LOCOMOTION AND MUSCLE FUNCTION DURING POSTNATAL-DEVELOPMENT OF THE NORTHERN BOBWHITE (COLINUS-VIRGINIANUS) - EFFECT OF BODY-TEMPERATURE

Altricial and precocial birds differ in thermorgulatory and locomotor ability at hatching and consequently experience different ranges of body temperature. To test the hypothesis that thermal performance physiology matches the usual range of field body temperatures, we examined the effect of temperature on maximum running and jumping speeds of northern bobwhite chicks (Colinus virginianus) and on in situ contractility properties of the sciatic-gastrocnemius system. We found that the optimum body temperature for locomotor and neuromuscular performance and the thermal performance curves (variation in performance with body temperature) did not change with age among 1-, 8-, 15-, and 21-d-old chicks. This contrasts with a pronounced increase in optimum temperature and narrowing of thermal performance curves with age seen in an earlier study of 1- and 8-d-old red-winged blackbird nestlings (Agelaius phoeniceus). Thus, the stable thermal performance curves of precocial northern bobwhite chicks match a field body temperature that is probably fairly constant with age, whereas thermal performance curves of altricial red-winged blackbird nestlings shift ontogenically to track the higher and increasingly stable body temperature of older birds.