Defensive aggression in terns: Discrimination and response to individual researchers

Abstract

The defensive responses of roseate terns (Sterna dougallii) were studied during the middle of the breeding season when all reproductive stages (incubation, chick‐hatching, chick‐rearing) were represented, to determine the factors affecting levels of nest defense and whether terns responded differently towards a familiar versus an unfamiliar researcher. Defensive aggression generally varied as a function of researcher identity, time of day, section or location in the colony and nest density. These variables explained from 60 to 66% of the variation in defensive aggression. More terns mobbed one researcher with more dive attacks than the other researcher. Terns were more aggressive in areas where the chicks had just hatched and were most vulnerable. © 1993 Wiley‐Liss, Inc. Copyright © 1993 Wiley‐Liss, Inc., A Wiley Company