Matthew W. Reudink

Non-breeding season events influence sexual selection in a long-distance migratory bird

The study of sexual selection has traditionally focused on events and behaviours immediately surrounding copulation. In this study, we examine whether carry-over effects from the non-breeding season can influence the process of sexual selection in a long-distance migratory bird, the American redstart (Setophaga ruticilla). Previous work on American redstarts demonstrated that overwintering in a high-quality habitat influences spring departure dates from the wintering grounds, advances arrival dates on the breeding grounds and increases apparent reproductive success. We show that the mixed-mating strategy of American redstarts compounds the benefits of overwintering in high-quality winter habitats. Males arriving to breed in Canada from high-quality winter habitats arrive earlier than males from poor-quality habitats, resulting in a lower probability of paternity loss, a higher probability of achieving polygyny and ultimately higher realized reproductive success. Such results suggest that the process of sexual selection may be influenced by events interacting throughout the annual cycle.

Hydrogen isotopic variation in migratory bird tissues of known origin: implications for geographic assignment

Continent-wide variation in hydrogen isotopic composition of precipitation is incorporated into animal diets, providing an intrinsic marker of geographic location at the time of tissue growth. Feathers from migratory birds are now frequently analyzed for stable-hydrogen isotopes (δD) to estimate the location of individuals during a preceding molt. Using known-origin birds, we tested several assumptions associated with this emerging technique. We examined hydrogen isotopic variation as a function of age, sex, feather type and the timing of molt in a marked population of American redstarts (Setophaga ruticilla) breeding in southeastern Ontario. We measured δD in feathers and blood from individuals that bred or hatched at our study site during the year in which those tissues were grown. Juvenile tissues from 5- to 10-day-old birds had more negative δD values than those from adults, which most likely reflected age-related differences in diet. Within adults, primary feathers had more negative δD values than contour feathers. The mean δD value in adult primary feathers was relatively consistent among years and with the value expected for our study population. However, among-individual variation in δD corresponded to an estimated latitudinal range of 6–8° (650–900xa0km). We conclude that feathers sampled from recently hatched juveniles may not provide a reliable estimate of expected local isotopic signatures for comparison with adult feathers of unknown origin. Furthermore, we urge researchers to use caution when using δD values in feathers to infer geographic origin, and suggest that the best approach is to assign individuals to broad geographic zones within a species’ potential molting range.

Historical pesticide applications coincided with an altered diet of aerially foraging insectivorous chimney swifts

Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected, but the cause remains unknown partly because of a dearth of long-term monitoring data on avian diets. Chimney swifts (Chaetura pelagica) are a model aerial insectivore to fill such information gaps because their roosting behaviour makes them easy to sample in large numbers over long time periods. We report a 48-year-long (1944–1992) dietary record for the chimney swift, determined from a well-preserved deposit of guano and egested insect remains in Ontario (Canada). This unique archive of palaeo-environmental data reflecting past chimney swift diets revealed a steep rise in dichlorodiphenyltrichloroethane (DDT) and metabolites, which were correlated with a decrease in Coleoptera remains and an increase in Hemiptera remains, indicating a significant change in chimney swift prey. We argue that DDT applications decimated Coleoptera populations and dramatically altered insect community structure by the 1960s, triggering nutritional consequences for swifts and other aerial insectivores.

Evidence for Introgression in the Endangered Sonora Tiger Salamander, Ambystoma tigrinum stebbinsi (Lowe)

Abstract Introduction of nonnative species and consequent genetic introgression of native taxa is a primary conservation concern, particularly for endangered species. Our ongoing molecular study of the endangered Sonora Tiger Salamander, Ambystoma tigrinum stebbinsi (Lowe), has uncovered evidence of introgression by the Barred Tiger Salamander, Ambystoma tigrinum mavortium. We conducted both mitochondrial DNA sequencing and analyses of nine microsatellite loci to (1) evaluate the distinctiveness of A. t. stebbinsi from the two other tiger salamander subspecies in Arizona; and (2) test for introgression in A. t. stebbinsi. Two mitochondrial haplotypes were found. One was undescribed for tiger salamanders, and the other was identical to that found in nearby A. t. mavortium. Microsatellite analyses, including assignment tests, diagnostic alleles, and high genetic distances, supported distinctness of A. t. stebbinsi. Thirty-nine animals that were putatively A. t. stebbinsi had mtDNA haplotypes identical to those in A. t. mavortium. These 39 individuals were distributed among six ponds, where a total of 73 individuals were sampled for microsatellites and considered “unknowns” because of the shared haplotype with A. t. mavortium. Assignment tests and diagnostic alleles of microsatellite data indicated that five of these 73 individuals may be hybrids of A. t. mavortium and A. t. stebbinsi. Some salamanders within the geographic range of A. t. stebbinsi were morphologically similar to A. t. mavortium or intermediate between the two subspecies. Our results suggest that introgression from introduced A. t. mavortium may be altering the gene pool of A. t. stebbinsi, thereby raising concerns about continued management of this endangered species.

