Kevin J. Kardynal

A Continent-Wide Migratory Divide in North American Breeding Barn Swallows (Hirundo rustica).

Populations of most North American aerial insectivores have undergone steep population declines over the past 40 years but the relative importance of factors operating on breeding, wintering, or stopover sites remains unknown. We used archival light-level geolocators to track the phenology, movements and winter locations of barn swallows (Hirdundo rustica; n = 27) from populations across North America to determine their migratory connectivity. We identified an east-west continental migratory divide for barn swallows with birds from western regions (Washington State, USA (n = 8) and Saskatchewan, Canada (n = 5)) traveling shorter distances to wintering areas ranging from Oregon to northern Colombia than eastern populations (Ontario (n = 3) and New Brunswick (n = 10), Canada) which wintered in South America south of the Amazon basin. A single swallow from a stable population in Alabama shared a similar migration route to eastern barn swallows but wintered farther north in northeast Brazil indicating a potential leap frog pattern migratory among eastern birds. Six of 9 (67%) birds from the two eastern populations and Alabama underwent a loop migration west of fall migration routes including around the Gulf of Mexico travelling a mean of 2,224 km and 722 km longer on spring migration, respectively. Longer migration distances, including the requirement to cross the Caribbean Sea and Gulf of Mexico and subsequent shorter sedentary wintering periods, may exacerbate declines for populations breeding in northeastern North America.

Western Veeries use an eastern shortest-distance pathway: New insights to migration routes and phenology using light-level geolocators

ABSTRACT We investigated movements of a western population of Veeries (Catharus fuscescens) breeding in the Okanagan region of British Columbia, Canada, in 2013–2014 using light-level geolocators. We tracked 9 individuals and incorporated a state-space Kalman filter model approach to estimate movement parameters. During migration, Veeries traversed the Rocky Mountains, Great Plains, Gulf of Mexico, and Caribbean Sea with stopovers generally closer to the shorter orthodromic (great circle) route than a loxodromic (straight line) route between breeding and first wintering grounds, particularly on fall migration. Birds initially settled in the south-central portion of the Amazon basin in Brazil at sites that were 666 ± 299 km apart, suggesting low migratory connectivity. Intra-tropical movements were observed for 8 of 9 (88.9%) birds, with second wintering sites an average of 1,447 ± 472 km to the northwest (initial bearing x̄ = 316 ± 16°). Veeries typically followed a pattern of loop migration at the Gulf of Mexico, with more birds using the Yucatan Peninsula to stop and reorient toward destinations on spring migration (n = 7) vs. fall migration (n = 2). Western Veeries follow a presumed ancestral (eastern) migration route, but this route is also the shortest (great circle) route between breeding and wintering grounds, even though this route was only ~100 km shorter than the straight line route. Eight Veeries (88.9%) underwent a post-breeding, pre-migratory movement up to 628 km (x̄ = 263 ± 152 km) away from breeding territories, possibly to molt. We encourage researchers utilizing light-level geolocators to apply similar state-space modeling approaches to reduce the influence of observers and erroneous location estimates on analysis and interpretation of geolocator data.

An isotope (δ34S) filter and geolocator results constrain a dual feather isoscape (δ2H, δ13C) to identify the wintering grounds of North American Barn Swallows

ABSTRACT The discovery of spatial patterns in naturally occurring isotopes (e.g., δ2H, δ13C) at continental scales has been tremendously important in providing a method to infer potential breeding and wintering origins of migratory animals through assignment to tissue-specific isoscapes. Single-isotope (i.e. δ2H) assignments of birds to molting origins in South America have been limited by the lack of strong spatial gradients in precipitation δ2H there. We integrated an mvnpdf (multivariate normal probability density function) approach using δ2H and δ13C values in tail feathers to determine wintering origins of adult Barn Swallows (Hirundo rustica) breeding in eastern Canada (n = 208). Spatial assignments were conducted using precipitation (δ2H) and theoretical plant-based (δ13C) isoscapes for South America calibrated for feathers of Nearctic–Neotropical migrant songbirds. We also measured feather δ34S values of Barn Swallows equipped with geolocators (n = 9) and of a larger group of Barn Swallows (n = 121) of unknown molt origin to assess the possibility of using this isotope to identify birds molting in coastal habitats and for which the terrestrial δ2H isoscapes would potentially be invalid. We constrained the mvnpdf assignment to areas generally south of the Amazon basin, based on data retrieved from Barn Swallows fitted with archival light-level geolocators from Ontario (n = 3) and New Brunswick (n = 11), Canada, which showed consistent overwintering fidelity to south-central South America. The majority of birds from our breeding populations were assigned to south-central Brazil. Results from the δ34S analysis indicate that a threshold of 11‰ may be appropriate to constrain the use of terrestrial δ2H isoscapes in South America. Our results refine the toolbox available to examine migratory connectivity in species that molt on their South American wintering grounds and underline the value of using multiple proxies for assignments of animals to spatial origin.

