Swamp Sparrow Family Planning
March 9, 2009
The 2 subspecies of swamp sparrows found in the Middle Atlantic States (e.g. Maryland and Delaware) of the United States 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 coast.
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.
