Neonate reserves, growth and survival of Ross' and Lesser Snow Goose goslings
Slattery, Stuart Michael
The influence of egg size and brood dispersal on gosling growth and survival was studied in Ross' and Lesser Snow Geese hatched at Karrak Lake, N.W.T. Variation in neonate composition can influence growth, energetics and, possibly, subsequent dispersal patterns of young. Therefore, the relative nutrient profile and physiological development level of neonates in these two dimorphic species were examined by analyzing egg and gosling composition for seasonal, egg size and species-specific effects. Late laid eggs had less yolk protein and, in Ross' Geese, produced goslings with smaller pectoralis muscles. Since skeletal muscles are important for thermogenesis, this seasonal variation in muscle tissue may influence thermoregulatory abilities of late-hatched young. Egg composition varied isometrically with egg size. However, goslings from larger eggs were relatively smaller for their egg size yet contained the same relative nutrient content as goslings from smaller eggs. Because of their higher lipid:body size ratio, goslings from larger eggs were in better condition. Thus larger egg size may give an initial energetic advantage to goslings during periods of nutritional or thermal stress. Although no interspecific variation was observed for egg components, Ross' Goose goslings hatched with more protein for their egg size and larger gizzards for their body size. In addition, Ross' Goose goslings had less water per gram of lean dry mass than did Snow Goose goslings which indicates a greater functional maturity of Ross' Goose neonate tissue. Digestive efficiency, thermoregulatory ability and locomotor capacity may be relatively better in Ross' Geese and these characteristics may represent adaptations to metabolic constraints associated with smaller neonate body size and foraging requirements. Resource depletion around large nesting colonies may influence brood movements and subsequent growth and survival of nidifugous young. If per capita food availability increased with distance from the colony, then I predicted that broods settling farther from natal colonies should produce structurally larger and/or relatively heavier goslings than those broods feeding locally. I used radio telemetry to recapture marked broods and found indirect evidence of a nutrient gradient around the Karrak Lake colony. Broods dispersed 8-59 km away from Karrak Lake with Ross' Geese travelling farther than Snow Geese (19-59 km vs 8-21 km, respectively). These dispersal patterns may be a function of parental behavior, body size, bill morphology and nutrient requirements. For known age Ross' Goose goslings, birds reared farther from the colony were heavier for their body size than were goslings raised nearer to Karrak Lake. Body size varied randomly with distance in this sample. Both body size and condition varied positively with distance for Ross' and Snow Goose goslings of unknown age which were measured at marked brood recapture sites. A similar pattern was observed for body size in unmarked adults and this similarity may reflect common environmental effects during the growth period of adults and goslings. Although I found no distance effect on gosling survival, egg size was a significant determinant of within- (Snow and, possibly, Ross' Geese) and among-brood survival (Ross' Geese). Because goslings raised closer to the colony may fledge in poorer condition and thus may have lower first year survival, female philopatry to brood-rearing areas could indirectly influence parental fitness.