Sunday, 15 January 2012

Short-eared Owl (Asio flammeus) Búho Campestre

The Short-eared Owl (Asio flammeus) is one of my favourite winter birds in Spain. The Short-eared Owl breeds across much of Eurasia, North America and its also is resident on Cuba and Hispaniola, as well as parts of South America with all northern populations generally regarded as migratory. Their life span is around 5 years.
Although not normally covering huge migratory distances in Europe, they move south in winter from France and Germany. It could be that wintering birds could come from further afield but as yet I haven't been able to find any information on this It would be interesting to know more about them and I do try and check through any photos I've taken for rings or tags, but as yet I've had no joy. It's also really difficult to see their legs for rings, both perched or in flight.
A lot of studies have been done in North America on Short-eared Owls and there is some information on UK owls and migration on the BTO website but the papers published have to be bought. Here's a really good little film of a North American Short-eared Owl hunting beside a busy road on some marshland.

On the side of the main collector canal at La Janda the open grassed areas are thriving with colonies of small rodents and an ideal wintering area not only for the owls but for other birds such as the large influx of Black-winged Kites (Elanus caeruleus) that are with us right now. The kites have been nesting here in very good numbers over the last few years, although when there is a decline in rodent populations the kites will leave the area, often travelling a thousand kilometers or more to an area where they can find food and breed. Their nomadic behaviour would account for their success and spread into Southern Europe.
Black-winged Kites physical structure, nocturnal looking eyes, flight and hunting techniques are more like owls than any other raptor I can think of in the Western Palearctic.

You can trawl though the web and find information on a fair bit of research that has been done throughout Europe but particularly in North America, that investigates the effects on vole population dynamics. You can see a clear link between predators and specialised alterations in rodent breeding behaviour and their seasons. This seems to be apparent during some years, when Short-eared Owls and of course other raptors too, leave their wintering areas like La Janda, to return to northern areas to breed, thus allowing the Black-winged Kite population to profit by the Short-eared Owl's absence and coinciding with the prenuptual period of the kite's breeding season in the south.

Short-eared owls seek out and inhabit areas where small mammals, especially meadow voles are abundant. Effective food sourcing dominates their breeding sites, the number of wintering birds, the number of nesting pairs, and the number of eggs they lay and of course this affects the number of young they have. All of these factors can change from year to year based purely on food supply.
Breeding begins in March when both sexes begin defending territories and courting that involves elaborate flight displays, include wing-clapping, exaggerated wing-beats, and skirmishing.
Birds nest on the ground where the female creates a cup shape and lines it with grasses and her own down. Four to nine eggs are typical, but clutches as large as fourteen have been reported in years of peak small mammal abundance. Incubation, which is done by the female alone, lasts about a month. The eggs hatch asynchronously and fledging occurs about a month later.

Here are a sequence of photos I took this week of a Short-eared Owl hunting rodents. It was just getting dark as we watched the birds coming towards us, rising up and catching the last glimmers of sunlight and falling back into the shadows.

We came upon a roost of thirteen birds in a wild olive tree a few days ago. This was the largest number I have seen roosting together of this species.
I co-led a winter tour to Holland with Arnoud van den Berg a few winter's years ago and saw how the Long-eared Owls (Asio otus) roosted together in trees within villages in the colder north. Roosting together like this offers protection against predators such as Goshawk. Long-eared Owls are great birds to see at any time, but with up to a dozen or more birds in village front gardens in winter, was quite a sight to see!

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