Greater Sage-Grouse (Centrocercus urophasianus) have declined in distribution and abundance in western North America over the past century. Depredation of nests and predation of chicks can be two of the most influential factors limiting their productivity. Prey species utilize antipredation behaviors, such as predator avoidance, to reduce the risk of predation. Birds in general balance the dual necessity of selecting cover to hide from visual and olfactory predators to enhance prospects of survival and reproductive success, which may also be achieved by selecting habitat with relatively fewer predators. We compared avian predator densities at Greater Sage-Grouse nests and brood locations with those at random locations within available sage-grouse habitat in Wyoming. This comparison allowed us to assess the species' ability to avoid avian predators during nesting and early brood rearing. During 2008–2010, we conducted 10-min point-count surveys at 218 nests, 249 brood locations from 83 broods, and 496 random locations. We found that random locations had higher densities of avian predators compared with nest and brood locations. Greater Sage-Grouse nested in areas where there were lower densities of Common Ravens (Corvus corax), Black-billed Magpies (Pica hudsonia), Golden Eagles (Aquila chrysaetos), and hawks (Buteo spp.) compared with random locations. Additionally, they selected brood-rearing locations with lower densities of those same avian predators and of American Kestrels (Falco sparverius), compared with random locations. By selecting nest and brood-rearing locations with lower avian predator densities, Greater Sage-Grouse may reduce the risk of nest depredation and predation on eggs, chicks, and hens.

Understanding the nature of social groups may help explain the genetic structure of populations. Recently, a finescale genetic structure was found in the Greater Snow Goose (Chen caerulescens atlantica) among adults captured in different brood-rearing sites. Such a structure requires assortative pairing among birds coming from the same brood-rearing site, a process that could be enhanced if individuals maintain stable associations over time. We verified whether stable groups persisted throughout the annual cycle of this migratory species. We used an 18-year data set of females marked on brood-rearing sites in the Arctic (n = 16,060) and recaptured on those sites or resighted on the breeding, staging, or wintering grounds in subsequent years. We used a probabilistic method to compare the number of associations observed with the number expected by chance alone. Our results provide no evidence that stable groups persist in flocks during migration or in winter among adult females. However, females marked at the same brood-rearing site had a greater probability of being found nesting together or of being recaptured together on the brood-rearing area in subsequent years than expected by chance. We suggest that the latter associations are more likely due to the fidelity of females to their nesting and brood-rearing site than a consequence of the formation of stable aggregations among individuals. Our results do not support the hypothesis that formation of stable groups is a mechanism that promotes assortative pairing by allowing individuals from the same brood-rearing area to remain together during the non-breeding season in Greater Snow Geese.

Comprendre la nature des groupes sociaux peut aider à expliquer la structure génétique des populations. Récemment, une structure génétique à petite échelle spatiale a été mise en évidence chez la Grande Oie des neiges (Chen caerulescens atlantica) parmi des adultes ayant été capturés sur différents sites d'élevage des jeunes. Une telle structure nécessite une préférence pour des individus assortis provenant du même site d'élevage lors du choix d'un partenaire, un processus qui pourrait être facilité si les individus maintiennent des associations stables dans le temps. Nous avons vérifié si des groupes stables persistent lors de la migration annuelle de cette espèce. Nous avons utilisé une base de données s' échelonnant sur 18 ans de femelles marquées sur les sites d'élevage dans l'Arctique (n = 16 060) et recapturées sur ces sites ou réobservées sur les sites de reproduction, de halte migratoire ou d'hivernage dans les années subséquentes. Nous avons utilisé une approche probabiliste pour comparer le nombre d'associations observées au nombre attendu dû au hasard seulement. Nos résultats démontrent aucune évidence que des groupes stables de femelles adultes persistent dans les volées durant la migration ou l'hivernage. Cependant, les femelles marquées sur le même site d'élevage avaient une plus grande probabilité d'être retrouvées nichant ensemble ou d'être recapturées ensembles sur les sites d'élevage les années subséquentes que ce qui aurait été attendu par hasard. Nous suggérons que ces associations sont probablement dues à une fidélité des femelles à leur site de nidification et d'élevage des jeunes plutôt que la conséquence de la formation d'agrégations stables entre les individus. Nos résultats ne supportent pas l'hypothèse que la formation de groupes stables soit un mécanisme facilitant le choix d'un partenaire assorti en permettant aux individus provenant du même site d'élevage de rester ensemble durant tout le cycle annuel chez la Grande Oie des neiges.

