Migratory connectivity describes linkages between breeding and non-breeding areas. An ongoing challenge is tracking avian species between breeding and non-breeding areas and hence estimating migratory connectivity and seasonal survival. Collaborative color-ringing projects between researchers and citizen scientists provide opportunities for tracking the annual movements of avian species. Our study describes seasonal survival and migratory connectivity using data from more than 4,600 individuals with over 51,000 observations, predominantly collected by citizen scientists. Our study focuses on the Eurasian Oystercatcher (Haematopus ostralegus), a species that has experienced a substantial and ongoing decline in recent decades. Multiple threats have been described, and given that these threats vary in space and time, there is an urgent need to estimate demographic rates at the appropriate spatio-temporal scale. We performed a seasonal multi-state (5 geographical areas within The Netherlands) live- and dead-recoveries analysis under varying model structures to account for biological and data complexity. Coastal breeding populations were largely sedentary, while inland breeding populations were migratory and the direction of migration varied among areas, which has not been described previously. Our results indicated that survival was lower during winter than summer and that survival was lower in inland areas compared with coastal areas. A concerning result was that seasonal survival of individuals over-wintering in the Wadden Sea, an internationally important site for over-wintering shorebirds, appeared to decline during the study period. We discuss the outcomes of our study, and how citizen science was integral for conducting this study. Our findings identify how the demographic rates of the oystercatcher vary in space and time, knowledge that is vital for generating hypotheses and prioritizing future research into the causes of decline.

Hosts of avian brood parasites, such as cuckoos, are duped into taking care of a foreign chick and this has led to the evolution of host defenses, such as egg rejection. However, many host species are not egg rejecters and it has been suggested that poor illumination inside closed nests may constrain the evolution of this defense. In this study, we experimentally increased the light inside the dome nests of Yellow-Rumped Thornbills, the main host of the Shining Bronze-Cuckoo. Our results show that rejection events did not increase significantly when nests were brighter, although there is a possibility that rejection mistakes could decrease. Moreover, we found that natural light levels inside dome nests were highly variable, and in many cases as high as those in cup-nesting species with high rejection rates. This evidence suggests that rapid changes in nest illumination do not alter rejection behavior.

Aerial insectivores are highly mobile predators that feed on diverse prey items that have highly variable distributions. As such, investigating the diet, prey selection and prey availability of aerial insectivores can be challenging. In this study, we used an integrated DNA barcoding method to investigate the diet and food supply of Barn Swallows, an aerial insectivore whose North American population has declined over the past 40 yr. We tested the hypotheses that Barn Swallows are generalist insectivores when provisioning their young and select prey based on size. We predicted that the diets of nestlings would contain a range of insect taxa but would be biased towards large prey items and that the diet of nestlings would change as prey availability changed. We collected insects using Malaise traps at 10 breeding sites and identified specimens using standard DNA barcoding. The sequences from these insect specimens were used to create a custom reference database of prey species and their relative sizes for our study area. We identified insect prey items from nestling fecal samples by using high-throughput DNA sequencing and comparing the sequences to our custom reference database. Barn Swallows fed nestlings prey items from 130 families representing 13 orders but showed selection for larger prey items that were predominantly from 7 dipteran families. Nestling diet varied both within and between breeding seasons as well as between breeding sites. This dietary flexibility suggests that Barn Swallows are able to adjust their provisioning to changing prey availability on the breeding grounds when feeding their nestlings. Our study demonstrates the utility of custom reference databases for linking the abundance and size of insect prey in the habitat with prey consumed when employing molecular methods for dietary analysis.

Duetting has been intensively studied, but we still have little consensus about its fitness consequences. Some studies suggest that duetting functions in acoustic mate guarding to prevent cuckoldry (acoustic paternity guarding hypothesis), whereas other studies argue that duetting is a cooperative behavior to defend common resources (territory defense hypothesis). We tested these 2 hypotheses by investigating the relationships among song traits, extra-pair paternity, territory quality and reproductive success in the Rufous Hornero (Furnarius rufus), a Neotropical, socially monogamous bird. We found a low rate of extra-pair paternity (3.33% of 120 offspring and 6.52% of 46 broods), which suggests that acoustic paternity guarding is probably not a primary function of duetting behavior in this species. Female song output was positively correlated with territory quality, measured as the availability of territory foraging patches. The number of young that survived post-fledging was positively correlated with duet duration, but not with territory features. Our results support the territory defense hypothesis, suggesting that female song in duets might be used in the defense of food resources within territories. Our study provides the first evidence that song traits correlate with both territory features and reproductive success in a duetting species.

