Daily energy expenditure and short-term reproductive costs in free-ranging Eurasian Kestrels (Falco tinnunculus)

1. The relationship between daily energy expenditure (DEE), measured using the doubly labelled water technique, and flight activity, rate of food delivery, daily mass change and body condition was studied in a population of the Eurasian Kestrel in Finland. Only female Kestrels were recorded for flight activity. 2. In female Kestrels, the time that the bird was in sight was negatively associated with DEE, while ambient temperature, flying activity, daily mass change and body condition were not related to DEE. When body mass and temperature were controlled for, there were still no associations between residual DEE and variables of flight activity, rate of food delivery, daily mass change, or body condition. 3. In male Kestrels, there was a tendency for DEE to be associated with condition at the initial capture, but this relationship disappeared when body mass and ambient temperature were controlled for in the analysis, Daily mass change and rate of delivery were not associated with DEE or residual DEE in male Kestrels, 4. Energy expenditure in both male and female Kestrels increased faster than expected with body mass, suggesting that heavy individuals were more active than light ones, that expenditure increased faster than expected with body condition, or that the relative costs of flight increased with body mass.