Mitochondrial Evidence for Panmixia despite Perceived Barriers to Gene Flow in a Widely Distributed Waterbird

We examined the mitochondrial genetic structure of American white pelicans (Pelecanus erythrorhynchos) to: 1) verify or refute whether American white pelicans are panmictic and 2) understand if any lack of genetic structure is the result of contemporary processes or historical phenomena. Sequence analysis of mitochondrial DNA control region haplotypes of 367 individuals from 19 colonies located across their North American range revealed a lack of population genetic or phylogeographic structure. This lack of structure was unexpected because: 1) Major geographic barriers such as the North American Continental Divide are thought to limit dispersal; 2) Differences in migratory behavior are expected to promote population differentiation; and 3) Many widespread North American migratory bird species show historic patterns of differentiation resulting from having inhabited multiple glacial refugia. Further, high haplotype diversity and many rare haplotypes are maintained across the species distribution, despite frequent local extinctions and recolonizations that are expected to decrease diversity. Our findings suggest that American white pelicans have a high effective population size and low natal philopatry. We suggest that the rangewide panmixia we observed in American white pelicans is due to high historical and contemporary gene flow, enabled by high mobility and a lack of effective physical or behavioral barriers.

Carotenoid-based Male Plumage Predicts Parental Investment in the American Redstart

Abstract We examined whether male plumage coloration signals parental quality in the American Redstart (Setophaga ruticilla), a highly ornamented, migratory warbler. We measured the relationship between both adult male arrival date and phenotype (morphology, melanin- and carotenoid-based plumage), and parental care levels of both parents. Males with brighter flank feathers made more visits to the nest and spent more time at the nest, consistent with the ‘good-parent hypothesis’. Female parental care (number of visits) was negatively correlated with intensity of red of her mates tail feathers and positively associated with her mates parental effort. These data indicate offspring of brighter males receive more care from both parents. Our results suggest carotenoid-based plumage traits of male American Redstarts may have an important role in intersexual signaling, and add to our understanding of the evolution of multiple ornaments.

STRUCTURE AND DYNAMICS OF THE HYBRID ZONE BETWEEN BLACK-CAPPED CHICKADEE (POECILE ATRICAPILLUS) AND CAROLINA CHICKADEE (P. CAROLINENSIS) IN SOUTHEASTERN PENNSYLVANIA

Abstract Analysis of the structure and stability of a hybrid zone can serve as a starting point for examining mechanisms that influence spatial and evolutionary relationships between species. Recent studies of the hybrid zone between Black-capped Chickadee (Poecile atricapillus) and Carolina Chickadee (P. carolinensis) have suggested that genetic introgression is limited to a narrow zone, while also reinforcing the conclusion that the line of contact between these parapatrically distributed species is now shifting northward. We investigated the structure, position, and recent movement of the chickadee hybrid zone in southeastern Pennsylvania. Using selectively neutral microsatellite DNA markers, along with mitochondrial DNA haplotypes, we documented large differences in genetic composition among three populations ≤65 km apart where we sampled large numbers of breeding residents during 1998–2003. Genetic results indicate that the three sites support a population of Carolina Chickadees (Great Marsh), a population in which most individuals exhibit evidence of hybridization (Nolde Forest), and a population comprising mostly Black-capped Chickadees but with evidence of hybridization now taking place (Hawk Mountain). The patterns within the Nolde Forest population suggest that selection against hybrids may not be as strong as has been concluded from studies in other parts of the chickadee hybrid zone. Comparison of mitochondrial and nuclear genotypes between samples collected ≈15 years apart suggest that the northern edge of the hybrid zone shifted by ≈20 km over this interval, with hybridization now occurring as far north as the Kittatinny Ridge and beyond, where only Black-capped Chickadee genotypes were previously detectable. Our data and historical accounts suggest that the hybrid zone, now ≈50 km wide, may have become wider while also shifting northward. These results support the hypothesis that Carolina Chickadees enjoy a selective advantage during hybridization with Black-capped Chickadees, but both the proximate mechanisms and ultimate causes remain to be investigated. Structure et dynamique de la zone dhybridation entre Poecile atricapillus et P. carolinensis dans le sud-est de la Pennsylvanie

Inter-annual variation in American redstart (Setophaga ruticilla) plumage colour is associated with rainfall and temperature during moult: an 11-year study.

Carotenoid-based colouration plays an important role in sexual signaling in animals as an honest indicator of individual quality during mate choice and competitive interactions. However, few studies have examined how natural variation in weather conditions influences inter-annual variation in the expression of ornamentation, potentially through affecting the dietary availability of carotenoids. In this study, we examine variation in the expression of carotenoid-based plumage colouration in relation to temperature and rainfall during the pre-moulting and moulting period over 11xa0years in a population of American redstarts, Setophaga ruticilla, breeding in eastern Canada. We used reflectance spectrometry of tail feathers collected from male and female redstarts to relate feather colour with weather conditions the previous breeding season during the months over which redstarts are likely to moult (June–September). At a population level, birds expressed feathers with higher red chroma and lower brightness in years following high July rainfall and low August temperature. The pattern was stronger in males, but was generally consistent across ages and sexes. Analyses of feathers from repeatedly captured birds indicated that the above patterns could be explained by individual change in feather colour. We suggest that higher rainfall during the moulting period may increase insect abundance and the availability of dietary carotenoids. This is among the first studies to show effects of weather conditions on a sexual signalling trait, which may have important consequences for sexual selection, mate choice, and the reliability of putative signals.

