditions, specifically food quality experienced during development and reproduction, influence tactics of resource allocation and costs during incubation, captive Zebra Finches (Taeniopygia guttata castanotis) were raised on either a high- or low-quality diet, paired with a bird of the same diet history, and randomly assigned to breed under the same diet they had been reared on or on the opposite diet. Data were collected on nest attendance, nest quality, nest temperature, and clutch performance (clutch size, egg weight, and number of hatchlings). Greater nest attendance and higher nest-quality scores predicted low temperature fluctuation. Three structural nest components also contributed to temperature maintenance. Temperature fluctuation was the only measure to predict whether or not one or more eggs hatched (“clutch fate”); thus, multiple factors interact to contribute to the outcome of a clutch. Allocation to clutch size and egg mass was influenced only by breeding diet, while nest quality was influenced only by natal diet. In contrast, nest attendance and nest temperature varied with both natal and breeding diets. Nest attendance patterns of birds that experienced a consistently high-quality food environment suggest they faced relatively lower reproductive costs and less sexual conflict than other treatments. Nest temperature patterns of birds raised in a high-quality food environment but bred on a low one suggest they faced higher reproductive costs and more sexual conflict. Thus, a good start in early life may be advantageous if conditions remain favorable, but could lead to higher sexual conflict and reproductive costs if food conditions deteriorate in adulthood.

Climate change during the late Quaternary period (LQP), in both temperate and tropical zones, has been a major driver in the shaping of species distributions and abundances. Our understanding of the various effects of climate change on population dynamics of marine species in temperate zones (such as the Gulf of California) is growing. However, studies on the demographic history of seabirds are rare and there is no description of how regional climate change has affected high-trophic-level marine species such as Heermann's Gull (Larus heermanni; Charadriiformes: Laridae). We investigated whether the demographic history of Heermann's Gull reflects population change consistent with past changes in climate in the Gulf of California during the LQP. We also explored whether those past changes affected the demographic history of codistributed marine organisms in a similar way as found for Heermann's Gulls. To test our hypotheses, we sequenced a fragment of the mitochondrial DNA cytochrome b gene (1,033 base pairs) and performed tests to investigate whether demographic change occurred within the LQP. The results of the 3 approaches used were consistent with a historical demographic expansion during the LQP. All analyses (Fu's F_S test, Tajima's D neutrality test, mismatch distribution analysis [MDA] and associated demographic parameters, and Bayesian skyline plots [BSP]) were consistent with a model of population expansion in Heermann's Gulls. The MDA estimated the expansion event at ∼48,000 yr before present (yr BP; 95% confidence interval: 34,000–72,000), whereas the BSP showed that population growth began ∼100,000 yr BP and lasted until ∼45,000 yr BP. We discuss possible associations between the demographic expansion of this seabird species and large-scale ecological shifts or demographic expansions of other marine species.

Many animals use coloration to signal dominance and fighting ability. In birds, plumage coloration is often linked to individual quality, but less research has investigated coloration in unfeathered traits (i.e. ‘bare parts'), despite theoretical expectations that they might be more reliable signals. Here, we investigate the relationship between multiple ornaments and social dominance in a wild population of the cooperatively breeding Australian Swamphen (known locally as and hereafter referred to as Pūkeko; Porphyrio melanotus melanotus) to test the hypothesis that bare-part ornaments should be more strongly correlated with dominance than plumage coloration. We show that the size and color of the pūkeko's frontal shield (a bare-part ornament), as well as the brightness and chroma of the blue-UV breast plumage, are correlated with social dominance in adult birds. However, the correlation between frontal shield size and dominance was much higher than that between plumage color and dominance, and was also higher than most previously published correlations between plumage traits and dominance. Additionally, frontal shield size, but not breast coloration, was correlated with the size of the testes in male pūkekos, which may be because bare-part ornaments are more closely tied to an individual's current physiology than plumage ornaments. While correlative, our results demonstrate that bare-part and plumage traits could act as redundant ornaments, but with differing reliability, and suggest that future studies on bare-part ornaments will enhance our understanding of dominance signaling.

