Long-distance Dispersal Patterns of Male Cerulean Warblers (Dendroica cerulea) Measured by Stable-hydrogen Isotopes

Abstract

ABSTRACT. Despite the fundamental role played by long-distance dispersal in population dynamics, the mechanisms promoting or inhibiting dispersal by migratory songbirds are poorly understood. We used stable-hydrogen isotopes (δD) to evaluate several hypotheses related to long-distance dispersal in the Cerulean Warbler (Dendroica cerulea), a migratory songbird at the center of considerable conservation attention. Feather samples were collected from 103 males throughout the breeding range. We assumed feathers were molted in late summer on the breeding grounds and thus δD values provided an estimate of breeding or hatching location for the previous year. We used a likelihood-based assignment test to estimate the origin of birds the previous year and derived expected δD values for the entire Cerulean Warbler breeding range from precipitation-based maps. Using Bayes' Rule, we also incorporated a prior probability of breeding origin based on estimated rates of site fidelity and survival between breeding seasons. We found that long-distance breeding dispersal by adult male Cerulean Warblers was a fairly common occurrence with 20 of 71 (28.2%) individuals originating from a region other than the one they were sampled in. Surprisingly, long-distance natal dispersal was uncommon; only three of 32 (9.4%) second-year birds were estimated to have hatched in a region outside their capture region. Young males may be using a form of post-fledging prospecting or conspecific attraction when selecting their first breeding habitats. Populations on the breeding range periphery, such as Ontario and Tennessee, tended to receive fewer longdistance dispersers than did other regions but produced more dispersing individuals than did core regions, suggesting that these areas could act as important sources for other regions. The tendency of a region to produce dispersing individuals was not significantly related to its relative abundance, implying that population abundance is not a good indicator of population health for this species. Range-wide variation in long-distance dispersal patterns may contribute to variation in sensitivity to habitat loss and fragmentation, further complicating conservation and management efforts for the Cerulean Warbler.RÉSUMÉ. En dépit du fait que la dispersion sur de longues distances joue un rôle fondamental dans la dynamique des populations, les mécanismes qui la favorisent ou la freinent sont peu connus chez les passereaux migrateurs. Nous avons utilisé des isotopes stables d'hydrogène (δD) pour tester plusieurs hypothèses en rapport avec la dispersion sur de longues distances de la Paruline azurée, un passereau dont la conservation fait l'objet d'une grande attention. Des échantillons de plumes ont été récoltés sur 103 mâles dans l'ensemble de l'aire de reproduction de l'espèce. Nous présumons que la mue de ces plumes s'est produite à la fin de l'été sur les sites de reproduction et que les valeurs δD fournissent, par conséquent, une estimation du lieu de reproduction ou d'éclosion de l'année précédente. No...

Minimal Genetic Structure in the Cerulean Warbler Despite Evidence for Ecological Differentiation among Populations

“…For conservation purposes, to help delineate appropriate management units, it is important to investigate whether birds breeding in geographically isolated areas are genetically distinct. A study of the Cerulean Warbler's isotopic signatures yielded estimates of long-distance dispersal that were large (28.2% among breeding males, 9.4% among natal-year birds), suggesting that regions far enough apart to be isotopically different readily exchange genes (Girvan et al 2007). However, birds in the northern and southern portions of the range differ morphologically (Jones et al 2005) and may travel to different wintering grounds (Girvan et al 2007).…”

“…A study of the Cerulean Warbler's isotopic signatures yielded estimates of long-distance dispersal that were large (28.2% among breeding males, 9.4% among natal-year birds), suggesting that regions far enough apart to be isotopically different readily exchange genes (Girvan et al 2007). However, birds in the northern and southern portions of the range differ morphologically (Jones et al 2005) and may travel to different wintering grounds (Girvan et al 2007). Specifically, body size varies according to Bergmann's rule (Mayr 1956, Jones et al 2005, and deuterium/hydrogen ratios (ôD) suggest that Cerulean Warblers breeding north of Tennessee winter in northern South America (Venezuela, Colombia, and Ecuador), whereas birds from Tennessee winter farther south, in Peru and Bolivia (Girvan et al 2007).…”

Searching for a breeding population of Swinhoe’s Storm-petrel at Selvagem Grande, NE Atlantic, with a molecular characterization of occurring birds and relationships within the Hydrobatinae

“…It is particularly important in colonial species that occupy highly fragmented habitats, such as oceanic islands, and show strong site fidelity, which will slow down the rate of founder events (Matthiopoulos et al 2005). The factors promoting long-distance dispersal in avian species are still poorly understood, but are thought to be related to the characteristics of populations, such as their age structure, demography and abundance (Girvan et al 2007). The known breeding distribution of the procellariiform Swinhoe's Storm-petrel Oceanodroma monorhis includes islands off Japan, South Korea, Russia and China (Sato et al 2010).…”

Whither Natural History in Conservation Research?

“…Similarly, technological developments often permit new insights into the basic natural history of species. For example, analysis of the chemical composition of various tissues (Girvan et al 2007, Fraser et al 2008 or the use of light-level geolocators (e.g., Stutchbury et al 2009) can yield critical data on movements by individuals. However, regardless of how new insights arise, we still need to justify the need for specific natural history information depending on each particular conservation context, rather than collecting any and all natural history that could be potentially relevant to conservation.…”

“…De façon similaire, les avancées technologiques permettent souvent de faire de nouvelles découvertes au sujet de l'histoire naturelle des espèces. Par exemple, l'analyse de la composition chimique de différents tissus (Girvan et al 2007, Fraser et al 2008) ou l'utilisation de photomètres géolocalisateurs (p. ex. Stutchbury et al 2009) peuvent fournir des données essentielles sur les déplacements d'individus.…”