Are Boreal Riparian Bird Communities Unique? Contrasting Riparian and Upland Bird Assemblages in the Boreal Plain of Western Canada

Riparian ecotones in arid regions often contain unique species and have higher species richness and abundance relative to upland habitats making them of higher conservation priority than other habitats. However, such differences in species richness and abundance may not be apparent in more mesic regions. We compared species frequency of occurrence and abundance, richness and turnover of bird assemblages in two aquatic ecotone types with those in nearby interior upland forests in the boreal forest of Alberta, Canada. Riparian edge habitats had higher species richness and more species with significant indicator values than lowland forest edge or interior upland forest and the greatest differences in bird community composition were between riparian edge and upland interio habitats. Species turnover was highest in riparian habitats attributable to the presence of rare species or higher spatial and structural heterogeneity of those systems. When contrasting the upland forested area adjacent to the waterbody versus a similar sized area in the upland forest interior, riparian areas still contained higher richness but had fewer indicator species. We suggest that riparian areas and the adjacent shoreline forest contribute considerably to the regional richness of bird communities in the boreal forest and management policies should reflect this characteristic.

Shorebird hunting in Barbados: Using stable isotopes to link the harvest at a migratory stopover site with sources of production

ABSTRACT Understanding spatial connectivity of long-distance migrants is important for effective management and conservation of both game and nongame species. Hunting of Nearctic-breeding shorebirds occurs in the Caribbean and northern South America; however, the origins of harvested individuals are generally unknown. We used stable hydrogen isotopes (δ2H) in feathers of juvenile shorebirds to infer the origins of birds harvested at 2 sites in Barbados using probabilistic assignments based on a terrestrial–freshwater δ2H isoscape. We used tissue δ13C and δ15N values to filter individuals that had derived nutrients from marine sources. Natal origins of juvenile American Golden-Plover (Pluvialis dominica), Stilt Sandpiper (Calidris himantopus), Short-billed Dowitcher (Limnodromus griseus), and Lesser Yellowlegs (Tringa flavipes) were predicted to be mainly from the eastern parts of their breeding ranges in eastern Canada, with American Golden-Plover, Stilt Sandpiper, and Short-billed Dowitcher also having high potential areas of origin in parts of Alaska, USA. Results from our study should help to modify prior estimates of sustainable harvest levels for these species. We identify sources of uncertainty in determining shorebird origins using stable isotopes, including a lack of shorebird-specific calibration equations and the apparent lack of an appropriate tissue for breeding ground assignment for adults.

Use of natural and anthropogenic land cover by wintering Yellow Warblers: The influence of sex and breeding origin

ABSTRACT Sex, age, body size, and breeding origin can influence the nonbreeding distribution of long-distance migratory birds. At continental scales, differential migration can lead to segregation of various classes or populations among different regions. At local scales, class segregation can occur among habitats of differing qualities, often due to dominance interactions related to sex, age, and body size. Conversion of natural habitats to agriculture in the Neotropics is leading to more birds wintering in modified landscapes. We examined how sex, age, size, and breeding origin influenced the use of 3 land cover types (riparian gallery forest, coastal lagoon vegetation, and agriculture) by wintering migratory Yellow Warblers (Setophaga petechia) in western Mexico. Between 2012 and 2014, we used point counts in 6 study sites to estimate Yellow Warbler densities, and we captured, sexed, and aged 205 birds to characterize individuals using each land cover type. Breeding origin was inferred using stable hydrogen isotope ratios (δ2H) in feathers. Contrary to our expectations, Yellow Warbler densities were highest in agricultural sites (5.6 ± 0.7 SE birds ha−1) and lower in sites with natural land cover (riparian gallery forest: 3.6 ± 0.5 birds ha−1; scrub mangrove: 2.0 ± 0.4 birds ha−1). The Yellow Warbler population wintering in our study sites was male-biased (64%), and the use of sites with natural vs. agricultural land cover was not influenced by sex, age, or size of individuals, suggesting that competitive interactions are not limiting access to sites with different land cover. We found that females from more northerly breeding or natal origins were more likely to winter in sites with natural land cover, while females from more southerly origins were more likely to use agricultural sites. Our results suggest that localized population declines could occur via survival differences or carryover effects if condition or subsequent reproductive success differs between birds wintering in sites with natural vs. agricultural land cover.

Estimating densities of terrestrial wildlife using passive acoustic recordings: A pragmatic approach using paired human observations

The use of passive using acoustic monitoring is a rapidly growing field in terrestrial ecology, particularly in ornithology. Much recent work has focused on using recording technologies for large-scale occupancy monitoring, while local scale studies have focused on acoustic localization for density estimation. Density estimation offers numerous advantages for answering key conservation questions but may seem impractical to employ at national or continental scales using current acoustic localization techniques. Here, we describe how paired sampling can be used in conjunction with generalized linear (GLM) or generalized linear mixed models (GLMM) to estimate correction factors (δ) to derive density estimates from single acoustic recorders, provided that paired human observers conduct distance estimation. Thus, our approach provides an alternative to more complicated and expensive methods. We discuss the advantages and disadvantages of our approach and highlight the context in which we see various existing or emerging acoustic density estimation methods being used in the terrestrial environment, given the nature and scale of the ecological question(s) being asked.

Inferring origins of migrating insects using isoscapes: a case study using the true armyworm, Mythimna unipuncta, in North America: Origins of dispersing and migrating insects

1. Many important insect pests undertake seasonal migrations at continental scales in response to changes in resource quality and availability. The frequency and timing of these events could be influenced by the impact of climate change on the suitability of the different sites exploited throughout the year, yet, in many cases, little is known about the origin of seasonal populations, as tracking insect movements is extremely challenging due to their small body size.