Brood parasitism is an uncommon and understudied strategy in Amazonian bird communities, within which only 5 species are known to be brood parasites. We present data on the brood-parasitic behavior of the Pavonine Cuckoo (Dromococcyx pavoninus) in 3 host species of small-bodied flycatchers in the Peruvian Amazon that construct hanging globular nests with side entrances. During the 7 yr of the study, we encountered 74 nests of these 3 hosts, but parasitism occurred only in 9 nests (12.2%) in 2 yr. Only 1 Pavonine Cuckoo egg was deposited in each host nest (n = 7), and eggs were markedly dissimilar in size and coloration between hosts and parasite. Incubation investment per day was slightly higher (4%) for 1 parasitized nest than for nonparasitized nests. Overall, 33% of parasitic eggs (n = 6) hatched; cuckoo nestlings apparently removed host eggs and killed host nestlings. The nestling period lasted 24 days, and the growth-rate constant based on nestling mass (k = 0.23) was slower for parasite nestlings than for their hosts (k = 0.27 and 0.31). Food provisioning rates were greater in 1 parasitized nest (2.1 ± 0.7 feedings hr⁻¹ nestling⁻¹) than in nonparasitized nests (1.1 ± 0.4). Nestling cuckoos may further mimic the plumage of their host nestlings. Our results suggest that Pavonine Cuckoos negatively affect their hosts' breeding success and are engaged in a coevolutionary arms race with hosts that have defenses against parasitism.

Many brood parasites rely on mimicry to prevent the detection of their eggs by hosts, yet most Australasian cuckoo species lay darkly colored eggs while the eggs of their hosts are pale and speckled. In the dimly lit nests of their hosts, these cuckoo eggs may appear cryptic; however, it is unclear if this disguise has evolved to fool hosts or other cuckoos. Recent work suggests that in at least one species of bronze-cuckoo, cuckoos are more likely to reject conspicuous eggs than are hosts, but it remains unclear whether this is common across the species group. Here, we present field experiments on the sole host of the Shining Bronze-Cuckoo (Chalcites lucidus lucidus) in New Zealand, the Grey Gerygone (Gerygone igata; known locally as the Grey Warbler), that explored whether this host ignores cuckoo eggs because they are cryptic. Using an avian vision model, we showed that Shining Bronze-Cuckoo eggs were variable in their conspicuousness, but were more cryptic in host nests than the host's eggs. We then experimentally parasitized all available clutches with model eggs that mimicked darkly or brightly colored cuckoo eggs, or were of maximum conspicuousness (white) as determined by visual modeling. Hosts never rejected our model eggs, nor cuckoo eggs when naturally parasitized. Instead, only cuckoos rejected model eggs: In 3 out of 4 experimental nests that were subsequently parasitized, the model egg was taken and replaced by a cuckoo's egg. Together, these data and previous experiments suggest that competition among cuckoos, rather than rejection by hosts, provides a stronger selection pressure for the evolution of cryptic eggs across the genus Chalcites.

Obtaining unbiased survey data for vocal bird species is inherently challenging due to observer biases, habitat coverage biases, and logistical constraints. We propose that combining bioacoustic monitoring with unmanned aerial vehicle (UAV) technology could reduce some of these biases and allow bird surveys to be conducted in less accessible areas. We tested the feasibility of the UAV approach to songbird surveys using a low-cost quadcopter with a simple, lightweight recorder suspended 8 m below the vehicle. In a field experiment using playback of bird recordings, we found that small variations in UAV altitude (it hovered at 28, 48, and 68 m) didn't have a significant effect on detections by the recorder attached to the UAV, and we found that the detection radius of our equipment was comparable with detection radii of standard point counts. We then field tested our equipment, comparing songbird detections from our UAV-mounted recorder with standard point-count data from 51 count stations. We found that the number of birds per point on UAV counts was comparable with standard counts for most species, but there were significant underestimates for some—specifically, issues of song masking for a species with a low-frequency song, the Mourning Dove (Zenaida macroura); and underestimation of the abundance of a species that was found in very high densities, the Gray Catbird (Dumetella carolinensis). Species richness was lower on UAV counts (mean = 5.6 species point⁻¹) than on standard counts (8.3 species point⁻¹), but only slightly lower than on standard counts if nonaudible detections are omitted (6.5 species point⁻¹). Excessive UAV noise is a major hurdle to using UAVs for bioacoustic monitoring, but we are optimistic that technological innovations to reduce motor and rotor noise will significantly reduce this issue. We conclude that UAV-based bioacoustic monitoring holds great promise, and we urge other researchers to consider further experimentation to refine techniques.

In birds, both males and females can exhibit socially selected traits, but relatively few studies address the role of female ornaments despite their potential importance in competitive female–female interactions and male mate choice. We investigated the melanized plumage pattern of male and female Spotted Sandpipers (Actitis macularius), a species with sex-role reversal and a polyandrous mating system. While the sexes overlap in the spottiness metrics, females had fewer, but larger and more irregularly shaped spots that covered a greater percentage of their plumage than did males. Feather mite load best explained the first principal component of plumage pattern (i.e. spot size) in females as well as in males. Sandpipers with lower mite loads had larger spots, but this relationship was less strong in males. Considering the second principal component (i.e. spot shape and percent cover), mass, hematocrit levels, and day captured best explained variation across females. Heavier females with higher hematocrit levels were caught later in the season and had more irregular spots and a higher percentage of melanized plumage cover. Spot pattern in recaptured individuals changed with capture year, indicating that spottiness varies within an individual's life. Overall, these results show that although the differences between the sexes are subtle, spottiness in Spotted Sandpipers is a measurably sexually dimorphic trait with females as the more ornamented sex, and that melanized ornaments can be indicators of female, and possibly male, condition.