The scarcity of free-standing water sources is a key determinant of animal and plant community structure in arid environments, and an understanding of the extent to which particular species use surface water is vital for modeling the effects of climate change on desert avifauna. We investigated interspecific variation in the use of artificial water sources among birds in the Kalahari Desert, South Africa, by (i) observations at waterholes and (ii) tracing spatial water-use patterns during summer by isotopically labeled water sources and blood sampling. More than 50% of the avian community (primarily insectivores and omnivores) were not observed to drink. The majority (53%) of species drinking at waterholes were granivorous, and their use of surface water was best predicted by their relative abundance in the community. Species representing the remaining dietary guilds drank significantly more on hot days. Blood samples revealed that only 11 of 42 species (mostly granivores and a few omnivores) showed evidence of drinking at a waterhole with enriched deuterium values; on average, in the latter birds, water from the enriched waterhole accounted for ∼38% of their body water pool. These findings illustrate that 2 methods employed in this study provide different, but complementary data on the relative importance of a water source for an avian community. Although our results suggest that most avian species are independent of surface water, drinking patterns on the hottest days during our study period suggest that free-standing water might become more important for some of the non-drinking species under hotter climatic conditions.

The study of avian movement has detailed a spectrum of strategies for the timing and use of sites throughout the annual cycle, from near randomness to complete consistency. New tracking devices now permit the repeated tracking of individual animals throughout the annual cycle, detailing previously unappreciated levels of variation within migratory systems. Godwits (genus Limosa) have featured prominently in studies of avian migration, but information derived from repeated tracking of individuals is limited. The Marbled Godwit subspecies Limosa fedoa beringiae breeds on the central Alaska Peninsula, and little is known about basic aspects of its migration ecology, including the repeatability with which this population times its annual migratory movements or uses migratory and nonbreeding sites. To address these questions, we equipped 9 Marbled Godwits breeding at a site near Ugashik, Alaska, with solar-powered satellite transmitters. We tracked individuals from July, 2008 to October, 2015 and obtained repeat migratory tracks from 5 of these birds. Individuals exhibited high fidelity to breeding, nonbreeding, and migratory stopover sites across years, but in contrast to congeners that conduct consistently timed, long, nonstop migrations, beringiae Marbled Godwits exhibited low levels of individual- or population-level repeatability in the timing of migratory movements. Their relatively short migrations may enable the integration of local environmental cues, potentially facilitating individual flexibility in the timing of annual migratory movements. Curiously, if local cues ultimately drive the timing of Marbled Godwit migratory movements, the population's relatively constrained distribution during both the breeding and nonbreeding season should serve to synchronize birds if they are responding to similar cues. That our sample of Marbled Godwits nonetheless exhibited within- and between-year variation in the timing of their migratory movements suggests a complex integration of annually variable internal and external cues.

Researchers studying the evolution of animal communication often ask what generates and maintains signal complexity, but they define and measure complexity in different ways. If different metrics are not concordant, then studies using them are probably not comparable. In this study, we asked whether 7 metrics of bird song complexity vary in tandem among individuals of a single species, the Rock Wren (Salpinctes obsoletus). The included metrics were chosen because they are regularly used by researchers in the field to test hypotheses within the literature. Results indicated that none of the metrics positively correlated with any others, suggesting that bird songs are not under general selective pressures favoring increased complexity across multiple features. If metrics of signal complexity are not correlated, then care should be taken when designing analyses and comparing results. Researchers should always clearly define the “complexity” under investigation and verify that it has significance to the study species. Contradictory outcomes among existing research into signal “complexity” may result from the fact that this single word is used to represent multiple independent traits.

While social mate choice is an obvious point where sexual selection acts on males, cryptic selection can occur based on how much females invest in a male's offspring. I tested 4 hypotheses about the relationship between female investment and social mate attractiveness by manipulating a sexually selected trait, white tail feathers (“tail white”), in male Dark-eyed Juncos (Junco hyemalis thurberi): (1) the differential allocation hypothesis predicts that females optimize lifetime reproductive success by maximizing parental investment in the offspring of ornamented mates and minimizing investment when mated to less attractive males; (2) instead of positive differential allocation, females could show negative differential allocation by investing more in less attractive males to compensate for their lower quality; (3) female care could also be influenced directly by paternal investment, in particular what appears to be positive differential allocation could be compensation for reduced care by attractive males; or (4) females could reduce care when paired with socially attractive males that are “good parents”. To evaluate these hypotheses, I examined the impact of tail white manipulation on clutch size, female incubation and brooding, and female and male provisioning. Females did not differentially allocate in relation to social mate attractiveness, nor were females responsive to patterns of male investment, even although artificially attractive males provisioned offspring significantly more than did controls. Naturally bright males, who were also the largest males, did not provision at higher rates, highlighting the need to experimentally separate the role of specific traits from other correlated factors. Tail white-manipulated males were involved in rare cases of polygyny and at times were actively guarded by their mates. Together, these results suggest that tail white influences reproductive behaviors in this junco population, but because of the potential for extrapair paternity, additional data are needed to accurately investigate the trait's role in female investment.

