Food provisioning and growth in the Atlantic puffin fratercular Arctica: an experimental approach

Abstract

This study provided Puffin chicks with an additional 25g of food per day during the period of maximum growth rate to determine whether: 1) adult puffins can evaluate and respond to the nutritional requirements of their chicks, and 2) whether growth parameters (rate and elevation) of structural body components are flexible in response to variable levels of nutrition. Adult provisioning rates were significantly reduced in response to supplementary feeding, with experimental chicks receiving a mean of 2.1 feeds/d(^-1) compared to control chicks which received 4.7 feeds/d(^-1). There was no difference in the mean weight or energy content of the loads delivered to both groups, suggesting that the adult response to supplementary feeding took the form of a decrease in feeding frequency rather than a decrease m the size or nutritional quality of the load. No significant differences were found between the experimental and control groups in both the growth rate of overall body size and body weight. Neither was there a difference between groups in body mass elevation (mass corrected for age). However, chicks provided with supplementary food grew significantly larger for their age than control chicks. The fact that control birds were smaller but body masses were identical between the two groups suggests that control birds were not energy limited but nutrient limited; supplementary food may have provided the additional nutrients allowing structural tissues of experimental birds to grow larger. Differences in body tissue composition, and thus differences in metabolic energy requirements, may have been indirectly responsible for the similarities in body mass between the two groups. Identical growth rates between the two groups may have been a result of constraints acting at the physiological level, which prevented any further increase in rate once maximum size was reached for a given nutrient intake. In conclusion, variation in the quality or quantity of Puffin nestling diets does effect growth patterns of structural body components. Environmental sources of morphological variation should not be neglected in studies of phenotypic variation in birds.