Multiple parasitism of host nests by generalist brood parasites reflects the decisions of laying females and may influence the development and behavior of parasitic young. We used microsatellite and mtDNA control-region haplotype data to examine the relatedness of Brown-headed Cowbird (Molothrus ater) offspring in multiply parasitized nests sampled from a heavily parasitized host community in northeastern Kansas. We also examined how host nest availability influenced the degree of multiple parasitism, and used community-wide parasitism data to explore whether female cowbirds were constrained in their laying decisions. Relatedness estimates for all suitable pairwise comparisons (n = 94 from 41 multiply parasitized nests) found that the mean likelihood than an individual cowbird in a multiply parasitized nest shared its nest with a full sibling was 40.4% (95% confidence interval: 28.4–52.4%), indicating that many cowbird offspring were reared with full siblings. Extensive community-wide parasitism data revealed that most cowbird offspring shared the nest with ≥1 other conspecific. Additionally, we found that the proportion of available host nests increased steeply at the start of the breeding season and remained high for most of the breeding season, but that the degree of multiple parasitism was unrelated to the number of new nests. We found evidence that laying decisions of female cowbirds were constrained, which suggests that heavy parasitism levels were due to a high degree of competition for host nests. This intense competition for host nests, in turn, results in cowbird offspring often competing with conspecifics in our population, including full siblings, for host parental care.

Many avian species exhibit a transition from biparental to uniparental care, but the reasons for this pattern are largely unknown. We examined the transition from biparental to paternal-only care in a small Arctic seabird, the Dovekie (Alle alle). We monitored colony attendance of males and females throughout the chick-rearing period in 2008–2010, investigating the sex ratio of breeders and following individually marked parents of both sexes in the colony at Magdalenefjorden (northwestern Spitsbergen). To understand reasons for the female's behavior, we also examined the birds' parental efforts and changes in chick body mass. We found that females fed the chicks less than males but provisioned the chick until very late in the chick-rearing period. Brood desertion occurred in 95% of nests and took place 3 days, 2 days, or 1 day prior to fledging (in 24%, 39%, and 69% of nests, respectively), on the 26th day of the chick's life, on average. Chicks experienced body-mass recession beginning, on average, on the 24th day of life (the recession assumed to be related to the female's desertion) and departed the colony, on average, on the 26th day of life. Contrary to other colonies, we did not find a significant bias of sex ratio in the birds provisioning at the end of the nesting period. The results undermine most general hypotheses explaining the causality of brood desertion. In fact, brood desertion in the Dovekie seems to be flexible and to depend on environmental conditions.

Nest predation is a major cause of reproductive failure for many birds; as a consequence, birds that can assess the abundance of predators and avoid nesting where they perceive predation risk to be high should be favored. For dabbling ducks, mammals are important predators on nests and incubating females. Many mammals use urine for marking territories. Because ducks may be able to detect mammalian urine either by ultraviolet light reflectance or by odor, we hypothesized that ducks may be able to assess the abundance of mammalian predators from their urine and thereby avoid nesting where mammals are abundant. We simulated increased predator abundance on experimental plots by using Red Fox (Vulpes vulpes) urine to make artificial scent marks and used water in a similar fashion on control plots. On 16 pairs of plots over 2 years, fewer ducks nested on experimental plots than on control plots (97 vs. 143 nests). These results suggest that birds can assess predator abundance and use the information to choose where to nest.

