Diet and prey handling at a nest of the golden eagle (Aquila chrysaetos) in Oppland County, Norway

The diet and prey handling of a breeding pair of the golden eagle (Aquila chrysaetos) in Oppland County, Norway, was analysed with video monitoring of prey deliveries at the nest during the ten weeks that the nestling stayed in the nest. The study was conducted in a year with regional low abundance of microtine rodents and willow grouse (Lagopus lagopus). A total of 71 prey items was recorded delivered at the nest, 43 items of these were identified to species level and 26 to genus. One prey was only identified as a bird, and one prey was not identified at all. The most common prey were birds (68%). In terms of number of prey delivered, thrush (Turdus sp.) (41%), mountain hare (Lepus timidus) (27%), and willow grouse (20%) were the most numerous species. Mountain hare was the most important prey (67%), while thrush and willow grouse made 7% and 20% of total delivered biomass, respectively. Only one microtine rodent was delivered at the nest. No deliveries of sheep (Ovis aries), parts of a sheep, or other livestock was recorded at the nest. The male delivered most prey items (57%), of which the largest proportion was birds (69%). The nestling started to feed unassisted at an age of 41 days, and fed unassisted on birds earlier than on mammalian prey, in contrast to what found in previous studies. Deliveries of mountain hare and willow grouse declined throughout the season, while deliveries of thrushes increased. My study suggests that the golden eagle’s strategy when hunting willow grouse is win-shift, while the strategy on thrushes is win-stay. My study, as other studies based on video monitoring, has revealed a larger proportion of small prey species in the diet of the golden eagle, which is in contrast to studies based exclusively on prey remains and pellets. The high proportion of thrushes recorded indicates their importance in the golden eagles diet, especially in years with low abundance of other prey species. In consistence with other studies on the diet of golden eagle, mountain hare and willow grouse were the most important prey species in terms of biomass delivered.