Molecular measures of parentage provide important insights into the opportunity for sexual selection; in birds, such studies have been conducted almost exclusively on pair-bonded passerines. Here I employ a multitiered parentage analysis involving 10-locus microsatellite genotypes to characterize the genetic mating system of a population of Wild Turkeys (Meleagris gallopavo), a promiscuous species in which males and potentially females have been thought to mate multiply. Young in almost half of nests (48%, n = 15) were each apparently the product of a single male and female parent. Fourteen broods (45%) resulted from multiple paternity; seven contained eggs from multiple females, four of which appeared to be cases of quasi parasitism, in which the offspring of the brood parasitic female were fathered by the same male that sired at least one of the host females' offspring. Bateman gradients for males and females indicate that males experience a significantly greater gain in reproductive success from additional mates; the trend for females to benefit from multiple matings disappeared when the small “clutches” of parasitic females were excluded from the analysis. Of the components of variance in male fitness, number of mates was the most important determinant of male reproductive success. Somewhat surprisingly, when considering only reproductively successful males, the proportion of a female's offspring that a male sired also explained a substantial proportion of the total variance in male reproductive success. Incomplete sampling of offspring could mean that these estimates, particularly the importance of mate number, may be underestimated. Regardless, these results suggest that multiple mating by females may be an important and overlooked component of sexual selection in species with lek-like mating systems, and that selection may act independently on males to attract more mates and increase their share of paternity with those mates.

Individuals are predicted to direct aid-giving behaviors preferentially to kin. In this study, we examined patterns of investment in nesting activities and compared them to genetic paternity across a three-year period (1994–1996) in cooperatively breeding Brown Jays (Cyanocorax morio) in Monteverde, Costa Rica. Brown Jays live in large, territorial groups (mean = 10 individuals) that usually contain a single primary nesting female, her social mate (consort), and helpers of both sexes. Consorts were identified in most but not all nesting female-years; the consort–breeding female relationship was a stable one that often persisted across years, and consorts spent more time with the breeding females than did any other group males during nest building and egg laying. At an individual level, helpers invested little time in the nest area or feeding effort during the prenestling stages, although they provided the majority of feedings (90%) to the breeding female. The breeding pair spent more time in the nest area and had higher nestling feeding rates than the helpers. Consorts did not reduce their investment in nestling feeding in cases where they had not obtained paternity. Within-group extra-pair fathers, on the other hand, tended to provision nestlings less than did other nonbreeding males and were very rarely seen in the nesting areas. Extra-group fathers provided no nestling care. Brown Jay consorts appear to invest less in nesting activities compared to other well-studied New World jays. These findings suggest that mate guarding may be ineffective for consorts, and that both consorts and helper males may invest little in nesting activities because they are pursing mating or dispersal opportunities outside their social groups.

We tested the potential for social selection to act as a mechanism driving rapid plumage divergence in two sympatric monarch flycatchers, the White-capped Monarch (Monarcha richardsii) and the Kolombangara Monarch (M. browni), endemic to a single island group in the Solomon Archipelago. Solomon Island monarchs are famous for dramatic patterns of morphological divergence across very narrow water gaps, little parallel ecological variation, and minimal genetic differentiation among sister taxa inhabiting adjacent island groups. Social selection theory predicts that plumage traits evolved in allopatry may transmit important social information and that responses of dimorphic and monomorphic taxa to territorial intrusions will differ. For the dimorphic M. richardsii, we presented mounted specimens of subadult or female—and adult male—plumaged individuals to territorial birds and quantified their responses to these simulated intrusions. Territorial male M. richardsii generally responded alone, reacting most aggressively to adult male mounts. This response suggests that the bright white cap and occipital and nape patches on male M. richardsii function as social signals. In contrast, in the monomorphic M. browni, both sexes responded aggressively to intrusions of an adult-plumaged conspecific mount. Furthermore, in a variety of Melanesian forest passerines, individuals of dimorphic species generally responded singly to simulated territorial intrusions, whereas individuals of monomorphic taxa usually responded in pairs. Together, these data suggest social selection may be an important mechanism of population divergence driving some of the most extreme patterns of geographic variation among birds.

