Inland and Coastal Swamp Sparrows Use Different Nesting Strategies
The 2 subspecies of swamp sparrows found in Maryland and Delaware have different strategies for raising young. The inland subspecies lives in the cool mountain bogs of Maryland, only a few hundred miles from its coastal cousin found in the salt marshes along the Delaware Bay.
The coastal birds tend to lay fewer eggs in a nest than their mountain relatives, but often re-nest several times during the breeding season. Recent research suggests 2 likely reasons for this disparity.
First, the coastal plain birds' nests suffer from more predation. Second, since the temperatures are higher along the coast, fewer eggs hatch. So for the coastal plain swamp sparrow, the adage "Don't put all your eggs in one basket" makes perfect sense.
This article summarizes the information in this scientific paper:
Olsen, B., Felch, J., Greenberg, R.S. and Walters, J. 2008. Causes of reduced clutch size in a tidal marsh endemic. Oecologia, 158(3): 421-435.
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