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Acute and chronic behavioral effects of kelp gull micropredation on southern right whale mother–calf pairs off Península Valdés, Argentina

Taylor R. Azizeh*, Kate R. Sprogis, Raquel Soley, Mia L. K. Nielsen, Marcela M. Uhart, Mariano Sironi, Carina F. Marón, Lars Bejder, Peter T. Madsen, Fredrik Christiansen

*Corresponding author:

ABSTRACT: Kelp gulls (KG, Larus dominicanus) feed on the skin and blubber of living southern right whales (SRW, Eubalaena australis) off Península Valdés (PV), Argentina. The whales respond strongly to KG micropredation by changing their immediate (acute) behavior during attacks and their overall (chronic) surfacing pattern and body posture to minimize gull exposure. The energetic and large-scale behavioral consequences of these attacks are unknown. To address this, we quantified the effect size of both acute (during attacks) and chronic (not during attacks) responses by comparing the respiration rates, swim speed, and nursing behavior of PV SRW to undisturbed (control) SRW mother–calf pairs in Head of Bight, Australia, using unmanned aerial vehicle focal follows. Even when gulls were not attacking, PV SRW mothers and calves demonstrated ~50 and ~25% higher respiration rates, respectively, than in Australia. During attacks, PV calf respiration rates increased by an additional 10%. PV SRW mothers also frequently (>76% of respirations) exhibited chronic irregular breathing posture, causing the whale to potentially be expending extra energy by working against its natural buoyancy. Despite no significant increase in average maternal swim speed, 76 and 90% of gull attacks elicited strong behavioral reactions from mothers and calves, respectively. Overall, PV calves spent less time nursing during individual bouts compared to Australia but entered suckling position more frequently. Furthermore, kelp gulls seemed to show a preference for attacking previously wounded calves and at a higher rate. These chronic and acute behavioral effects may carry energetic costs, which could have long-term consequences on SRW survival and reproduction.