With more than 50 described subspecies occurring throughout Southeast Asia and Micronesia and a wide array of morphological and ecological variation, the Island Thrush (Turdus poliocephalus) is one of the most variable known bird species. However, this bird has been studied surprisingly little from an evolutionary perspective, with no information on its evolutionary history to inform our understanding of its tremendous variation. In this study, we examine the population history of the Island Thrush within the Philippine Islands, sampling 88 individuals from six named Philippine subspecies and three populations currently lacking formal subspecific names, as well as several outgroups. Many subspecies are not reciprocally monophyletic, yet most island populations are, and show up to 2.6% sequence divergence (uncorrected). Philippine populations are not monophyletic; samples from Borneo, Sulawesi, Vanuatu, and the Solomon Islands are nested within the Philippines. Previously hypothesized routes of the colonization of the Philippines assume a single initial colonization event and cannot account for the current distribution of haplotypes, which implies at least two colonization events. Morphologically similar taxa in the Philippines are not each other's closest relatives, thus demonstrating plumage convergence. We emphasize the need for further study of this taxon throughout its range, particularly in light of conservation priorities.

I used a robust design to model the influence of age, sex, climate conditions, and chick body mass on the annual survival of the Mountain Plover (Charadrius montanus) in north-central Montana from 1995–2006. I found evidence that chick age predicted body mass (i.e., log₁₀ (mass) = 0.03 × age 1.02) and subsequently modeled juvenile survival as a function of body mass. Juvenile survival was similar for both sexes and was positively influenced by body mass at capture. The predicted annual survival for a juvenile plover from date of hatching (10 g) was 0.06 (95% CI was 0.02, 0.15) and increased with body mass. Annual survival was similar for adults of both sexes and ranged from 0.74 to 0.96 yearly. There was a hint that male survival was higher than that of females, although this effect was weak. Adult survival was affected by a Palmer Modified Drought Index that measured local climate conditions and indicated that annual survival was highest during drought periods. Implications of this study include understanding the processes influencing annual survival in a declining species, providing a basis for long-term population projections, relating demographic processes to climate change, and increasing our knowledge of survival patterns among the Charadriidae.

Whereas demographic performance increases with experience, little is known about the experience-related response of demographic performance to environmental variations. In long-lived birds, theoretical studies consider experience-related differences in performance to be greater under more restrictive conditions, but this has rarely been tested. We tested this hypothesis on the White Stork (Ciconia ciconia), using a long-term capture-mark-recapture dataset. We studied the demographic response of a population from Western Europe to climate by analyzing adult survival and breeding success as a function of breeding experience. Birds reproduced less well during their first breeding event than during subsequent ones, suggesting that they undergo a learning process. In addition, high mortality in storks inexperienced at breeding may reflect an important cost associated with the first reproduction event. Presumably, birds subject to the highest cost of reproduction would die during the ensuing winter, with selection favoring birds able to maximize their survival. The first reproductive occasion could be considered a key event for White Storks, for whom mean breeding performance as well as survival probability increased over time in the population, likely as a result of a combination of learning and selection processes. Interannual variation of breeding success was partly explained by spring precipitation on the breeding ground, reflecting environmental variation. By contrast, winter conditions in the Sahel could not explain fluctuations of the survival. Contrary to our predictions, over this 12-year study, inexperienced individuals seemed to be affected by climatic fluctuations, regardless of their severity, in the same manner as experienced ones.

The Buff-breasted Sandpiper (Tryngites subruficollis) is a shorebird of conservation concern whose migration patterns and population size are poorly known. We conducted surveys in the Eastern Rainwater Basin, Nebraska, in 2004 and 2005 using distance sampling. This survey produced density estimates of 0.09 birds per ha in 2004 and 0.04 birds per ha in 2005. Because the study area was explicitly defined by soil characteristics, we were able to extrapolate from density estimates to produce predictions of overall numbers in the study area. We produced minimum estimates of the numbers of Buff-breasted Sandpipers stopping over in the region—43 300 in 2004 and 22 924 in 2005. When we restricted our predictions to only the area adjacent to roads, numbers of birds ranged from 13 488 to 41 513, depending on the area used. These predictions indicate two important findings—that 1) the current estimate of the world population of Buff-breasted Sandpipers of 15 000 to 20 000 individuals is too low, and 2) the Eastern Rainwater Basin appears to be a primary spring stopover site for the species in the North American Great Plains.

