Consistent individual variations in aggressiveness and a behavioral syndrome across breeding contexts in different environments in the Black-tailed Gull

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Individual behaviors of animals do not evolve separately but do so in association with other behaviors caused by single shared genetic or physiological constraints and/or favored by selection. Measuring behavioral syndromes which are suites of correlated behaviors across different contexts, therefore, provides better understanding of the adaptive significance of variations in behaviors. However, studies that have examined the behavioral syndrome in wild animal populations in changing environments are in the minority. We measured behavioral syndrome among anti-predator nest defense, territorial defense, chick-provisioning, and mating behavior of male Black-tailed Gulls Larus crassirostris in two successive years with different conspecific territorial intrusion risks and food conditions. Males with high levels of anti-predator nest defense (aggressive anti-predator defenders) against the decoy of crows (an egg-predator) defended their territory against conspecific intruders more frequently than did other males (non-aggressive anti-predator defenders) independently of the risk of intrusion. Aggressive anti-predator defenders also fed their chicks more frequently than non-aggressive males, but only in the year of lower food availability. Taken together, this indicates that males show consistent aggressiveness regardless of breeding context (anti-predator and territorial defense), but they can regulate food provisioning according to food availability.