The Great White Heron (GWH) has an all-white plumage and occurs in the Gulf of Mexico and Caribbean. Described originally as Ardea occidentalis, it is now considered a subspecies of Great Blue Heron (GBH; A. herodias). GWH and GBH meet in Florida Bay at the southern tip of Florida, providing the opportunity to evaluate their interaction and species status. To this end, we examined size variation and mate choice across their contact zone and genetic variation range-wide. Measurements of 7 morphological characters indicate trends, but not a significant difference, in size between GBH and GWH in southern Florida. GBH and GWH nest mainly in different places (mainland vs. islands) and at different peak times. In Florida Bay, mixed pairs occur, but white-white and blue-blue pairs are more common than in a randomly mating population. Assessing mating, however, is complicated because most, if not all, nesting blue birds are of mixed parentage. Microsatellite DNA analysis indicates that white and blue herons in Florida Bay and the outer Keys (outside Florida Bay) form a group distinct from blue forms on Florida Peninsula and elsewhere in North America. However, some gene flow occurs from white herons on the outer Keys to white and blue herons in Florida Bay, and from blue herons in Florida Bay to GBH on the Florida Peninsula. GWH alleles occur in all North American populations, but whether this is from gene flow or incomplete lineage sorting is unknown. Deciding GWH's species status is difficult. GWH and GBH meet in an ecotone where some gene flow occurs, but behavior and habitat largely isolate them. We argue in favor of splitting GWH from GBH. Regardless of how it is ultimately classified, the GWH's small population needs to be actively managed as an isolate in an extremely vulnerable environment.

Host-parasite relationships between Western Burrowing Owls (Athene cunicularia hypugaea) and the fleas (Pulex irritans, Siphonaptera: Pulicidae) they harbor were studied to understand the extent to which migratory Burrowing Owls translocated fleas from wintering grounds to breeding grounds. This has implications for host-parasite relationships in Burrowing Owls and also potentially for the dynamics of plague, as Burrowing Owl distributions overlap plague foci, owls inhabit fossorial mammal colonies where epizootic outbreaks of plague occur, and owls may harbor species of flea that are competent plague vectors. We used hydrogen stable isotope analysis to help elucidate geographic origins of fleas collected from adults and nestlings in 2 migratory populations of Burrowing Owls in Idaho and Oregon, USA. For adults, we posited that bird-mediated dispersal would impart flea isotopic compositions representative of southern latitudes and be similar to owl toenail tissue recently grown on wintering grounds, but they would differ from contour feathers presumably grown on breeding grounds the previous year. We assumed nestling feathers and toenails would have isotopic compositions representative of the breeding grounds. We analyzed contour feathers and toenails from adults collected shortly after they arrived in breeding grounds following spring migration and from nestlings later in the breeding season, to which we compared isotopic compositions in fleas collected from individuals of both age classes. Fleas on nestlings in both populations had isotopic compositions that did not differ from nestling feathers and toenails, suggesting that nestling fleas had breeding ground origins. Fleas on adults in one population (Oregon) had breeding ground isotopic signatures, as flea compositions did not differ from nestling feathers or toenails. Adult owls in Idaho had fleas that similarly did not express a wintering ground signature, but they were enriched in the heavy isotope (deuterium) relative to nestling feathers and toenails. Therefore, we discuss the possibility that adult owls in Idaho acquired fleas at migratory stopover sites. While the latter indicates that Burrowing Owls have the potential to disperse fleas, there was no evidence of continent-wide movement of fleas by owls from wintering grounds to breeding grounds.

Bird song is the primary animal model system for cultural evolution. Longitudinal studies of bird song across many generations can provide insights into patterns and mechanisms of change in socially transmitted traits. In this study, we conducted a comparative analysis of songs of the House Finch (Haemorhous mexicanus) across an interval of 37 years (in 1975 and in 2012). Recordings from both years were collected in western Long Island, New York, which is thought to be the initial site of introduction of the House Finch around 1940 from the West Coast. Song types experienced a complete turnover during this period, although half of the syllable types were represented in both samples. Song length, frequency bandwidth and several other spectrographic features were the same in both years, and no structural features predicted recurrence of individual syllables. Consistent with the fact that our study population expanded substantially following a cultural founder effect, song and syllable sharing and similarity between individuals were lower in 2012 than in 1975, reflecting an increase in song diversity at the population level. However, in the more recent sample individual songs had fewer syllables, and were sung with less sequence stereotypy across renditions than in the earlier sample. Syllable prevalence in 2012 was associated both with complexity (as gauged by frequency excursion) and increased minimum frequency. Thus, over nearly 4 decades, Eastern House Finch songs remained structurally similar at the whole-song level, diversified between individuals, but became simpler and less consistent within an individual.