Notes on the Feeding Behavior, Metabolism, and Weight of the Saw-whet Owl

Why is the Galipagos Lava Gull the Color of Lava?-"LavaGull" is a suitable name for Larus j&ginosus, since the species not only resembles dark lava in co!or but also because it spends much of its time on the lava rocks adorning the shores of the Galapagos Islands.Even the bill of this endemic gull is nearly black, the extensive distal red coloration found on bills of most gull species having been reduced to a median line less than 2 mm.wide and 8 mm.long (notwithstanding the erroneous description of "bill red," in W. B. Alexander, Birds of the Ocean, ed. 2, 1954:88).Charles Darwin (Voyage of the Beagle, Bantam ed., 1958:329) noted the dark color of the Lava Gull and of other Galapagos animals and ended his discussion with a carefully worded speculation hinting that coloration is related "perhaps to the conditions of existence being generally favourable to life."Today most biologists would agree that dark coloration has probably been evolved through natural selection, although the selective advantage of such coloration is still a matter for speculation in most cases.Bowman (Univ.Calif.Publ.Zool., .58,1961)has provided a convincing interpretation of evidence that predation pressure has caused the cryptic coloration in Darwin' s finches (Geospixinae) .It wourd be natural to suggest that all dark animals in the Galapagos have evolved melanism to escape predators.However, I wish to propose an alternative explanation for the Lava Gull' s color and thereby introduce caution concerning attempts to ascribe the dark coloration of all Galapagos animals to an identical cause.Gifford (Prcc.Calif.Acad.Sci., 2, 1913:44) described the Graceful Petrel (Oceanites gracilis) and the Man-o' -War Birds (presumably both Fregata magnijicens and F. minor) as competitors of the Lava Gull, since all these species eat refuse.Twice, on Tower Island in the Galapagos in November, 1962, I noted individuals of Fregota minor swooping down on pieces of fish we had cast on the sand beach in order to attract Lava Gulls; each time the Man-o' -Wars routed the gulls present.A perusal of the literature and of field notes by others would probably multiply such observations.My suggestion, then, is that the Lava Gull is cryptically colored in order to hide its presence on lava shorelines, not from predators (as it appears to have none), but, rather, from competing scavengers.My thanks go to Mr.