Abstract

Telemetric eggs were used to monitor daytime incubation temperatures at Nankeen Kestrel, Falco cenchroides, nests on the outskirts of Canberra, Australia. During monitoring, only the females incubated. Once the second-last egg in the clutch was laid incubation began in earnest and temperatures averaged about 37˚C. Incubation temperature was not constant; rather, it varied according to the day of incubation and showed marked variation over the course of the day and between individuals. On average, temperatures increased about 0.6˚C per day until five days after the first egg was laid. After this, average temperature began to level off but continued to increase throughout incubation, at a rate of about 0.2˚C per day. Mean temperature was positively correlated with chick condition at banding; we suggest that this was because better-fed females have little need to hunt and can thus maintain higher mean temperatures. At successful nests the eggs were incubated for about 73% of observation time, less than for kestrels’ colder-climate congeners and suggesting that for kestrels in warmer climates such as in Australia the costs of incubation may be comparatively low.