The effects of age, timing of breeding, and breeding site characteristics on the reproductive success of the thick-billed murre, Uria lomvia.
Creators: name: De Forest, Leah Naoko.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1993
Subjects: subject: Biology, Ecology.

description: Age-specific reproductive parameters, including reproductive success, of young (four and five-year old) and older (&gt;7 years old) breeding Thick-billed Murres (Uria lomvia) were compared on a colony at Coats Island, N.W.T. in 1990 and 1991. Young birds laid smaller eggs later in the season than older birds. Older birds had higher hatching and reproductive success than young birds, but fledging success did not differ. The chicks of young birds at 14 days were lighter and smaller than those of older birds. There was a seasonal decline in hatching and reproductive success in both years for the total sample, but no seasonal decline in fledging success. Most losses occurred during the incubation period, with a decreasing likelihood of laying a replacement egg as the season progressed. Age-related improvement in breeding success may have been due in part to breeding experience. Second time breeders laid earlier than in their first year, and improved their reproductive success. Five-year olds breeding for the second time bred earlier and more successfully than five-year olds breeding for the first time. Differential survival in relation to reproductive success was not observed. Birds which performed poorly in their first year were not less likely to return to breed in the next year than birds which performed well in their first year. Different proportions of young and older birds breeding throughout the season affected the seasonal decline in reproductive success of the overall colony. Young and older birds separately showed no seasonal changes (except a slight decline in reproductive success in older birds in one year), but when combined they had a similar seasonal decline in hatching and reproductive success as the total sample. In order to control for differences in timing of laying between young and older birds, a sample of early laying, presumably older breeders were experimentally delayed c. 14 days. Age, rather than timing of laying influenced the decline in reproductive success. Young birds had significantly lower hatching and reproductive success than experimental breeders. Although the chicks of younger birds were significantly smaller than experimental chicks, there was no decline in food availability detected at the end of the season, suggesting that young birds were not able to provision their chicks as well as more experienced breeders. Breeding site characteristics had some effect on the reproductive success of young and older breeders. Older birds were more successful on sites which had neighbours. Site characteristics did not affect the success of young birds in 1990, but birds nesting on sites with neighbours and walls showed improved success in 1991. Young birds were less successful than older birds on all types of sites, and more likely to be found on suboptimal sites. The lack of decline in reproductive success with date when age was controlled, and the high reproductive success of experimentally delayed birds suggest that it is the competence of young breeders, rather than the date at which they lay, that determines their reproductive success. The high proportion of young Thick-billed Murres that lay later in the season may be the main cause of the seasonal decline in reproductive success for the colony as a whole.