We describe Scytalopus alvarezlopezi from the Western Andes of Colombia. The new species forms part of a distinctive clade of Scytalopus tapaculos (Rhinocryptidae) that also includes S. robbinsi from Ecuador and S. stilesi and S. rodriguezi, which occur on the Central and Eastern Andes of Colombia. S. alvarezlopezi is easily diagnosable from its near relatives by its song and mitochondrial DNA; differences in plumage exist but are more subtle. The species inhabits dense understory vegetation on the floors and lower slopes of ravines in cloud forest at elevations of 1,300 to 2,100 m. On the Pacific slope, its altitudinal distribution is sandwiched between those of S. chocoensis (below) and S. vicinior (above); the latter in turn is replaced higher up by S. spillmanni and S. latrans, but S. alvarezlopezi also occurs at ∼2,000–2,100 m on eastern slopes just below the low ridgeline. All of the latter species are distinguished by vocal and plumage characters. Marked sexual differences in plumage exist in stilesi, but females have yet to be collected for alvarezlopezi and rodriguezi. We consider that S. alvarezlopezi is not threatened at present, but could be potentially vulnerable due to its restricted distribution; it is endemic to Colombia.

The avian world is packaged into genetic assemblages that we call species. Although ornithologists can, with a few important exceptions, agree on the boundaries among avian gene pools that delimit species, the evolutionary process that created this structured subdivision of Aves remains uncertain and contentious. Moreover, although avian species are recognizable and diagnosable, many bear signatures of recent, often substantial, exchange of nuclear (N) genetic material. As a result, there is debate regarding the process that gives rise to and maintains the genetic structure of avian populations. I propose that a key missing consideration in discussions of speciation is the necessity of coadaptation between N and mitochondrial (mt) genes to enable core energy production via oxidative phosphorylation. Because mt genomes are non-recombining and subject to high mutation rates, they evolve rapidly. Consequently, N and mt coadaptation persists only through perpetual coevolution between mt and N genes. Mitonuclear coevolution leads to rapid divergences in coadapted mitonuclear gene sets whenever there is a disruption in gene flow among populations. As a result, once populations diverge in coadapted mitonuclear genotypes, the reduced fitness of offspring due to mitonuclear incompatibilities prohibits exchange of mt and N-mt genes and effectively isolates individuals with shared coadapted N and mt genotypes. Given these considerations, I propose that avian species can be objectively diagnosed by uniquely coadapted mt and N genotypes that are incompatible with the coadapted mt and N genotype of any other population. According to this mitonuclear compatibility species concept, mitochondrial genotype is the best current method for diagnosing species.

Kin selection theory predicts that extrapair mating should be rare in cooperatively breeding birds. However, most cooperative breeders are not genetically monogamous and the relationship between promiscuity and cooperative breeding remains unclear. This relationship is further complicated by a lack of data. The majority of cooperatively breeding birds live in the tropics, and their genetic mating systems are little known. Here we studied the genetic mating system of the Grayish Baywing (Agelaioides badius), a socially monogamous Neotropical blackbird in which most nesting pairs are assisted by helpers, previously assumed to be offspring of the breeding pair. Grayish Baywings are the primary host of the parasitic Screaming Cowbird (Molothrus rufoaxillaris), and previous studies have found a positive association between brood parasitism and helper recruitment in the last part of the nestling period. We used microsatellite markers to analyze the kinship of 192 individuals in 47 breeding groups, finding that 13% of 153 nestlings (in 38% of 47 nests) resulted from extrapair mating. We also documented 2 instances of conspecific brood parasitism and 1 instance of quasiparasitism (the nestling was sired by the social father, but was unrelated to the social mother). Of 8 helpers that were genotyped, 4 (all males) were offspring of the breeding pair and 4 (2 males, 2 females) were unrelated to both members of the breeding pair. None of the helpers produced offspring within the clutch. These results suggest that, although cooperative breeding is frequent, genetic relatedness between Grayish Baywing helpers and the offspring that they raise is highly variable. Future studies are needed to determine why unrelated helpers assist at Grayish Baywing nests, and to understand the role that brood parasitism may have played in the evolution of cooperative breeding in this species.

