Daytime incubation temperatures in nests of the Nankeen Kestrel, Falco cenchroides

Telemetric eggs were used to monitor daytime incubation temperatures at Nan keen Kestrel, Falco cenchroides, nests on the outskirts of Canberra, Austra lia. During monitoring, only the females incubated. Once the second-last eg g in the clutch was laid incubation began in earnest and temperatures avera ged about 37 degreesC. 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 inc reased about 0.6 degreesC per day until five days after the first egg was l aid. After this, average temperature began to level off but continued to in crease throughout incubation, at a rate of about 0.2 degreesC 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 a nd 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 climate s such as in Australia the costs of incubation may be comparatively low.