This paper presents results from cooling investigations on bird eggs run in nests of several songbird species with contact and contact-less infrared thermometry and with a false colour thermography demonstration of temperature fields on egg surfaces and of the protecting nests. All experiments were performed on single or on up to four (clutch situation) fresh quail eggs. Results indicate that typical cooling curves show a two-phase exponential behaviour consisting of an initial part of warming the still air and the inside surface of the nest and a second part of egg cooling itself. Single eggs lying open to environment may experience a reduction of the cooling rate to 32% when placed in an open nest and even down to 14% in a covered nest. This corresponds to a prolongation of the time to cool down to half of the initial temperature difference from 11 to 35 and 80 min, respectively. IR photos demonstrate the strong thermal gradients of about 10 K of clutch eggs from the inner contact zone to their blunt ends. (C) 2003 Elsevier B.V. All rights reserved.