To study the time course of feeding-induced thermogenesis (heat increment of feeding, HIF) in an avian species with a crop, we measured the HIF induced by a bout of feeding in the domestic pigeon (Columba livia). Six birds were fasted for 24 h and then allowed to eat for 40 min by illuminating an otherwise darkened metabolic chamber. Oxygen consumption (MO2) and respiratory quotient (RQ) were measured by indirect calorimetry, deep body temperature (T_b) using intra-abdominal data loggers (iButton Thermochron, DS1921H, implanted 1 week earlier under isoflurane anaesthesia, 4%; post-operatively, buprenorphine was given for analgesia (0.1 mg/kg i.m.)) and shivering thermogenesis by electromyography (r.m.s. of electromyograms) from the pectoral major muscles for 5 h after feeding. All animals were humanely killed at the end of the experiments. At 23°C, feeding was followed by a significant increase in MO2 from 12 to 16 ml min kg^-1 and RQ from 0.75 to 0.90 that lasted for several hours (repeated measures ANOVA). At 0.5°C, feeding did not change MO2, although RQ increased as at 23°C. Such results generally indicate that HIF substitutes for facultative heat production (shivering) in the cold. However, we found no difference in shivering between fed birds and non-fed controls in the cold (r.m.s. EMG about 60 μV in both groups). Furthermore, the instantaneous increase in MO2 did not correlate with the amount of food eaten at either temperature, but T_b was higher in fed birds than in controls. Additional experiments showed that 90% of the food ingested was still present in the crop 1 h after feeding indicating a regulated transit of food from the crop to the alimentary tract. We conclude that the additional thermogenesis at 23°C was not necessarily a result of true HIF induced by digestion, but may have resulted from a shift in basal metabolic rate or even an increase in facultative thermogenesis (although shivering was not measured at 23°C). Both of these may be triggered by neuroendocrine signals induced by the mere presence of food in the crop.