We studied density changes of two groups of Neotropical austral migrant landbirds—the South American temperate-tropical (SATT) and cold-temperate (SACT) migratory systems—in the main habitat types of the central Monte desert of Argentina (open Prosopis flexuosa woodland and Larrea cuneifolia shrubland) over 10 years. Five species, all tyrant flycatchers (Tyrannidae) made up SATT, whereas only two of the seven species of SACT were tyrannids. Densities of both SATT and SACT were higher in open woodland than in shrubland. SATT density did not differ among years, but SACT density did, having lower values in 1994 in both habitats. In subsequent years, SACT densities increased but did not reach values similar to those previous to 1994. The decline in 1994 coincided with a two-year drought period that began in 1993, but lower density in the following years did not appear to be related to climatic conditions in the study area, suggesting a low capacity of SACT species to recover population abundance after periods of stress. In contrast, SATT density was not associated with local climatic conditions, possibly because several SATT species used the study area only as a stopover site. During the breeding season, birds of both migratory systems disproportionately use the open woodland, which offers more sites to nest and feed than does the shrubland. Although most SATT and SACT species are abundant and not currently of conservation concern, human activities in the central Monte desert promote the structural simplification of the habitat, which could threaten future populations of Neotropical austral migrant landbirds in this ecosystem.

Cavity-nesting communities can be viewed as interconnected webs that interact through the creation of and competition for cavities as nest sites. Using a web approach, we depicted the flow of cavity creation and use in the cavity-nesting bird community of a Florida longleaf pine (Pinus palustris) ecosystem to examine the relationship between cavity-nesting bird abundance and cavity resources, and to identify species with potential to respond to cavity management for the endangered Red-cockaded Woodpecker (Picoides borealis). We identified two groups into which most cavity-nesting species could be placed: 1) six species associated with pine snags and Red-cockaded Woodpecker cavities, and 2) five species associated with hardwood snags. We found the majority of nests (60%) in large pine snags. Red-cockaded Woodpeckers and Northern Flickers (Colaptes auratus) excavated most cavities used by other cavity nesting birds. The Northern Flicker was the primary creator of large nest cavities, through its excavation in snags and enlargement of cavities originally excavated by the Red-cockaded Woodpecker in live pine. Large secondary cavity nesting birds were the primary users of Red-cockaded Woodpecker cavities, and we identified three cavity-nesting species with potential to respond to Red-cockaded Woodpecker cavity management. The cavity-nesting web dynamics documented in this study, including the role of large pine snags, Red-cockaded Woodpecker cavities in live pine, and excavating species within the community, can serve as a baseline for comparison to other southern pine forests.

Open-ended learning of flight calls has been found consistently in the subfamily Carduelinae. Understanding call learning is especially important in Red Crossbills (Loxia curvirostra complex) because calls appear to play an instrumental role in assortative mating, perhaps by acting as a marker trait that signals ecological adaptation for foraging on a particular species of conifer. We analyzed flight call recordings from a banded population of the South Hills (call type 9) crossbill to examine whether young birds imitate the calls of their parents and whether, as adults, individuals modify their calls to match those of their mates. The calls of offspring were more similar to the calls of their parents than to the average adult in the population. This indicates that calls are, at least initially, culturally inherited from parents and thereby could act as marker traits. Adults did later modify their calls to match the calls of their mates, which presumably aids in individual and pair recognition. Comparisons within individuals over time also showed that call structure decreased in similarity to the calls of crossbills with another type of call (type 2) that regularly occur in the South Hills of Idaho. This should make it easier for individuals to distinguish between individuals of different call types. However, one of 91 crossbills recorded over more than one year changed the type of its call. This type 2 female bred successfully with a type 9 male for two years and by the second year changed her call to match that of her type 9 mate.

