Starlings on defence manoeuvres

Our local starlings are putting on a dazzling display every evening.  The murmuration has a purpose and is not just for our benefit or for the starlings' enjoyment.  This type of behaviour has parallels with the shoaling of fish or the herding of mammals and is a defence strategy.  It is an emergent behaviour, that is it arises from the combined effect of individuals following very simple rules without any central coordination.  The starlings do it as a defence against predators, in this case against sparrowhawks.  The beauty of it all, to our eyes, is a by-product.

It has been exciting to watch the sparrowhawks trying to catch their dinner.  They appear soon after the first starlings arrive over the reserve, shortly before sunset.  Here you can see one sparrowhawk flying close to the murmuration (top right) but the starlings are well aware that it is there and can't catch them.

This is probably roughly a sparrowhawk's eye view of the murmuration as the starlings fly over the hide.  The predator is disorientated by the numbers and movement and can't lock onto a target.

The experts' assessment of the numbers this week is 25-30,000.  The noise as they fly overhead is like surf on the shore and we can feel the downdraught from their wings as they fly by close to the hide.  The starlings' aim is to get down into the safety of the reedbed as fast as possible and they seem to pour out of the sky.

Thousands upon thousands vanish into the reeds in seconds until you would think there wasn't room for any more.

The sparrowhawks have changed strategy by this time and skim over the reeds, hoping catch a starling unwisely putting its head up.  At this stage it is nearly dark so the photos are poor quality but at least you can see what is happening.  Modern camera sensors are good but not as good as a human eye.  Presumably a sparrowhawk's eye is even better.

If they fly against the sky the camera has a better chance of focussing.

The hunters dash back and forth as the starlings continue to pour into the reeds but we didn't see one caught.  By the time we left all the birds were down in the reeds and it was almost completely dark.  This view into the reeds shows the birds drinking and bathing, even as latecomers arrive above them, so they look fairly relaxed.  One sparrowhawk dived into the reeds as well and didn't reappear so I don't know whether it managed to catch its supper.

To give you an idea how dark it is, here is an unprocessed version of the photo above, the best the camera could manage, even with an ISO of 12,800.

I have also seen the birds leave in the morning, before sunrise.  There is a very loud chattering noise in the reeds and suddenly they all take off in unison with a roar of wings.  They fly fast and very low over the reeds and skim the trees, looking like smoke pouring from the reeds.  They were again pursued by the sparrowhawk, this time looking for its breakfast.