Lifetime reproduction of a forest-dwelling owl increases with age and area of forests.

Loss and alteration of habitats by human actions are the largest worldwide hazard to biodiversity and viability of populations. In boreal forests of Eurasia and North America the natural habitat is changing, mainly because of forestry practices and agriculture. Although there is evidence that the diversity and abundance of animal species are lower in intensively managed than in natural forests, very little is known about how the changes in habitat composition affect reproduction and survival. The best available measure of individual performance in the wild is lifetime reproductive success (LRS), the number of offspring produced during a lifetime, because it combines both survival and reproductive success to a single measure. We show that the LRS of forest-dwelling Tengmalm's owls (Aegolius funereus) increases with the proportion of old forest in the territory because of a higher number of breeding attempts, whereas it decreases with the proportion of agricultural land because of declining fledging success in years when prey populations crashed during owl breeding. These unique results provide an interesting insight into how human influence on the landscape can affect life-history traits of animals through various pathways.