Abstract Every year, millions of raptors migrate between their breeding areas in North America and their nonbreeding areas in Central and South America. Many investigations have demonstrated that weather plays a significant, yet complex role in the timing of bird migration at northern localities that, in turn, shapes their seasonal migration phenology. However, very little information is available for the Neotropical region. Here, we analyzed the relationship between local weather variables (wind-related components, humidity, and atmospheric pressure) and the intra- and inter-annual migration patterns of 8 raptor species with different migration ecologies. Our dataset spans between 23–26 years and was obtained at a raptor migration monitoring site at Mexico’s Gulf coastal plain, a well-known, globally important migration hotspot. Perhaps due to the often erratic and pulsed daily variation in migration phenology each year, classical analytical approaches do not consider quantifications of intra-annual variation. To address this, we devised a new method based on a finite approximation to the second derivative of the counts (roughness) to analyze the role of weather drivers in the patterns of daily counts. Additionally, we analyzed the inter-annual variation in migration timing, subtracting the mean number of individuals across all years for each day (deviations from the mean). Although we found significant differences in roughness across days, we observed a subtle association between weather and roughness in migration counts, regardless of the species’ flight strategy (such as thermal soaring and flapping). Only tailwind affected the intra-annual migration, although the models had a low explanatory power (marginal R2 ≤ 0.17). Similarly, we found inter-annual effects of tailwind and sidewind, depending on the type of migrant (long- and short-distance), but the models exhibited high variation and low explanatory power (marginal R2 ≤ 0.18). Moreover, the lagged effect of weather variables does not improve the variance explained by weather variables at any of the two timescales evaluated. The low association between migrant counts and weather calls for future research at larger spatial and temporal scales, as well as on assessing the cumulative effect of weather along raptor migration routes.

2-week hospitalization in June.

Journal Article 2023 AOS Elliott Coues Award to Gregory F. Ball and Jacques Balthazart Get access Marty Leonard, Marty Leonard Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada Corresponding author: mleonard@dal.ca Search for other works by this author on: Oxford Academic Google Scholar Mark Hauber, Mark Hauber Department of Animal Biology, University of Illinois, Urbana, Illinois, USA https://orcid.org/0000-0003-2014-4928 Search for other works by this author on: Oxford Academic Google Scholar Helen F James, Helen F James Division of Birds, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA https://orcid.org/0000-0002-2495-6133 Search for other works by this author on: Oxford Academic Google Scholar Tony D Williams, Tony D Williams Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada Search for other works by this author on: Oxford Academic Google Scholar Karen Wiebe Karen Wiebe Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada https://orcid.org/0000-0002-3148-8278 Search for other works by this author on: Oxford Academic Google Scholar Ornithology, Volume 140, Issue 4, 5 October 2023, ukad040, https://doi.org/10.1093/ornithology/ukad040 Published: 29 August 2023

Abstract Understanding the functional significance of bird sounds can provide valuable insight into the behavior and how birds use habitat. We show that the Common Nighthawk (Chordeiles minor) wing-boom display is a territorial signal associated with the nest location that can be used to identify territorial habitat use. In other words, the Common Nighthawk wing-boom display can be considered analogous to song due to its potential function in territoriality. We captured, tagged, and tracked 21 male Common Nighthawks in northeastern Alberta to confirm the functional significance of the wing-boom display and describe Common Nighthawk territoriality. Mean wing-boom use density (hereafter “area”) size was 10.2 ha (SD = 11.7 ha). We found minimal overlap in the wing-boom area (5 of 15 neighboring male pairs, 0.2–4.5% overlap), suggesting the wing-boom display represents an exclusive territory. Comparison of wing-boom locations and random points within the wing-boom area confirmed that male Common Nighthawks select areas near the nest to perform wing-boom displays. There was high wing-boom area overlap for the same individual between years. Differences between years reflected shifts in nest location, suggesting that the wing-boom display is a good indicator of the nest location and territory. Future Common Nighthawk surveys should record the type of acoustic signal observed to differentiate territorial habitat use from other functions. Many taxa that produce non-vocal sounds as part of breeding displays could similarly benefit from a functional understanding to provide insight into habitat use.

