Metabolic and developmental responses of alcid chicks to experimental variation in food intake

I tested whether the ability of chicks to suspend growth and developmental processes in response to food shortages is greater among alcids with food r esources that fluctuate over short time periods than it is among close rela tives with food that is continuously available. I examined changes in chick resting metabolic rate (RMR) in response to short-term food deprivation in horned and tufted puffins (intermittent food provisioning) and crested and parakeet auklets (continuous food provisioning). RMR was based on measurem ents of chick oxygen consumption rates (Vo(2)) under thermoneutral conditio ns. RMR of postabsorptive chicks scaled allometrically with body mass, and regression slopes were statistically indistinguishable among species. Mass- independent RMR of the same individuals decreased significantly after 48 h of food deprivation. The decrease in the mass-independent RMR was greater i n puffins (46.8% in horned and 47.4% in tufted puffins) than in auklets (29 .4% in crested and 23.7% in parakeet auklets). To test whether the observed decrease in RMR was due to less energy being allocated to growth, I examin ed developmental responses of horned and tufted puffins to experimental var iation in rates of food intake. I found retarded growth rates in body mass, skeletal elements, and feathers in chicks experiencing low rates of food i ntake. The retardation of growth processes extended the developmental perio d, My findings suggest that developmental plasticity in juvenile alcids mig ht be related to temporal variability of prey in oceanic environments.