Gull aggregation sites in Maine were survived by volunteers 22 Feb.-19
Mar. 1985-1987 to study differences in foraging site preferences betw
een Herring Gulls (Larus argentatus) and Great Black-backed Gulls (L.
marinus). Proportionately more Great Black-backed Gulls occurred at hu
man-made versus natural food sources and at sites with small total gul
l populations. The proportion of Great Black-backed Gulls at sites dec
reased as distance from coast increased. Numbers of Herring Gulls were
positively correlated with an index of the size of the human-made foo
d supply at foraging sites but numbers of Great Black-backed Gulls wer
e not. These results suggest that Herring Gull populations may have in
creased more rapidly than Great Black-backed Gull populations in the e
astern U.S. over the last 60 yr because Herring Gulls have exploited h
uman-produced food sources more readily than Great Black-backed Gulls.
Results corroborate other evidence showing that Great Black-backed Gu
lls are more strongly restricted to a coastal distribution than are He
rring Gulls, though the reasons why this might be so are unknown.