Black and white under the South African sun:: are juvenile Cape gannets heat stressed?

(1) We measured dorsal surface temperature (T-d). skin temperature (T-s) and body temperature (T-b) of adult (white plumage) and juvenile (black plumage) Cape gannets, Morus capensis, subject to high ambient temperatures. (2) Mean T-d and T-b of juveniles were significantly elevated compared to those of adults. (3) Mean T-s of older juveniles, which had down beneath their body feathers, were significantly lower than T-s of younger juveniles, indicating that the down provided insulation. (4) Juveniles spent a significantly greater proportion of time thermoregulating via evaporative cooling than adults. (5) The high thermal load of the dark plumage is presumably associated with major costs for the thermal and water balance of juveniles. (C) 2002 Elsevier Science Ltd. All rights reserved.