Large-scale monitoring of bird populations is often based on count data collected across spatial scales that may include multiple physiographic regions and habitat types. Monitoring at large spatial scales may require multiple survey platforms (e.g., from boats and land when monitoring coastal species) and multiple survey methods. It becomes especially important to explicitly account for detection probability when analyzing count data that have been collected using multiple survey platforms or methods. We evaluated a new analytical framework, N-mixture models, to estimate actual abundance while accounting for multiple detection biases. During May 2006, we made repeated counts of Black Oystercatchers (Haematopus bachmani) from boats in the Puget Sound area of Washington (n = 55 sites) and from land along the coast of Oregon (n = 56 sites). We used a Bayesian analysis of N-mixture models to (1) assess detection probability as a function of environmental and survey covariates and (2) estimate total Black Oystercatcher abundance during the breeding season in the two regions. Probability of detecting individuals during boat-based surveys was 0.75 (95% credible interval: 0.42–0.91) and was not influenced by tidal stage. Detection probability from surveys conducted on foot was 0.68 (0.39–0.90); the latter was not influenced by fog, wind, or number of observers but was ∼35% lower during rain. The estimated population size was 321 birds (262–511) in Washington and 311 (276–382) in Oregon. N-mixture models provide a flexible framework for modeling count data and covariates in large-scale bird monitoring programs designed to understand population change.

We show how the duration of primary replacement can be calculated from a knowledge of primary loss intervals, primary lengths, and primary growth rates. With this new method, we can now independently evaluate the reliability of regression or maximum likelihood estimators of molt duration in situations where recaptures are not available. Before, molting birds had to be recaptured and scored for molt at least twice in the same episode of molt to check the reliability of duration estimates based on samples of birds scored for molt a single time. This new method assumes only that feathers are lost in sequence. Unlike regression and likelihood estimators of molt duration, it requires neither that the same number of feathers are always replaced nor that molt is confined to a single season and reasonably synchronized across the population. Thus, it can be used to (1) estimate the duration of primary molts in species that molt and breed throughout the year, (2) estimate the time required to replace variable numbers of primaries, and (3) calculate start dates for molts that are initiated at various points in the primaries. We also show how to set confidence limits for these calculated estimates of molt duration. Finally, a variation of the method can be used to calculate where to sample feather material for measuring stable isotopes at evenly spaced time intervals through the primary replacement.

Responses of organisms to environments or to conspecifics may abruptly change once the organism has changed its state. For example, the expression of sexually selected signals often depends on the pairing status of the sender. A likely change in signaling routines at the point of pair formation should thus be taken into account when investigating a sexually selected trait like birdsong. However, female breeding behavior is elusive in many species, and the date of pair formation may be unknown. We developed a change-point model in a Bayesian context to analyze the seasonally changing singing activity in male Nightingales (Luscinia megarhynchos) for which the pairing status was assumed to be unknown. We used our change-point singing activity model to estimate the pairing status of the males as well as the dates of pair formation (i.e., the unobserved switches of states). We obtained results on pairing success and date of pair formation that were consistent with our data from mist netting and with the results of earlier studies. We also found that the peak in nocturnal and dawn singing activity was after the period of female arrival and was later in the season in unpaired males than in paired males. On the basis of our analyses, we argue that change-point models are powerful analytical tools for many fields of research and can be used whenever animals abruptly switch behavioral routines.

Climate change can cause mismatches between the breeding phenology and peak abundance of food resources of migratory species. Moreover, asynchronously changing climate regimes across their ranges may constrain the ability of migratory species to adapt to all the regimes they encounter. To understand the potential effect of asynchronous changes, I examined the influences of both large- and local-scale weather and climate on the timing of arrival of two disjunct breeding populations of Hudsonian Godwits (Limosa haemastica). I used arrival data from two study sites—Beluga River, Alaska, and Churchill, Manitoba—combined with 37 years of weather and climate data from both winter and stopover sites and the breeding grounds. The Alaskan population now arrives ∼9 days earlier than it did in the early 1970s, and the Churchill population arrives >10 days later. A model-selection process using linear regression models suggested that these divergent trends result from different suites of environmental factors affecting the timing of migration for the two populations. The cues used by the Alaskan population have remained reliable indicators of the timing of the onset of spring on their breeding grounds, but this is not the case for the Churchill population. Conflicting warming regimes in midcontinental North America cause the Churchill population to arrive later to their breeding grounds and limit their ability to properly time their breeding efforts. These results suggest that ecological and phenological limitations, not just evolutionary constraints, are critical to determining how populations respond to climate change.

