Territoriality and Behavioral Correlates of Reproductive Success of Great Black-Backed Gulls

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Abstract
Territorial characteristics and behavioral correlates of reproductive success were examined in a population of great black-backed gulls (L. marinus). Territories were defended from the preincubation through the postfledging periods and 53% of the territories under observation increased in size following chick hatching. Territorial adults displayed significantly more high-level agonistic behavior toward non-neighboring intruders than they did toward neighboring intruders. Most agonistic interactions occurred between adjacent territorial neighbors; only small segments of territorial boundaries were consistent sites of intense agonistic interaction. Chick mortality was not related to percent vegetative cover, nearest-neighbor distance, territory size or intrusion pressure. Chick mortality was positively correlated with the number of contiguous territories and the frequency of agonistic interactions of male gulls. Both post-hatch frequencies of neighbor intrusions and intrusions by non-neighboring conspecifics were positively correlated with the number of contiguous territories but were not related to territory size. The time that adults left their territories abandoned during the post-hatch period was negatively correlated with the frequency of intrusions (by neighboring and non-neighboring conspecifics) and positively correlated with the number of chicks fledged.