Millions of songbirds fly across the Gulf of Mexico each spring on the way from their wintering grounds to their breeding grounds. Scientists captured five species of warblers (see below) at a migration stopover site in southwestern Louisiana to find out where they were going.
Pictured from left to right: black-and-white warbler, American redstart, ovenbird, hooded warbler, and northern waterthrush
Scientists collected a tail feather from each bird and analyzed its hydrogen content. The birds grew their tail feathers on their breeding grounds the previous year and hydrogen varies by latitude—birds nesting further north have different hydrogen isotopes than birds breeding in the south.
Each of these warblers has a fairly wide breeding range spanning most of Canada and the northern United States, but individual birds usually return to the same territory year after year.
Birds were captured from late March through early May. Those captured earliest, for all species except the northern waterthrush, were birds that nested in the southern part of their range.
The birds appear to be timing their migration so that they arrive on the breeding grounds as early possible, but also when harsh weather has passed and food is available.
This article summarizes the information in this scientific paper:
Langin, K. M., Marra, Peter P., Nemeth, Z., Moore, F. R., Kyser, T. K. and Ratcliffe, L. M. 2009. Breeding latitude and timing of spring migration in songbirds crossing the Gulf of Mexico. Journal of Avian Biology, 40(3): 309-316.
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