Tuesday, 23 April 2013

Waxwing lyrical part 33 - full to bursting

Waxwing numbers have continued to decline as more birds have reached the desired weight for migration. This seems to be around 75g judging by the weights of the birds retrapped recently and means that around one third of their body weight will be made up of fat deposits. This will allow them to migrate a long distance without the need to stop and feed or with limited stop overs to top up and if bad weather halts their migration.

There were only 111 birds this morning give or take one or two. Only is probably the wrong word as 111 Waxwings in the garden was unimaginable just a few weeks ago but numbers have almost halved over the last week. This fits in well with the decline in sightings being reported across the uk. Some birds will already be well on their way back to the main breeding grounds in Russia and a few early birds may have even arrived at the closest breeding grounds in Finland and western Russia.

The Waxwings as they gathered at sunrise this morning (23/04/13)
Most of the remaining birds actually look really fat now so they may not be here for much longer and most are likely to depart over the next week with just a chance of a few lingering into early May. They also appear to be less agile and a bit more sluggish when taking off as a result of the extra weight they are carrying. This probably makes them a little more vulnerable when the Sparrowhawk attacks and predation by Sparrowhawks has increased over the past few days.

Fatwings (Bombycilla blubberus), These birds were still feeding at 19:40 this evening.

Fatwings (Bombycilla blubberus), The same two birds as above..
This bird is clearly very fat. It is the same bird as the one on the left in both photos bove.
I would like to be able to catch it for ringing and to see what it weighs.
I suspect it would be over 75g and could even be over 80g so is likely to leave any time now.
One birdwatcher witnessed a Waxwing being taken by a Sparrowhawk the other day but overall Sparrowhawk predation has generally been less than than it might have been. However the attacks do cause the birds to go elsewhere for long periods and if predation increases it could hasten their departure. Some Sparrowhawks in Aberdeen seem to specialise on Waxwings and you can find out more by clicking here.

You can see how some birds look much plumper than others.
The bird on the lower left is likely to be the light weight in this bunch.

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