I was appalled by a gruesome discovery this morning just outside our front door. The head of one of our magnificent ospreys had been severed and was lying on the ground. A pair of ospreys has been nesting in a tall Norfolk Island pine directly over our house for the past 20 years. I immediately suspected that the perpetrator was one of a pair of great horned owls that have been hooting from a stand of Australian pines next door. Great horns take over nests of other bird species and are well known to evict even large birds of prey such as ospreys and eagles. We had heard a commotion in the early morning hours and thus surmise that one of the ospreys had been reluctant to abandon its cherished nest and was attacked and killed by the great horned owls. These owls are huge and ferocious and completely dominating at night when they can see clearly while the daytime hunting ospreys cannot.
This is a painful lesson in the ways by which natural events sometimes unfold. These can seem cruel, but conflicts over territory and breeding sites can be extremely fierce and terminal for the loser. We are sad for our poor osprey but have been taught a lesson in nature’s classroom.
An interesting evolutionary question would be why great horned owls do not build their own nests as do most birds? One answer would be that they thus save themselves some effort and can by their own might usurp the breeding territory of other birds. There is of course no competition for food between ospreys (fish eaters) and great horned owls which feed on a wide variety of terrestrial vertebrate prey (birds, mammals, reptiles). So the competition may be primarily for scarce nesting sites and/or perhaps even the nests themselves, which require considerable effort to construct. There is also the fact that an owl nesting near an osprey or eagle would likely be subject to considerable harassment during daytime since the owls might prey on the osprey and eagle chicks. So by removing the nesting osprey the owls eliminate a source of danger to themselves during daytime when they are most vulnerable.