Abstract Using the patterns of fault bars in their primaries, we studied the mode of primary replacement in non-molting Lesser Sandhill Cranes (Antigone c. canadensis) salvaged from hunters in southwestern Saskatchewan. About 80% of their primaries are used for 2 yr and 20% for 3 yr. Primaries are replaced during the breeding season and are lost in synchronous blocks representing about half the primaries, suggesting that most adults probably can fly weakly during flight feather replacement. Cranes are large, aggressive birds, and this interesting, and undescribed mode of flight feather replacement seems adapted to the ability of adult cranes to defend their precocial chicks from predators. Strikingly, juvenile Sandhill Cranes showed no fault marks in their primaries, suggesting that their parents’ ability to protect them shields them from the fright of predator attacks, which, in most birds, causes fault bars to be more prevalent and strongly expressed in juveniles than adults. Adults show interesting variation in the number of primaries replaced annually, which seems likely related to whether or not they are caring for chicks. Further, single primaries may or may not be replaced preferentially, suggesting sensitivity to feather function. Evaluating these observations must await field studies of molting adults.

Abstract Migratory shorebirds (Charadrii) show a strong dichotomy in their breeding and wintering strategies: Arctic-breeding species typically spend the wintering season in marine habitats, while more southerly breeding species tend to do so in freshwater habitats where pathogens and parasites, particularly vector-borne blood parasites, are generally more abundant. Thus, it has been hypothesized that the former group may reduce their investment in immunity, but experimental data supporting this hypothesis are lacking. Moreover, whether this contrasting habitat selection can shape investments in immunocompetence among populations within a species is uncertain. We experimentally tested the hypothesis that there is a significant association between habitat occupancy and the strength of a pro-inflammatory immune response in the Dunlin (Calidris alpina), a widely distributed long-distance migratory shorebird that breeds in (sub-)arctic areas and winters mainly, but not exclusively, in coastal habitats. Overwintering Dunlins occupying inland freshwater and marine habitats at a similar latitude were captured and acclimated under identical conditions in outdoor aviaries. After an acclimation period, they were challenged with phytohemagglutinin to assess the pro-inflammatory immune response and its associated energetic costs, measured by basal metabolic rate (BMR) and body mass changes. We found that freshwater Dunlins exhibited a higher (63%) pro-inflammatory immune response than marine Dunlins. Although this difference did not involve significant BMR changes, the time course of body mass response differed between freshwater and marine individuals. Our findings point to the existence of different pro-inflammatory immune responses and body mass adjustments associated with the wintering habitat. These intraspecific differences are likely due to population adaptation rather than phenotypic plasticity, where not only disease risk but also physiological adaptations to different salinity levels could play an important role.

Abstract Hybrids with different combinations of traits can be used to identify genomic regions that underlie phenotypic characters important to species identity and recognition. Here, we explore links between genomic and plumage variation in Blue-winged Warbler x Golden-winged Warbler (Vermivora cyanoptera x V. chrysoptera) hybrids, which have traditionally been categorized into 2 discrete types. “Lawrence’s” hybrids are yellow overall, similar to Blue-winged Warblers, but exhibit the black throat patch and face mask of Golden-winged Warblers. “Brewster’s” hybrids are similar to Golden-winged Warblers, but lack the black throat patch and face mask, and sometimes have yellow on their underparts. Previous studies hypothesized that (1) first generation hybrids are of the Brewster’s type and can be distinguished by the amount of yellow on their underparts, and that (2) the throat patch/mask phenotype is consistent with Mendelian inheritance and controlled by variation in a locus near the Agouti-signaling protein (ASIP) gene. We addressed these hypotheses using whole genome re-sequencing of parental and hybrid individuals. We found that Brewster’s hybrids had genomic hybrid index scores indicating this phenotype can arise by majority ancestry from either parental species, that their plumage varied in levels of carotenoid pigmentation, and individuals captured in multiple years grew consistently less yellow over time. Variation in carotenoid pigmentation showed little relationship with genomic hybrid index score and is thus inconsistent with previous hypotheses that first generation hybrids can be distinguished by the amount of yellow in their plumage. Our results also confirm that variation near ASIP underlies the throat patch phenotype, which we refined to an ~10–15 Kb region upstream of the coding sequence. Overall, our results support the notion that traditional categorization of hybrids as either Lawrence’s or Brewster’s oversimplifies continuous variation in carotenoid pigmentation, and its inferred underlying genetic basis, and is based primarily on one discrete trait, which is the throat patch/mask phenotype.