Territorial social behavior of wintering Nearctic—Neotropic migrant songbirds places males and females in direct conflict over access to winter space and resources. Outcomes of this intersexual competition can vary by species and habitat, but information has been collected for only a small subset of migrant species. We investigated the available food resources, sex ratios, and body condition of territorial Bicknell's Thrushes (Catharus bicknelli) wintering in the Dominican Republic between 1999 and 2008 at two ecologically distinct wet-forest sites, one in high-elevation cloud forest and the other in mid-elevation rainforest. Arthropod abundance was greater in cloud forest habitat, which was occupied by proportionally more males, the larger-bodied sex (74% male). By contrast, both sexes occurred at parity in rainforest habitat (53% male), where soft-bodied fruit was the predominant dietary resource. Body condition of cloud forest males was comparable to that of rainforest males, but cloud forest females were in poorer body condition than rainforest females. Females at the cloud forest site may face a greater likelihood of agonistic interactions with larger-bodied males and the thermoregulatory demands of roosting in colder night temperatures (0–12^°C). We suggest that there are sex-specific advantages of wintering in these two habitats and that both are critical to supporting the full demographic structure of Bicknell's Thrush populations. Rainforest habitats, which are highly vulnerable to agricultural development in the Dominican Republic, may be particularly important to female survival during the winter period.

Recent changes in the timing of spring migration associated with climate change are occurring in hundreds of species of Northern Hemisphere birds. Much less is known about effects on autumn migration, especially for birds of prey. I studied simultaneous changes in spring and autumn phenology using data from 14 raptor species at two bird observatories on the shore of Lake Superior, North America. Median migration date advanced by 0.13 days·year^-1 in spring and was delayed by 0.23 days·year^-1 in autumn, with significant heterogeneity among species. Long-distance migrants were observed late in spring and early in autumn and showed less phenological change during autumn than short-distance migrants. The migratory period has become more extended, especially for short-distance migrants. Opposite responses during the two seasons had the effect of extending time spent to the north of the study area, by up to 30 days in some species since the early 1970s. These phenological shifts—potentially related to climate change— are causing dramatic changes in the annual cycle of North American raptors; whether these are beneficial or detrimental is unknown.

A new species of marabou, Leptoptilos lüi sp. nov., is described on the basis of a cranium, distal humerus, and proximal phalanx of the major digit, from the Middle Pleistocene Jinniushan locality, Liaoning Province of northeastern China. Fossil crania of the genus Leptoptilos are rare, and that of the new bird is distinct from the crania of its extant relatives. The forelimb elements are the largest and most robust among living and fossil species of Leptoptilos and are characterized by autapomorphic characters. Leptoptilos lüi, like the African Marabou Stork (L. crumeniferus), probably possessed a considerable flight capability and fed mainly on pieces of carrion torn from carcasses by other, sympatric large scavengers. The new stork aids in our understanding of the paleoecology and paleoenvironment of northeastern China in the Middle Pleistocene, helps us characterize the scavenger guild that fed on the Middle Pleistocene megafauna, and shows that the genus Leptoptilos, now restricted to the Old World tropics, extended into higher latitudes in the Middle Pleistocene.