Color expression in experimentally regrown feathers of an overwintering migratory bird: implications for signaling and seasonal interactions

Plumage coloration in birds plays a critical role in communication and can be under selection throughout the annual cycle as a sexual and social signal. However, for migratory birds, little is known about the acquisition and maintenance of colorful plumage during the nonbreeding period. Winter habitat could influence the quality of colorful plumage, ultimately carrying over to influence sexual selection and social interactions during the breeding period. In addition to the annual growth of colorful feathers, feather loss from agonistic interactions or predator avoidance could require birds to replace colorful feathers in winter or experience plumage degradation. We hypothesized that conditions on the wintering grounds of migratory birds influence the quality of colorful plumage. We predicted that the quality of American redstart (Setophaga ruticilla) tail feathers regrown after experimental removal in Jamaica, West Indies, would be positively associated with habitat quality, body condition, and testosterone. Both yearling (SY) and adult (ASY) males regrew feathers with lower red chroma, suggesting reduced carotenoid content. While we did not observe a change in hue in ASY males, SY males shifted from yellow to orange plumage resembling experimentally regrown ASY feathers. We did not observe any effects of habitat, testosterone, or mass change. Our results demonstrate that redstarts are limited in their ability to adequately replace colorful plumage, regardless of habitat, in winter. Thus, feather loss on the nonbreeding grounds can affect social signals, potentially negatively carrying over to the breeding period.

Moult migration in Bullock's orioles (Icterus bullockii) confirmed by geolocators and stable isotope analysis

AbstractIn contrast to the majority of migratory songbirds in North America, which moult on or near their breeding grounds, the Bullock’s oriole (Icterus bullockii) is reported to stop during fall migration to moult en route to the wintering grounds. These birds seem to take advantage of food resources during the Mexican monsoon season in the Southwestern USA and Northwestern Mexico. We studied a population of Bullock’s orioles at the northern limit of their breeding range in Kamloops, British Columbia, Canada, using a combination of light-level geolocators and stable hydrogen isotope analysis. We found evidence that supports the existence of moult migration in this species, with geolocators indicating that all birds appeared to stay in the Mexican monsoon region for moult in an extended stopover period during fall migration. Feathers were isotopically enriched with deuterium compared to predicted breeding isotope values and were significantly more negative than winter-grown claws, confirming that moult occurred somewhere between the breeding and wintering grounds. Stable isotope data were consistent with complete prebasic stopover moult in adults and complete contour feather and variable tail feather moult in first-year orioles. Our results confirm that this northern population of Bullock’s orioles employs a moult migration strategy and highlight the usefulness of combining geolocator and stable isotope studies.ZusammenfassungBestätigung des Mauserzugs beim Bullocktrupial(Icterus bullockii)mit Hilfe von Geolokatoren und stabiler Isotopen Im Gegensatz zu den meisten ziehenden Singvögeln Nordamerikas, die in oder in der Nähe ihres Brutgebiets mausern, wird über den Bullocktrupial (Icterus bullockii) berichtet, dass er auf dem Herbstzug ins Überwinterungsgebiet unterwegs einen Mauserstopp einlegt. Diese Vögel nutzen anscheinend Nahrungsressourcen im Südwesten der USA und im Nordwesten Mexikos während der mexikanischen Monsunsaison. Wir haben eine Population des Bullocktrupials am nördlichen Rand seines Brutgebiets in Kamloops in Britisch-Kolumbien, Kanada, mit Hilfe einer Kombination von Helldunkelgeolokatoren und stabiler Wasserstoffisotopenanalyse untersucht. Wir fanden Hinweise, welche die Existenz von Mauserzug bei dieser Art unterstützen; Geolokatoren zeigten an, dass alle Vögel zur Mauser offenbar in der mexikanischen Monsunregion blieben und dafür einen längeren Stopp auf dem Herbstzug einlegten. Die Federn waren im Vergleich zu den vorhergesagten Brutgebiet-Isotopenwerten mit Deuterium-Isotopen angereichert und signifikant negativer als im Winter gewachsene Krallen, was bestätigt, dass die Mauser irgendwo zwischen Brut- und Überwinterungsgebiet erfolgte. Die stabilen Isotopdaten standen mit einer kompletten Postnuptialmauser im Rastgebiet bei Adulttieren und einer kompletten Konturfeder- und variablen Schwanzfedermauser bei einjährigen Tieren im Einklang. Unsere Ergebnisse bestätigen, dass diese nördliche Population von Bullocktrupialen einen Mauserzug machen, und unterstreichen die Nützlichkeit einer Kombination von Geolokatorstudien und stabilen Isotopenanalysen.