Summary
Many species of birds exhibit brilliant ornamental plumage, yet most research on the function and evolution of plumage has been confined to the breeding season. In the American redstart Setophaga ruticilla, a long‐distance Neotropical‐Nearctic migratory bird, the acquisition of a winter territory in high‐quality habitat advances spring departure and subsequent arrival on breeding areas, and increases reproductive success and annual survival. Here, we show that males holding winter territories in high‐quality, black mangrove habitats in Jamaica have brighter yellow‐orange tail feathers than males occupying territories in poor‐quality second‐growth scrub habitats. Moreover, males arriving on the breeding grounds from higher‐quality winter habitats (inferred by stable‐carbon isotopes) also had brighter tail feathers. Because behavioral dominance plays an important role in the acquisition of winter territories, plumage brightness may also be related to fighting ability and the acquisition and maintenance of territories in high‐quality habitat. These results highlight the need for further research on the relationships between plumage coloration, behavior, and the ecology of over‐wintering migratory birds.
Methodology
Study species
Our study species was the American redstart, a small (7-8 g) and widespread Nearctic-Neotropical migratory songbird. American redstarts breed throughout much of North America and winter throughout the Caribbean, Mexico, and parts of Central and northern South America (Sherry and Holmes 1997). Recent work suggests that American redstarts over-wintering in the Caribbean breed in the northeastern United States and southeastern Canada, including Ontario (Norris et al. 2006). American redstarts are sexually dimorphic; males exhibit delayed plumage maturation, with highly variable plumage coloration both within and between age classes. Individuals undergo a single pre-basic molt at the end of the breeding season and retain those feathers through the following breeding season (Sherry and Holmes 1997). In their first winter (and subsequent breeding season), males are greenish-gray with yellow carotenoid-based patches on their wings, tail, and flanks. These males lack bibs entirely, but some individuals adventitiously molt in small patches of black feathers on the breast, back and head during winter. After their first breeding season, males molt into their definitive plumage: black upperparts and head with a white belly, salmonorange carotenoid-based patches on the wings, tail and flanks and a black bib (Sherry and Holmes 1997). Studies from the breeding grounds suggest that bib size is related to breeding-season performance (Perrault et al. 1997), though the function of the carotenoid-based patches has not yet been investigated.
Study sites
Over-wintering American redstarts were captured in highquality (black mangrove) and low-quality (second-growth scrub) habitats from Dec.-March 2002-2006 at Font Hill Nature Preserve, Westmoreland Parish, Jamaica, West Indies (18° 02' N, 77° 57' W; see Marra 2000). Sample numbers varied yearly based on accessibility to different habitats and the duration of our stay. Work on the breeding grounds was conducted May-July 2006 at the Queen’s Univ. Biological Station, Chaffey’s Lock, Ontario, Canada (44° 34' N, 76° 19' W).
Tissue sampling
All birds were captured in mist nets either through passive blanket netting or using song playbacks accompanied by a decoy, and banded with a single US Fish and Wildlife Service or Canadian Wildlife Service band and 2-3 color bands for individual identification. On the breeding grounds in May 2006, birds were captured within 5 d of arrival and 2-3 mm of the central claw from each foot was collected; claw samples in Jamaica were obtained in March 2006. For all birds, we recorded wing chord (mm) and plucked a single tail feather (R3) for color and stablehydrogen isotope analysis.