Tuesday, 21 April 2015

The female Sparrowhawk and the 'missile' thrushes

There is a breeding pair of Mistle Thrushes in the park. Last week, one was busy finding earthworms on the lawn and carrying them neatly folded in its bill. This means they must be feeding young.  Today I heard the rattling call of annoyed Mistle thrushes. They use this call when they guard their berry trees in the winter, against Blackbirds and even much smaller birds like Chaffinches. The pair of them called and called from a tree. I tried to spot them and saw that a female Sparrowhawk was sitting on a branch. The Mistle Thrushes rattled and swooped over the hawk, the hawk ducked every time they dive-bombed her, although they didn't actually touch her.
 The female Sparrowhawk is an impressive raptor compared to the almost cute, much smaller, male. She is as large as a Woodpigeon, with broad chest and piercing yellow eyes. She can actually bring down Woodpigeons. Although the thrushes appeared fearless, they always stayed over the hawk, not underneath. The hawk moved onto an ash tree nearby, and although higher up, there were fewer leaves in the way, and after some trying I found a clear line of view and managed to take some photos and a video of the 'missile' thrushes dive bombing her. This behaviour, known as 'mobbing' involves potential prey individuals harassing or sometimes actually attacking predators when they are encountered. Mobbing is at its most intense during the breeding season. It is a behaviour that is not completely understood. One explanation, the 'move-along' hypothesis, is that mobbing diverts the predator attention from places where there are nests or young. When the Sparrowhawk's young hatches, they will be fed almost exclusively on fledglings, so harassing the predators might encourage them to move on, and hunt somewhere else.
Mistle thrush with worms in bill (14/4/2015)

The 'missile thrush' was my photo management software autocorrection, but I think it is actually quite fitting! This is an initially very shaky clip (no tree nearby to hold on). Watch out at 11 seconds.

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