Comparison of Winter Habitats in Jamaica Used by American Redstarts
By Gregory Gough
As tropical forests are cut down, habitat for birds that nest in temperate regions, and migrate to overwinter in tropical areas, is lost. However, for some species, some agricultural habitats may provide adequate winter habitat.
The American redstart, a bird that nests in eastern North America, was studied in Jamaica on its wintering grounds. This small songbird inhabits a variety of wooded areas where it searches for its insect prey.
It was studied in 4 natural habitats: mangrove, coastal scrub, coastal palm, and dry limestone forest; and 2 agricultural habitats: citrus orchard and shade grown coffee plantation.
Redstarts were most common in mangrove, coastal scrub, and shade coffee. Coastal palm and citrus orchard supported lower numbers and the dry limestone forest was the least favored habitat.
So both the shade coffee plantation and citrus orchard provided winter habitat for the American redstart. Both these agricultural areas provide trees in which the redstarts forage.
This article summarizes the information in this publication:
Johnson, Matthew D., Sherry, Thomas W., Holmes, Richard T. and Marra, Peter P. 2006. Assessing Habitat Quality for a Migratory Songbird Wintering in Natural and Agricultural Habitats. Conservation Biology, 20(5): 1433-1444.
As tropical forests are cleared, a greater proportion of migratory songbirds are forced to winter in agricultural and disturbed habitats, which, if poorer in quality than natural forests, could contribute to population declines. We compared demographic indicators of habitat quality for a focal species, the American Redstart (Setophaga ruticilla), wintering in Jamaican citrus orchards and shade coffee plantations with those in four natural habitats: mangrove, coastal scrub, coastal palm, and dry limestone forests. Demographic measures of habitat quality included density, age and sex ratio, apparent survival, and changes in body mass. Measures of habitat quality for redstarts in citrus and coffee habitats were generally intermediate between the highest (mangrove) and lowest (dry limestone) measurements from natural habitats. The decline in mean body mass over the winter period was a strong predictor of annual survival rate among habitats, and we suggest that measures of body condition coupled with survival data provide the best measures of habitat quality for nonbreeding songbirds. Density, which is far easier to estimate, was correlated with these more labor-intensive measures, particularly in the late winter when food is likely most limiting. Thus, local density may be useful as an approximation of habitat quality for wintering migrant warblers. Ourfindings bolster those of previous studies based on bird abundance that suggest arboreal agricultural habitats in the tropics can be useful for the conservation of generalist, insectivorous birds, including many migratory passerines such as redstarts.
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