Wild birds play a key role in the amplification and transmission of many of the arthropod-borne viruses (arboviruses). Determining the extent to which birds are affected by these viruses is critical in predicting the pathogens' spread or maintenance in vertebrate host populations. Little is known about how arboviruses affect amplifying hosts' fitness, especially in cases where these viruses infect nestling birds. Buggy Creek virus (BCRV; Togaviridae: Alphavirus) is an RNA arbovirus transmitted by the Swallow Bug (Oeciacus vicarius) to Cliff Swallows (Petrochelidon pyrrhonota) and House Sparrows (Passer domesticus) that have recently occupied Cliff Swallow nesting colonies. We examined fitness, as measured by fledging success, of House Sparrows occupying Cliff Swallow nesting colonies in western Nebraska. Most nestlings naturally infected by BCRV at 4–6 days of age died, and even older nestlings, when infected, showed fledging success of <40%. Whether ≥1 nestling in a brood was infected with BCRV was the most important determinant of nest success in this population. Colony sites with high BCRV prevalence had lower rates of nest success, and surviving broods at those sites were smaller. Although most infected nestling House Sparrows eventually die, they survive long enough to infect Swallow Bugs, and in this way they play a critical role in BCRV transmission. Frequent emigration of unexposed House Sparrows into these colonies and their renesting throughout the summer leads to these sites being perpetual foci for BCRV epizootics. Few other arboviruses are known to have such extreme effects on the fitness of their vertebrate hosts.

We examined heterozygosity at hypervariable microsatellite loci and blood parasite presence—absence in five populations of Golden-winged Warblers (Vermivora chrysoptera) that span the species' Canadian range. All populations were predominantly composed of genetically pure individuals, with small proportions of phenotypic and genetic hybrids. By comparing heterozygosity and infection status in concert, we tested whether more-heterozygous individuals have lower parasite prevalence, perhaps because they possess a more robust immune system. By considering the genetic status (pure vs. hybrid) of individuals in relation to infection by parasites and heterozygosity, we build on existing research that examines the effect of Blue-winged Warbler (V. cyanoptera) hybridization on Golden-winged Warbler populations. Finally, by looking at populations across the east—west range of the species, we could hypothesize what role geographic variation in vectors might play in population-level infection rates. We found no difference in infection probability between pure and hybrid individuals, but a greater frequency of infection in populations in the western portion of the range. Our results add to the growing evidence that hybrids in this system do not face postzygotic selection, and that Golden-winged Warblers breeding in the most northwestern extent of their range may face challenges that could impede their conservation. Ongoing work that compares reproductive success of Ontario and Manitoba populations is likely to add an important dimension to our findings and could further inform conservation efforts for the species.

Populations of Red Knots (Calidris canutus rufa) have declined an estimated 80% in the past 25 years. Declines are primarily attributed to dwindling food resources in Delaware Bay, their last migratory stopover before the breeding grounds. Red Knots wintering in Florida also decreased in numbers, prompting the need to estimate local vital rates to determine whether local factors contribute to declining trends. We estimated age-specific annual survival rates and compared them with estimates from populations of Red Knots wintering in South America using the Barker model. Adult annual survival rates between 2005 and 2010 averaged 0.89 ± 0.02 [SD]; range: 0.86–0.94) and were similar to estimates reported for Delaware Bay (0.87–0.92). Juvenile survival (0.95 ± 0.06 [SE]) and adult fidelity (0.81 ± 0.05 [SE]) were also high. However, juvenile survival did not include the period between fledging and arrival in Florida, a period of potentially high mortality. Similar adult survival rates suggested that there was no apparent survival cost for adults migrating to and from Florida compared with those migrating elsewhere. Factors that influence adult survival likely affect populations of C. c. rufa where they co-occur (e.g., breeding grounds, staging areas). Low year-to-year variation (CV = 2.24%) of adult survival suggests that other vital rates with higher variation (e.g., recruitment) may exert a stronger influence on population growth and partly account for the observed decline. Status projections require estimates of fecundity, year-round juvenile survival, and winter distribution in the United States.

