Parental roles of male and female thick-billed murres and razorbills at the Gannet Islands, Labrador

We studied female and male parental roles in two sympatric auks, thick-billed murre (Uric lomvia) and razorbill (Alca torch), with initial biparental care at the breeding site and later exclusively paternal care at sea. Our study addressed the following two questions: Why do males accompany chicks to sea?, and How do the sexes allocate parental effort at the breeding site before parental care at sea begins? We tested the hypothesis that males care for chicks at sea because they are in better condition at the time of chick departure as a result of female-biased parental effort at the breeding site ('nest'). Breeding success and duration of chick-rearing did not differ between the two study years in either species at the Gannet Islands, Labrador. At the breeding colonies, females of both species provided more food (murres: 2.84 +/- 0.18 loads day(-1); razorbills: 2.02 +/- 0.11 loads day(-1)) to their chicks than males (murres: 2.26 +/- 0.12 loads day(-1); razorbills: 1.42 +/- 0.09 loads day(-1)), and males spent more time brooding the chicks. These differences were chick-age dependent in both species, with females providing more meals to chicks older than two weeks. Razorbill males spent more time with chicks greater than two weeks old, while murre male's attentiveness of brooding did not vary with chick age. In both species, males (murres: 3.04 +/- 0.3 h day(-1): razorbill: 3.30 +/- 0.2 h day(-1)) performed longer foraging trips with meal delivery than females (murres: 1.23 +/- 0.4 h/day; razorbill: 2.50 +/- 0.4 h day(-1)). Thick-billed murres showed a consistent diurnal pattern of egg and chick attendance: females were usually found at the breeding site during the day whereas males were found there early in the morning and at night. In contrast, razorbill's timing of attendance was much more variable and did not differ between sexes. Despite these differences in timing of breeding site attendance between species, males of both species spent twice as much time as females engaged in the defence of the egg or chick at the breeding site, which suggest male-biased capability of protecting the chick at departure. Overall our data indicated different female and male parental roles at the breeding site but not a female-biased allocation of time, energy and risk as predicted. In fact, males seem to provide equal if not more parental effort than females prior to the time of colony departure. We propose that the patterns of parental roles found between sexes is the result of a chain of events favouring male involvement in chick brooding and care at sea.