Influence of Solar and Geomagnetic Stimuli on the Migratory Orientation of Herring Gull Chicks

RESEARCH in avian migratory orientation has centered on the environmental stimuli that may serve as cues (see Adler 1970, Bellrose 1972, Emlen 1975). Most such studies have dealt primarily with long-distance migrants or trained homing pigeons (Columba livia) (Keeton 1974). Few experiments have explored the orientation mechanism(s) of nonmigrants, partial, or short-distance migrants. As Bellrose (1972) suggested, such studies may help illuminate the evolutionary development of avian migratory orientation. During June of 1972 and 1973 I studied orientation in the Herring Gull (Larus argentatus), generally considered to be rather sedentary (Smith 1959). The previous orientation studies with this species have been homing experiments testing the ability of displaced breeding adults. Griffin (1943) and Matthews (1952) both reported homing ability for Herring Gulls even from distances up to 872 miles (1404 km). Matthews (1952) concluded that visibility of the sun was related to homing success. Williams et al. (1974) likewise concluded that some mechanism other than landmarks may be involved in successful homing. Southern (1969a) found no evidence for the use of solar cues in Herring Gull orientation based on his homing trials (maximum displacement of 242 km). No doubt in close proximity to the breeding colony Herring Gulls use landscape features in homing (Southern 1970), but homing trial experiments have added little to the understanding of orientation cues involved in long-distance movements, particularly by inexperienced juvenile Herring Gulls. Furthermore, evidence for orientation abilities based on this experimental method is open to some question (Southern 1971). In light of these views and the likelihood that experienced adults have access to multiple cues, I decided to use Herring Gull chicks in indoor and outdoor orientation arena experiments designed to test the influence of various environmental stimuli on orientation behavior. Southern