Global climate cycles have been shown to influence demographic rates of birds at local scales, but few analyses have examined these effects at larger, regional scales. We examined the relationship of broad-scale climate indices to apparent survival of a subspecies of Swainson's Thrush (Catharus ustulatus) across a large portion of the subspecies' breeding range along the Pacific slope of North America. We developed 69 a priori Cormack-Jolly-Seber models to examine effects of El Niño—Southern Oscillation (ENSO), North Atlantic Oscillation, Pacific Decadal Oscillation, latitude, region, and residency status on survival. The most parsimonious model included an ENSO effect, a regional effect, and a residency effect on survival. The ENSO had a positive effect on survival probability, and the effect was consistent across the entire portion of the breeding range examined. Additional analyses of a posteriori models provided strong support for an effect of dry-season precipitation along the spring migration route in western Mexico on annual survival. Our results suggest that survival of this Neotropical migrant is strongly influenced by ENSO-related weather changes during one or more periods of its annual cycle. Because many western Neotropical migrants migrate through and winter in the same general geographic area as Swainson's Thrushes, it is possible that other such species are similarly influenced by ENSO. If, as some climate models predict, annual variation in ENSO increases, Swainson's Thrush may suffer greater variation in annual survival. Directly associating climate with key demographic parameters provides a powerful approach to predicting a species' response to climate change.

Understanding how animals will adapt to climate change requires understanding how climate variables influence their biology year round, and how events in different seasons interact. Migratory birds may be especially vulnerable because of the wide range of geographic areas that they depend on throughout the annual cycle. We examined the potential effects of non-breeding season climate change on the breeding biology of Kirtland's Warbler (Setophaga kirtlandii, formerly Dendroica kirtlandii), an endangered songbird that breeds in the Northern Lower Peninsula of Michigan and winters in the Bahamas. Our objectives were to determine whether spring arrival dates on the breeding grounds correlate with late winter rainfall in non-breeding areas and whether this has consequences for reproductive success. We used data on spring arrival dates and number of fledglings per year, sampling many individuals across multiple years, to show that males arrive on breeding grounds later following drier winters. There was a strong male age * rainfall interaction, which indicates that first-time breeders were much more sensitive to changes in rainfall than experienced adults. Regardless of age, however, drier winters and delayed arrival and nest initiation were significantly associated with fewer offspring fledged. These results are important because the Caribbean region is currently experiencing a significant drying trend, and climate change models predict that the severity of this drought will continue to increase. Any resulting adjustments to the timing of migration could constrain spring arrival dates and limit reproductive success for the endangered Kirtland's Warbler, as well as other Neotropical migrants wintering in the Caribbean.

Comprender cómo los animales se adaptan al cambio climático requiere entender cómo las variables climáticas afectan su biología a lo largo del año, y cómo interactúan los eventos sucedidos en diferentes temporadas. Las aves migratorias pueden ser especialmente vulnerables dado el amplio espectro de áreas geográficas de las que ellas dependen a lo largo del ciclo anual. Examinamos los efectos potenciales del cambio climático en las temporadas no reproductivas sobre la biología reproductiva de Setophaga kirtlandii (antes Dendroica kirtlandii), un ave canora amenazadaque se reproduce en el norte de la peninsula inferior de Michigan y pasa el invierno en las Bahamas. Nuestros objetivos fueron determinar si las fechas de llegada a las áreas de reproducción en primavera se correlacionan con la precipitación del final del invierno en la áreas no reproductivas, y si lo anterior tiene consecuencias sobre el éxito reproductivo. Usamos datos de las fechas de llegada en primavera y el número de volantones por año, muestreando múltiples individuos a lo largo de múltiples años, y logramos demostrar que los machos llegan a las áreas de reproducción más tarde luego de inviernos más secos. Hubo una interaccián fuerte entre la edad de los machos y la precipitacián, de modo que los que se reproducían por primera vez fueron mucho más sensibles a los cambios en la precipitación que los adultos más experimentados. Sin embargo, independientemente de la edad, los inviernos más secos y la llegada e iniciación tardía de la anidación estuvieron significativamente asociados con un menor número de crías emplumadas. Estos resultados son importantes porque la región Caribe actualmente está experimentando una tendencia hacia la aridez y los modelos de cambio climático predicen que la severidad de la sequía continuará incrementándose. Cualquier desajuste en la sincronización de la migración que se produzca como consecuencia de lo anterior podría restringir las fechas de arribo en la primavera y limitar el éxito reproductivo de S. kirtlandii, así como de otros migrantes neotropicales que pasan el invierno en el Caribe.

