Southern Warblers Cross Gulf First

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 publication:

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.

View abstract

Each spring, millions of songbirds migrate across the Gulf of Mexico on their way to breeding sites in North America. Data from radar and migration monitoring stations have revealed broad patterns in the spatial and temporal course of trans-Gulf migration. Unfortunately, we have limited information on where these birds have previously spent the winter and where they are migrating to breed. Here we measure stable-hydrogen isotopes in feathers (dDf ) to infer the breeding latitude of five species of songbirds ! hooded warblers Wilsonia citrina, American redstarts Setophaga ruticilla, black-andwhite warblers Mniotilta varia, ovenbirds Seiurus aurocapilla, and northern waterthrushes S. noveboracensis ! that were captured at a stopover site along the coast of southwestern Louisiana in spring 2004. Values of dDf across all species ranged from "163 to "35! (n#212), and within most species the range was consistent with the latitudinal extent of known breeding sites in central and eastern North America. Individuals that arrived first along the northern Gulf coast had dDf values indicative of southerly breeding sites in hooded warblers, American redstarts, black-and-white warblers, and ovenbirds, but no relationship was found between passage timing and dDf for northern waterthrushes. Our findings suggest that spring passage is often timed to coincide with the emergence of suitable conditions on breeding areas, with southern breeding birds migrating first.

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