Sex-specific foraging behaviour by a low-arctic, diving seabird over the annual cycle

Burke, Chantelle M. (2021) Sex-specific foraging behaviour by a low-arctic, diving seabird over the annual cycle. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

This thesis examines the seasonal foraging ecology of the Common Murre (Uria aalge), a circumpolar seabird with physiological adaptations for efficient pursuit-diving and a specialized reproductive strategy (male-biased parental care). The primary research objectives are to assess the behavioural strategies drawn upon by adult murres to survive a seasonally dynamic, Arctic-influenced marine environment, and to investigate how seasonal differences in parental care roles influence sex-specific foraging and survival strategies. To engage this question, I use bird-borne data loggers that collect behavioural observations relating to the distribution, diving and daily activity patterns of individual murres over eight months (July - February) in their annual cycle. Behavioural metrics are integrated with analyses of stable isotope ratios from a variety of tissues that provide corresponding information on seasonal trophic position and dietary niche breadth. Murres exhibited flexibility in their foraging behaviour over the annual cycle. This was evident in a switch from increased foraging effort with a specialized, high trophic level diet during periods of peak energy demand (summer chick-rearing and late winter) to significantly reduced foraging effort and a generalized, low trophic level diet during the less demanding post-breeding period. Energy savings during moult-induced flightlessness and a flexible moult schedule facilitated by a resident, over-wintering strategy resulted in low energy demands during the post-breeding wing moult. I hypothesise that the post-breeding period represents a buffer event in the annual cycle of adult murres, and may be a key component of survival for a seabird with an otherwise costly pace of life. Single-parenting males spent twice as much time foraging (self and offspring provisioning) relative to independent females (self provisioning only) and occupied relatively poor quality habitat over the estimated 63 days of paternal care at sea. Despite this, there was no evidence of an energy constraint as single-parenting males consumed the same low trophic-level diet as independent females and allocated equivalent time to self-feeding. Nonetheless, adult males could face time constraints to rear their offspring to independence and complete post-breeding wing moult before the onset of winter if energy limitations during poor-food years are resolved by the extension of either (or both) fitness-related activities. During late winter, murres experienced a significant increase in estimated daily energy expenditures (DEE), driven in part by high thermoregulatory costs during prolonged exposure to cold water. Murres were able to overcome this energetic challenge by pushing the limits of their diving capabilities but regardless, late winter appears to be an extremely challenging time in their annual cycle. Overall, this thesis demonstrates remarkable behavioural plasticity by murres over their annual cycle, characterized by highly plastic foraging tactics, dietary strategies and flexibility in the scheduling of wing moult, which may allow them to mediate some of the environmental disruptions predicted to occur with climate change. Yet, persistent declines in the biomass and condition of capelin Mallotus villosus, the keystone forage species in the NW Atlantic food web and the primary prey of breeding murres (and their offspring) could challenge this resiliency.

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