DO KESTRELS ADJUST THEIR PARENTAL EFFORT TO CURRENT OR FUTURE BENEFITIN A TEMPORALLY VARYING ENVIRONMENT

We examined the cues that Eurasian kestrels (Falco tinnunculus) may us e to adjust their parental effort (PE) under fluctuating food conditio ns in western Finland. The consequence of variation in the fitness ben efit expected from the current brood was studied by comparing PE of pa rents rearing broods of different fitness value, as estimated by body condition of offspring, and quality of breeding season (decreasing, lo w or increasing vole abundance). Brood size manipulations were carried our to evaluate the consequences of current brood size for PE. The pr oportion of the total time spent in flight hunting (hunting effort) wa s used as an estimate of PE for males and prey delivery rate for femal es. PE was not associated with offspring condition, but offspring cond ition increased strongly with prey delivery rate of males. Males did n ot change their PE as a response to brood size manipulation, and femal es only weakly responded to these manipulations. Also, parents did nor increase their PE in years of high offspring survival. These results suggest that kestrels did not adjust their PE to current benefits. In a temporally fluctuating environment, migrant kestrels that are nor te nacious to their breeding areas probably cannot assess the benefits of parental care (offspring number to breeding age). Parents apparently cannot rely on parameters like brood size or brood quality in their pa rental care decisions, and PE is invariably set to the level where par ental survival is not jeopardized.