Variation in song can play a central role in species and subspecies recognition among birds. The ability of individuals to distinguish between songs of their own versus songs of a different subspecies potentially strengthens local adaptation of subspecific populations. We investigated the degree of vocal divergence and discrimination between two subspecies of Swamp Sparrow (Melospiza georgiana) to examine how variation in song could influence behavioral response. We recorded songs of Southern (M. g. georgiana) and Coastal Plain (M. g. nigrescens) Swamp Sparrow males in Maryland and Delaware, respectively, and analyzed variation in syllable composition, repertoire size, trill rate, and frequency bandwidth. In addition to describing differences in song characteristics, we performed an estimate of local song type diversity that predicted larger population repertoires in M. g. nigrescens. We then broadcast recordings to evaluate male territorial responses to song and found that males reacted more strongly to songs of their own subspecies than to songs of the other subspecies. The extent of song variation and discrimination suggests the possibility of continued divergence. Further tests may determine whether such results can be generalized beyond the populations studied to the subspecies level, and whether females as well as males differentiate between songs from separate subspecies.

We show that free-ranging Laughing Kookaburras (Dacelo novaeguineae), the largest kingfishers, are heterothermic. Their minimum recorded body temperature (T_b) was 28.6°C, and the maximum daily T_b range was 9.1°C, which makes kookaburras only the second coraciiform species and the only member of the Alcedinidae known to be heterothermic. The amplitude of nocturnal body temperature variation for wild, free-living kookaburras during winter was substantially greater than the mean of 2.6°C measured previously for captive kookaburras. Calculated metabolic savings from nocturnal heterothermia were up to 5.6 ± 0.9 kJ per night. There was little effect of ambient temperature on any of the calculated T_b-dependent variables for the kookaburras, although ambient temperature did influence the time that activity commenced for these diurnal birds. Kookaburras used endogenous metabolic heat production to rewarm from low T_b, rather than relying on passive rewarming. Rewarming rates (0.05 ± 0.01°C min⁻¹) were consistent with those of other avian species. Captivity can have major effects on thermoregulation for birds, and therefore the importance of field studies of wild, free-living individuals is paramount for understanding the biology of avian temperature regulation.

Nest placement affects the risk of predation on both eggs and incubating parents and determines the microclimate for incubation, two functions that may be in conflict, especially in hot deserts. We studied the roles of microclimate and nest predation on nest site selection by Hoopoe Larks (Alaemon alaudipes) in the Arabian Desert. Hoopoe Larks build nests in three microsites: on the gravel plain away from vegetation, at the base of bushes, or above ground in bushes. Early in the breeding season, 70% of nests were placed on the ground, but as the season progressed, nests in small bushes represented 77% of total nests; nest cover increased from 5% to 21%. Daily survival rate of natural nests was 0.82. Predation on eggs did not differ among nest sites, either for natural nests or in an experiment with artificial nests. Measurements of operative and egg temperatures showed that artificial nests on the gravel plain experience higher temperatures than those under and in bushes. Nest attendance totaled 77% of daytime in nests under bushes and 81% in nests in or on top of bushes, with the larger share of attendance contributed by females. However, during midday, when evaporative water requirements—estimated from temperature profiles at artificial nests—were 10–15-fold higher than during early morning, males and females shared incubation duties almost equally. We hypothesize that Hoopoe Larks favor exposed nest sites to reduce predation risk to themselves as incubating parents, but as the season progresses, they select nest sites with more cover at the base of or within bushes because the thermal environment forces them to do so.

Little is known about the role that hormones play in controlling the life cycles and behaviors of resident, tropical-forest passerines. In this study, we document levels of the sex hormones dihydroepiandosterone (DHEA), estradiol, luteinizing hormone (LH), progesterone, and testosterone in male and female Song Wrens (Cyphorhinus phaeocephalus) during the breeding season. In males, we found no significant seasonal changes in sex hormones and no effect of molt or experimental social challenge on hormone levels. The lack of population-level variation in sex hormone levels throughout the reproductive season highlights the asynchronous nature of reproduction in this species. Stimulation of the hypothalamo-pituitary-gonadal axis through injection of gonadotropin-releasing hormone (GnRH) did not affect sex steroid levels in males but did cause a significant increase in LH levels. Low basal testosterone levels in males and the failure of males to respond to GnRH or social challenge with an increase in testosterone indicates either a limited role for systemic testosterone or a system highly sensitive to small changes in hormone titers. Levels of LH, progesterone, and testosterone were similar in females with and without active brood patches, though DHEA levels were higher in females with them. As in males, reproductive hormone levels in females did not change with body or wing molt. However, although wing molt was not significantly related to brood patch status, body molt was negatively associated with the presence of active brood patches in females. This result may suggest an inability of females to engage in body molt and breeding simultaneously.

