COLONY LOCATION BY LEACH'S PETREL

LEACI-I'S Petrel, Oceanodroma leucorhoa, is one of a number of Procellariiformes that locate nest burrows under a forest canopy at night (Table 1), although some of these species also nest in nonforested terrain. During a study of the sensory bases of navigation in Oceanodroma leucorhoa breeding on Kent Island, New Brunswick in the Bay of Fundy (Grubb, 1971), I tested the possibility that incipient breeders of this species use senses other than vision to find active colonies under the Kent Island spruce-fir forest in which to begin nest building. Leach's Petrels, like many seabirds, do not reproduce until several years old. Petrels spend the first 2 years of life at sea, visit breeding islands during their 3rd and 4th summers, and generally start breeding during the 5th summer (Huntington and Burtt, 1970). Mist netting has revealed that many young birds with downy brood patches (brood patches of breeding adults are bare and vascularized) occur among the thousands of birds coursing over Kent Island each summer night from mid-June to September. I have watched petrels investigating nooks and crannies on the forest floor. Perhaps these are 3and 4-year-olds hunting for burrow sites. The distribution of petrel nesting colonies within Kent Island's forests is dumped, sections of seemingly good nesting habitat remaining empty. Petrels digging new burrows probably find colonized areas by other than visual means as the tree canopy conceals the colonies. Sounds from existing colonies might help young birds establish burrows there. Leach's Petrels have two calls: (1) the chatter call, a stereotyped pattern sequence of eight or more syllables with a descending cadence voiced by birds in flight, on the ground, and very commonly by breeding birds just after entering their burrows, and (2) the long, drawn-out purring call of indefinite length ("r-r-r-r-r-r-r-r-ooee-churr-r-r-r-r-r-r-r-ooee-chur, etc."; Ainslie and Atkinson, 1937), given rarely in flight or on the ground, but commonly in burrows, often as duetting by mated pairs. On Kent Island Huntington nets petrels attracted to unnaturally loud tape recordings of both calls. A potential olfactory stimulus is also present. The typical musky petrel odor permeating the area around the burrows is apparent to the human nose. Procellariiformes have highly developed olfactory organs (Bang, 1966). Adult Leach's Petrels apparently use a sense of smell to find their individual nest burrows at night under the Kent Island forest (Grubb, 1971). It seems, then, that birds seeking breeding sites