Visual foragers joining mixed-species flocks can enhance foraging and obtain antipredator benefits. However, relatively little is known about the benefits that tactile foragers may obtain by joining mixed-species groups. We investigated the foraging and antipredator benefits that the Crested Ibis (Nipponia nippon), an endangered species, may get while foraging in single-species flocks and in mixed-species flocks with Little Egrets (Egretta garzetta) during the nonbreeding season. We found that in single-species flocks ibises decreased the proportion of time spent vigilant and increased that spent foraging as total flock size increased. Flight initiation distance (FID, distance between a threat and the animal when the latter flees) decreased with flock size particularly in single-species flocks and alert distance (AD, distance between a threat and the animal first exhibiting alert behavior) decreased with flock size in both single- and mixed-species flocks, but was greater in mixed-species flocks. Taken together, these findings suggest that Crested Ibises may use risk dilution, but not collective detection, in single-species flocks, but use dilution, collective detection, and early warning in mixed-species flocks. We also found partial support for the resource exploitative competition hypothesis as probing bout duration increased with flock size. This tactile forager may benefit from joining mixed-species flocks with a visual forager by using collective detection and early warning (responding to the antipredator signals of the other species), but also tolerate some intraspecific competition in mixed-species flocks through resource depletion effects. Our findings have management implications that could be applied to the protection of this endangered species.

In most avian species, egg-turning behavior during incubation is vital for proper embryonic development and hatching success. However, changes in turning behaviors are rarely studied across different temporal scales (e.g., day–night or across incubation phases), though the timing of incubation behaviors affects reproductive success. We used data loggers encapsulated in artificial eggs to measure turning rates and angle changes of eggs in Western Gull (Larus occidentalis) and Laysan Albatross (Phoebastria immutabilis) nests. We examined diurnal and daily cycles in egg-turning behaviors across early, middle, and late incubation phases. Our results indicate that (1) egg-turning behaviors remain similar throughout incubation, resulting in a consistent environment for developing chicks; (2) egg-turning rates and angle changes vary according to diurnal cycles and day length in each species; and (3) egg-turning rates, but not angle changes, were similar between species. Egg-turning behaviors may vary among species according to seasonality and geography, and using consistent methodologies to measure egg turning will further clarify the role of egg turning in avian life history and ecology.

Altitudinal bird migration involves annual seasonal movements up and down elevational gradients. Despite the fact that species from montane avifaunas worldwide engage in altitudinal migration, the patterns, causes, and prevalence of these movements are poorly understood. This is particularly true in North America where the overwhelming majority of avian migration research has focused on obligate, long-distance, temperate–tropical movements. Elsewhere in the world, most altitudinal migrants are partial migrants, making downhill movements to nonbreeding areas. However, spatial and temporal patterns, the prevalence and predictability of migration at individual and population levels, and the ultimate ecological factors selecting for movement behavior vary considerably among taxa and regions. I conducted a systematic survey of the evidence for altitudinal migration to fill gaps in our understanding of this behavior among the landbirds of North America and Hawaii. Altitudinal migration was as prevalent as in other avifaunas, occurring in >20% of continental North American and nearly 30% of Hawaiian species. Of the species wintering within the USA and Canada, ∼30% engage in altitudinal migrations. Altitudinal migrants are far more common in the West, are taxonomically and ecologically diverse, and North American species exhibit patterns similar to altitudinal migrants elsewhere in the world. Because altitudinal migration systems are relatively tractable, they present excellent opportunities for testing hypotheses regarding migration generally. Altitudinal migration has likely been overlooked in North America due to contingency in the history of ornithological research. Our need to understand the patterns and causes of altitudinal migrations has never been greater due to emerging environmental threats to montane systems.

Feathers serve numerous functions, from flight to interspecific and intraspecific communication. Melanin has been shown to protect feathers from microbial degradation that might, for example, hinder flight or mate attraction. Most studies have focused on the physical resistance to degradation that melanin provides. However, it has yet to be addressed whether melanin alters bacterial colonization and attachment patterns before degradation. We used the common keratinolytic bacterium Bacillus licheniformis to test for preferential attachment and colonization on feathers with black (melanized) and white (unmelanized) stripes. Using experimental inoculation of Eurasian Three-toed Woodpecker (Picoides tridactylus) feathers in vitro and scanning electron microscopy, we show that B. licheniformis preferentially colonizes white feather stripes nearly twice as often as black feather stripes. These data suggest that melanin, in addition to strengthening feathers, may inhibit colonization of keratinolytic bacteria, with possible implications regarding the mechanisms of exceptional preservation of feathers and melanin in the fossil record.