Diet and reproductive success of Great Horned Owl (<i>Bubo virginianus</i>) at its northern breeding limit

Abstract

We studied the diet and reproductive success of Great Horned Owl (Bubo virginianus) at its northern range limit during an apparent high in the Snowshoe Hare (Lepus americanus) population. We performed diet analyses using images from fixed motion sensor cameras and pellet and prey remains collected at active nests, and gathered data on breeding success through camera and visual observations. Pellet data at 14 nests produced 1277 prey records consisting of 65–95% Snowshoe Hare biomass. Great Horned Owls ate 18 different prey types, with overall biomass consisting of 93% mammal, 7% bird, and less than 1% insects, frogs, and fish. The mean prey mass of 714 g (± 34 SE) was 2–25 times the mean prey mass of studies of this species at more southerly latitudes. Camera observations showed that Great Horned Owls delivered an average of 459 g/chick/d (± 75) throughout nesting. This was significantly (P = 0.005) higher than observations from Alberta, at 328–411 g/chick/d. Pellet/prey remains data showed that Great Horned Owls delivering a higher proportion of hares to their nestlings successfully raised more chicks (χ21 = 6.3, P = 0.012), highlighting the importance of this prey in the population dynamics of Great Horned Owl. In addition, we observed Snowshoe Hare removing pellets beneath nest sites, revealing an apparently undocumented bias to the use of pellet analysis.

Conspecific Carcass Removal from a Wind Project Study Plot by a Great Horned Owl (Bubo virginianus)

“…Great Horned Owls rely upon a broad prey base that encompasses many invertebrates and vertebrates, including other species of owls (Cromich et al 2002, Artuso et al 2020, Reynolds et al 2021). For example, they have been observed feeding on a freshly killed Short-eared Owl ( Asio flammeus ; Bluhm and Ward 1979), and fresh remains of this species have been found in Great Horned Owl nests (Killpack 1951, Wolhuter 1968).…”