Sex differences in parental roles and diving behaviour of thick-billed murres, URIA LOMVIA, and Razorbills, Alca Torda, at the Gannet Islands, Labrador

Paredes Vela, Rosana. (2008) Sex differences in parental roles and diving behaviour of thick-billed murres, URIA LOMVIA, and Razorbills, Alca Torda, at the Gannet Islands, Labrador. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

There is no evolutionary, ecological or behavioural explanation for the partitioning of parental roles between the sexes in the Alcini, which includes murres (Uria), the razorbill, (Alca torda), great auk (Penguinus impennis) and dovekie (Alle alle); and why the male is the selected sex to accompany the chick to sea. I investigated parental roles and diving behaviour of two sympatric alcids, thick-billed murres, Uria lomvia, and razorbills, at the Gannet Islands, Labrador to determine whether sex-specific differences in energy expenditure at the time of departure explain male-only care at sea. Externally attached time-depth recorders (TDRs) negatively affected parental behaviour in male and female thick-billed murres. Partners of TDR-equipped birds compensated for the reduced parental effort in brooding and chick provisioning of their mates, with no differential responses between sexes. There was a temporal segregation of water depths, dive profiles, and food resources between the sexes in both species; these differences being stronger in thick-billed murres than in razorbills. Most murre females' self-feeding diving coincided with the vertical migration of crustaceans to surface waters; while male's self-feeding foraging occurred when prey were in deeper sections of the water column. Chick-provisioning diving was deeper than self-feeding irrespective of the sex or the time of day, suggesting equal parental effort allocation of the sexes underwater. Nevertheless, males had longer foraging trips than females probably due to the time spend flying to farther locations than females. Higher self-feeding rates and closer feeding locations may explain female's higher delivery rates at the breeding site. The longer time males spent brooding the chicks may serve to ensure parent-offspring vocal recognition at departure. Larger bill dimensions and higher levels of aggressive behaviour may confer males a better ability to protect the chick. In conclusion, differences in energy expenditure between the sexes did not seem to explain the male's parental role at sea. Instead, I proposed that the patterns of parental roles found between sexes was the result of a chain of events favouring male involvement in chick brooding and care at sea. A higher level of aggressiveness of the parent that escorts the chick to sea may have been selected for to ensure offspring survival, and as a result, parental roles developed at the breeding site to ensure male-only care at sea.

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