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Patterns of Seasonal Abundance and Social Segregation in Inland and Coastal Plain Swamp Sparrows in a Delaware Tidal Marsh
Citation:
GREENBERG, R., B. J. OLSEN, AND M. A. ETTERSON. Patterns of Seasonal Abundance and Social Segregation in Inland and Coastal Plain Swamp Sparrows in a Delaware Tidal Marsh. CONDOR. Ornithological Society of North America, Lawrence, KS, 112(1):159-167, (2010).
Impact/Purpose:
To add to the evidence that individuals of the coast can identify and preferentially interact with morphologically similar birds.
Description:
The Coastal Plain Swamp Sparrow (Melospiza georgiana nigrescens, CPSS) breeds in the coastal brackish marshes of the North American Mid-Atlantic States. During the non-breeding season, coastal brackish marshes are occupied by both this subspecies and two far more widespread interior-breeding subspecies (M. g. georgiana and M. g. ericrypta, INSS). We conducted surveys from September to May 2005-2006 and 2007-2008 in marshes used by breeding CPSS, almost all of which had been color-banded. This allowed us to determine the non-breeding occupancy of the breeding site by locally breeding individuals, non-local CPSS, and non-local individuals of the more distantly breeding INSS. Local CPSS disappeared from the breeding site by mid-October. However, the site was occupied by an many non-local CPSS from October to late November. Locally-breeding CPSS reappeared in April without any spring migratory peak. The INSS were abundant in the late autumn and appeared in smaller numbers throughout the non-breeding season. The seasonal pattern in CPSS was strikingly similar between the two survey years and the departure and arrival dates of this subspecies appear to coincide with changes in the average frequency of freezing temperatures. The INSS showed a more irregular temporal pattern that varied between years. Finally, an analysis of flock composition showed that during the peak of Swamp Sparrow migration in October and November, CPSS and INSS showed a strong tendency to segregate in subspecies-specific flocks. This observation adds to the evidence that individuals of the coast can identify and preferentially interact with morphologically similar birds.