An exploration of migratory connectivity of the Rufous Hummingbird (Selasphorus rufus), using feather deuterium

Rufous Hummingbirds (Selasphorus rufus) undertake an annual migration between breeding grounds in western North America and wintering grounds in south-central Mexico, with a small wintering population on the Gulf Coast of the USA. However, little is known about the pattern of connectivity between the breeding and wintering grounds for this species. The aim of the study was to explore migratory connectivity in S. rufus, using feather deuterium (δ ² H). Selasphorus rufus molt on the wintering grounds, so newly-grown feathers of adult birds carry an isotopic signature characteristic of the overwintering area. Tail feathers were collected from 229 adult birds from six breeding sites located in British Columbia and Alberta, Canada, and Alaska, USA. The δ ² H signatures of feathers from birds at each site were used for geospatial allocation of wintering range onto one amount-weighted δ ² H precipitation isoscape (North America) and one shallow groundwater δ ² H isoscape (Mexico), using reduced major axis regression. The relationship between feather δ ² H (δ ² H f ) and amount-weighted precipitation δ ² H (δ ² H ₚ ) in S. rufus was tighter than that found in other avian taxa to date, and is comparable to that reported previously for the Ruby-throated Hummingbird (Archilochus colubris). At three of the breeding sites, males showed significantly higher δ ² H f values compared to females, suggesting possible allopatric separation (with an altitudinal component) on the wintering grounds. This pattern did not hold for the two most easterly breeding sites. For female birds at the three western breeding sites, the predicted wintering area lies at higher altitude in Mexico than for birds from the breeding sites further east. For male birds, there was a less marked difference in δ ² H f between most of the breeding sites, although it is likely that birds from the western breeding sites share overwintering range, and that those from the eastern breeding sites overwinter at lower elevations.