Limited access to food and physiological trade-offs in a long-distance migrant shorebird. I. Energy metabolism, behavior, and body-mass regulation.
Previous experiments showed reduction of basal metabolic rate (BMR) in birds facing energetic challenges. We alternately exposed two groups of red knots (Calidris canutus) to either 6 h or 22 h of food availability for periods of 22 d. Six h of access to food led to a 6%-10% loss of body mass over the first 8 d, with nearly all of the birds' daily energy expenditures supported by body nutrient stores during the first 2 d. Birds responded by increasing feeding behavior and food intake, but the response was slow. There were no gains of mass before day 15, which suggests a digestive bottleneck and a period of physiological adjustment. Food-restricted birds exhibited decreases in pectoral-muscle thickness and BMR in association with a loss of body mass. Although a decrease in BMR saves energy, savings represented only 2%-7% of the daily energy spent in excess of that acquired during the deficit period. Red knots did not downregulate mass-independent BMR. On the bases of recent independent findings and the pattern of mass gain observed when food access was switched from 6 h to 22 h, we suggest that these birds routinely maintain nutrient stores as a buffer against periods of energy shortages, thereby precluding the need for downregulation of mass-independent BMR.
Vézina
François
F
Department of Marine Ecology, Royal Netherlands Institute for Sea Research, 1790 AB Den Burg, Texel, The Netherlands. francois_vezina@uqar.qc.ca
Petit
Magali
M
Buehler
Deborah M
DM
Dekinga
Anne
A
Piersma
Theunis
T
D000210:Acute-Phase Reaction / Q000276:immunology; D000818:Animals; D001522:Behavior, Animal; D001715:Bird Diseases / Q000209:etiology; D001833:Body Temperature Regulation; D001835:Body Weight; D046091:Charadriiformes / Q000033:anatomy & histology / Q000276:immunology / Q000502:physiology*; D004734:Energy Metabolism; D005260:Female; D005426:Flight, Animal; D005502:Food; D008297:Male