Ectoparasites are a common component of seabird colonies and are generally considered to have a negative impact on their hosts. Nest parasites such as the soft tick Carios capensis may pose a distinct threat to altricial nestlings confined to the nest and unable to escape infestation. To assess the potential effects of ticks on growth, we measured linear growth rates of Brown Pelican (Pelecanus occidentalis) nestlings during early development in relation to C. capensis infestation at insecticide treated and untreated nests at two colonies in South Carolina during the 2004 and 2005 breeding seasons. Tick infestation levels differed between colonies but not between years. We found a positive relationship between tick infestation and both growth rates and hatching success at the more infested colony. We did not find a consistent relationship between insecticide treatment and growth rates, although chicks from nests treated with insecticide had fewer ticks compared to chicks from untreated nests. Our study suggests that the cohabitation of ectoparasites and seabirds within colonies may result in behavioral or physiological adaptations of adults or nestlings that inhibit the expected negative effect of ectoparasites on nestling growth at sublethal levels of infestation.

Obligate brood parasites should synchronize parasitism with host laying to maximize egg hatchability and chick survival. While the generalist Shiny (Molothrus bonariensis), Brown-headed (M. ater), and Bronzed (M. aeneus) Cowbirds frequently synchronize parasitism with host laying, specialist Screaming Cowbirds (M. rufoaxillaris) very often fail to do so in nests of their main host, the Bay-winged Cowbird (Agelaioides badius). The poor synchronization of Screaming Cowbird parasitism may be the result of low availability of host nests at the time of laying, higher nest attentiveness by the host during laying, or unpredictable host laying behavior. We used a large set of observational data to test these hypotheses. The rate of Screaming Cowbird parasitism occurring during host prelaying was 31%, while during laying and incubation, it was 50% and 19%, respectively. Synchronization of parasitism was not associated with availability of host nests at laying or with changes in host nest attentiveness through the nesting cycle. The length of the prelaying period varied from one to 19 days and was not associated with latency of parasitism after nest completion. Nests with prelaying periods of 4–6 days received fewer eggs than nests with shorter or longer periods. Shiny Cowbirds also parasitized Bay-winged Cowbirds during prelaying more frequently (48%) than in other studied hosts (1%–8%). Our results indicate that Bay-winged Cowbird prelaying behavior precludes synchronization between parasitism and host laying and therefore may act as an antiparasitic defense, as it decreases the incidence of successful parasitism.

We studied sex differences in collision mortality in adult Common Terns (Sterna hirundo) at a wind farm in the direct vicinity of a breeding site in Zeebrugge, Belgium in 2005–2007. In total, 64 fatalities were collected and sexed, of which 64% were males. Uneven sex ratio among these birds was most pronounced during the period of incubation and early chick feeding (15 May–15 June), when 78% of the 28 mortalities were male. During prelaying and feeding of young, the sex ratio of mortalities did not differ from equality. We argue that sex-biased collision mortality in Common Terns does not result from morphological differences between the sexes, but rather reflects differences in foraging frequency between males and females during egg-laying and incubation.

Hurricane landfalls pose a potential threat to coastal landbird populations. The effects of Hurricane Katrina's landfall in August 2005 on the suburban and urban resident landbird community of Greater New Orleans, Louisiana was assessed beginning five weeks after landfall. Compared to numbers tallied during surveys from 1994 to 2000 on 2.2 km of transects, the 10 most numerous bird species all showed strong declines, as did tree squirrels (Sciurus spp.). Additional transect surveys at 100 random locations citywide showed the overall bird numbers on the initial 2.2 km to be similar to those in the city overall. Additional surveys conducted in the Lower Ninth Ward, Arabi, and the site of the Murphy Oil spill showed numbers of birds to be extremely low in these especially heavily affected areas. The impact of the oil contamination was difficult to assess, with bird numbers low, but not obviously lower than in uncontaminated areas.