Although changes in the mean arrival and breeding dates of some species are expected in response to climate change, other species may respond to direct or indirect climate effects by modifying the duration of their breeding period. We used a 20-year database for two closely related species that breed in sympatry in Europe, the short-distance migrant Dalmatian Pelican (Pelecanus crispus) and the long-distance migrant Great White Pelican (P. onocrotalus), to test for changes in breeding phenology over the past two decades. Median laying dates of the species covaried over time, indicating that the same or similar environmental factors probably influenced both species at their breeding sites. However, direct climate effects were revealed only for the short-distance migrant species, which showed a rapid advancement in its median laying dates (1.4 days year^-1). This shift was associated with (1) an increase in population size and (2) weather variation following warmer and wetter winters. Earlier breeding was associated with enhanced survival of juvenile Dalmatian Pelicans, especially during hot and wet years. The Great White Pelican exhibited no advancement in its median laying date, but it significantly reduced the duration of its laying period (1.7 days year^-1) by advancing the latest laying date. Furthermore, the response of the Great White Pelican was related only to factors of population size. Further analyses of breeders' interactions within and between species might help to identify possible indirect effects of environmental changes on both species and should be further considered for their future conservation.

Restoration and maintenance of barrier islands to preserve structural integrity and protect against erosional forces is a common goal of coastal protection. An assessment of restored barrier islands for their suitability as wildlife habitat is crucial for improvement of restoration methods and conservation of barrier-island-dwelling species, especially ground-nesting waterbirds. During the 2008 and 2009 breeding periods, we conducted a quantitative assessment of colonial waterbird use of the Isles Dernieres Barrier Island Refuge (IDBIR), Louisiana, which has experienced several restoration projects since the early 1990s, to understand the breeding ecology of two terns in the genus Thalasseus and investigated why some restored areas have not been colonized. Our objectives were to determine hatching success of the two species, identify important habitat characteristics for their reproduction and colony formation, and evaluate the success of past restoration efforts in providing suitable nesting habitat. Habitat characteristics were important for hatching success, including spatial attributes of nest sites and substrate composition. Discriminant function analysis revealed that suitable habitat for colony formation was available at some inactive restored areas, but the majority of inactive areas were unsuitable. The paucity of nesting activity at potentially suitable restored areas may be attributable to the greater activity of mammalian predators that we detected at inactive areas than at active colony sites. Management of restored barrier islands for specific waterbird habitat requirements, creation of new islands containing suitable ground-nesting habitat, and appropriate control of mammalian predators are critical factors for effective waterbird conservation and ecosystem function in these disturbance-prone regions.

Diverse patterns of parental care, including uniparental care by either the male or the female, provide excellent opportunities to investigate how variation in social traits is maintained in wild populations. Coexistence of different parental strategies within the same population is expected when they exhibit similar cost-benefit ratios. We investigated one of the most diverse avian breeding systems and compared parental behavior and reproductive output between nests that are uniparentally cared for by male or female Eurasian Penduline Tits (Remiz pendulinus). In this small passerine bird, full care (incubation and brood care) is provided by the male only (7–18% of nests) or the female only (48–65% of nests). Additionally, a third of all nests are deserted by both parents as a result of intense sexual conflict over care. We show that parental effort is similar between male and female parents, and they achieve similar offspring survival after controlling for clutch-size differences. Females care for larger clutches than males (5.7 ± 0.1 [SE] and 3.5 ± 0.2 eggs, respectively), and they produce more nestlings (3.6 ± 0.2 and 2.4 ± 0.3 nestlings, respectively), although this difference is not significant at fledging of the chicks (3.1 ± 0.2 and 2.4 ± 0.3 young, respectively). Therefore, sex difference in care does not explain the bias toward female-only care in Eurasian Penduline Tits. We propose that the differential benefits of desertion and/or the differential costs of care for males and females facilitate the existence of both uniparental care types in the population.