The Influence of Territory Quality on Behavioral Activity, Mass Loss, and Tenure in Breeding Male Australian Fur Seals

Territory quality is a key determinant of male reproductive success and an important driver of population dynamics in pinnipeds. In Australian fur seals ( Arctocephalus pusillus doriferus ; AUFS), males rely on pre‐breeding energy reserves to acquire and maintain territories, linking competitive ability to body size and condition. The present study (2019–2021) investigated how territory quality influences behavioral activity, mass loss, and tenure duration in territorial adult males (bulls) at Kanowna Island, northern Bass Strait, the third‐largest AUFS colony. Although bulls were mostly observed resting, those occupying higher‐quality territories engaged in territorial behavior more frequently than those in lower‐quality zones ( r 2 = 0.27, P = < 0.05). Bulls occupying high‐quality areas also experienced greater daily losses in estimated mass index (EMI; r 2 = 0.73, P = < 0.01) while maintaining the longest tenure across the breeding season ( r 2 = 0.47, P = < 0.01). Larger males, indicated by greater size at arrival, showed the highest rates of daily EMI loss ( r 2 = 0.40, P = < 0.01). These results suggest that larger males with greater energy reserves can sustain the substantial energetic costs of defending high‐quality territories, highlighting how energetic capacity shapes reproductive success and competitive dynamics within colonies.