Wing loading, defined as the ratio of body mass to wing area, is a critical phenotype affecting flight. In the House Sparrow (Passer domesticus), wing loading is optimized, and both the mean and variation in body mass are inverse functions of ambient temperature. Combined, these relationships predict that climatically induced changes in body mass under optimized wing loading must be countered by directional and variance selection on wing area. Measuring multiple North American House Sparrow populations sampled throughout the 20th century, I show that observed sex-specific changes in the mean and variation in wing length (a close proxy of wing area) are related to changes in winter temperature and quantitatively predicted from a model where wing loading is optimized.

Alexander Skutch suggested that the threat of nest predation on tropical birds favors reduced activity near their nests. This hypothesis assumes that nest predation occurs during the day when adult birds are active, but few studies of tropical species have reported distributions of nest losses during the day-night cycle. We used thermistors placed in nests to record the time of nest predation events for species of understory rainforest birds during the incubation period. In our study, 14 of 21 nest-predation events (67%) occurred between 11:00 and 18:00 (EST), and none took place at night, between 19:00 and 06:00. Clearly, nest predation during incubation was primarily diurnal. Although a major premise of Skutch's hypothesis is supported, further research is needed to determine whether diurnal predators are attracted to nests by the movements of parent birds, begging of offspring, or other cues.

The Great-tailed Grackle (Quiscalus mexicanus) and Boat-tailed Grackle (Q. major) are sister species that have expanded their ranges during historical times. This expansion has created an area of sympatry between these species in Texas and Louisiana, and between distinctive Great-tailed Grackle subspecies in the southwestern United States and northern Mexico. We investigated the evolutionary histories of both species using mitochondrial DNA sequence data and modern phylogenetic methods. Our results reveal genetic structure within Great-tailed, but not Boat-tailed Grackles. Great-tailed Grackles are separated into two clades, but range expansion in the north has led to secondary contact between them. Boat-tailed Grackles are monophyletic and are embedded within the Great-tailed Grackle assemblage, rendering the latter paraphyletic. These results reveal a complex phylogeographic pattern caused by recent range expansion and secondary contact of once allopatric units.

Nantucket Island, Massachusetts, hosts the largest population of breeding Northern Harriers (Circus cyaneus) in the northeastern United States. We analyzed 128 nest sites to determine landscape features influential to habitat selection. We performed a vegetation community use-availability study, and we used 70 GIS-derived landscape metrics to conduct a classification tree analysis. We used the classification tree results to quantify, predict, and map the preferred nesting habitat of harriers islandwide. The vegetation community use-availability study showed that harriers had a preference for herbaceous marsh and shrublands and that they used low vegetation and forested habitats less than expected by availability. Preferred nesting habitat had two classification nodes. The first node represents habitat distant from developed land and roads, out of forests, and in or immediately adjacent to wetlands. The second node represents habitat identical to the first node with respect to distance from high densities of development and forests, but is upland and contains only minimal developed land. We applied the classification tree's criteria to GIS data for the entire island to create an islandwide map of preferred nesting habitat. Although most of the island's preferred nesting habitat is currently preserved (86%), we suggest conserving the remaining unprotected areas to maintain important nesting habitats.

We measured provisioning and growth patterns in Bald Eagle (Haliaeetus leucocephalus) chicks from nests in two salinity zones in the lower Chesapeake Bay. Nestlings in mesohaline reaches experienced higher per capita consumable energy provisioning rates and had higher instantaneous growth rates compared to nestlings in tidal-fresh salinity zones. These results suggest that Bald Eagles nesting along mesohaline reaches are more successful at meeting the energetic demands of brood rearing compared to pairs nesting along tidal-fresh reaches, a finding consistent with documented higher reproductive rates and proportion of three-chick broods along mesohaline reaches compared to tidal-fresh reaches. The results of this study have important conservation implications for Bald Eagles by addressing issues related to variation in habitat quality within a continuous ecosystem and the determination of core breeding zones.