Gray catbirds begin their nocturnal migration to wintering grounds in late August and early September. The last of the stragglers are now passing through northern New England. Catbirds winter from the southern New England coast south to Panama, with concentrations on the U.S. Gulf coast and the Yucatan Peninsula. Those individuals that winter in the Yucatan Peninsula and Central America cross the Gulf of Mexico, and in order to do so they put on so much fat (during fall migration their mass may increase to 150% of lean body mass) that it approaches the upper limit of what flight allows.
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