Sexual Differences in Wilson Warbler Migration

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[edit] Author(s)

• Otahal, C. D.

[edit] Journal

Journal of Field Ornithology 66.1 (1995): 60-69.

[edit] Keywords

juncos junco-hyemalis spring migration geographic-variation fat deposition stopover parulinae ratio

[edit] Abstract

Mist-netting was conducted in riparian habitat near the southern end of San Francisco Bay, California during the spring and fall migratory periods of Wilson's Warblers (Wilsonia pusilla) in 1987-1991. On the basis of banding records, spring migration started around 1 April and ran through late May with a peak during mid-May Fall migration occurred from 1 August through late October. No obvious peaks were apparent in the fall, although slight bimodality occurred with peaks in late August and mid-September. Males migrated significantly earlier in spring but not in fall than did females. Though males stayed longer (4 d) on average than did females (3 d), the length of stay on the site during spring migratory stopover did not differ significantly between the sexes. All but one of the birds staying longer than 5 d were males. No significant linear relationship was found between original arrival date and length of stay during the spring. The mean mass change during spring stopover was the same for males and females (0.4 g). The data presented here suggest that the timing of onset of migration rather than the rate of migration may be more important in establishing the earlier vernal migration of males.

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