Home range size is determined by habitat composition but feeding rate by food availability in male Tengmalm’s owls

Animal populations are often limited by food and rearing offspring is energetically demanding. Life history theory predicts that parents of altricial bird species will often reduce their current reproductive effort when given supplementary food. Previous food supplementation studies have mainly focused on effects on female parents, while the importance of paternal behaviour has largely been neglected. We addressed the effects of natural and experimentally increased food abundance on male ranging behaviour and provisioning rate, female and fledgling condition, and final reproductive success, in the Tengmalm’s owl, Aegolius funereus, a species with obligatory biparental care. We found that males adjusted their parental effort by reducing provisioning rate at food-supplemented nests. Food supplementation induced an increase in body mass of females, and in body mass and haematocrit levels of fledglings. This suggests that the amount of extra food provided was enough for females to increase body condition sufficiently to start allocating extra resources to enhance the quality of current offspring. While the home range size of radiomarked males was not affected by food supplementation, it decreased with cover of spruce forest, which is a habitat that is denser in structure and richer in prey than pine forest and especially clear-cut areas. This suggests that habitat-specific prey abundance and/or cover may be strong determinants of home range size for males. Overall, the results provide novel insights into how habitat quality and food supply affect male hunting behaviour and biparental care, and how this in turn is reflected in fledgling condition.