Growth and organ development in Greater Snow Goose goslings

Abstract

The tissue allocation hypothesis states that functional maturity and rapid embryonic growth are incompatible at the tissue level. This could explain why precocial birds, which have more mature tissues at hatching, grow more slowly than altricial birds. We evaluated this hypothesis in Greater Snow Geese (Chen caerulescens atlantica), which nest in the high arctic where the growing season is very short. We examined growth patterns and dry-matter content (an index of tissue maturation) of various tissues, and the accumulation of fat in 176 goslings collected from hatch on Bylot Island, Northwest Territories, to their staging area at Cap-Tourmente, Quebec (1 to 110 days). The mass-specific growth constant (K = 0.093) of goslings was among the highest of all precocial birds, including ducks. Goslings fledged at only 68% of adult mass, a low value compared with other species. The timing and rate of growth differed among tissues, indicating major shifts in the allocation of protein during growth. Growth rates for body mass, body ash, and total body protein were moderate. Leg muscles and digestive organs had an early and rapid growth rate. Breast muscles had one of the high est growth rates but started to grow very late. Fat accumulation began after fledging, forcing goslings to start southward migration with very little fat reserves. In early-growing tissues (digestive organs and leg muscles), water content was low at hatch, peaked before fledging, and decreased thereafter. This contrasts with the typical pattern in birds of peak values at hatch followed by a monotonic decline during growth. The high dry-matter content of tissues at hatch could be an adaptation to increase thermogenesis of goslings in cold water. A strong inverse relationship between exponential growth rate and functional maturity was found in breast muscles but was absent in early-maturing tissues. Ecological factors seem more important than embryonic constraints in explaining fast growth rates in geese.