Thursday, 28 May 2015

Crawford 27/05/15

Lesser Redpolls are still taking full advantage of the nyger feeders at Crawford and the feeders have needed topping-up every 3 or 4 days as a result. The weather was ideal for mist-netting this morning so I decided to fit in a short visit to see how many Redpolls were about. I expected most to be retraps but the morning got off to a great start with a control (a bird ringed elsewhere) and a new bird. Both were cracking males but one was much darker than the other and they show the variation that Lesser Redpolls can display. The paler example is the sort of bird that is sometimes mistaken for Common Redpoll in the field, especially when seen alone or in the company of darker individuals. Spring Lessers seem to be the most problematic with some seemingly becoming darker with wear and others becoming paler. They really were as different as they look in the photographs below and the paler bird stood out in the field too.

Control Lesser Redpoll Y781820
Lesser Redpoll Z414896
Examples of other types of colour variation were displayed by a couple of birds caught subsequently with one of these birds having a yellowish poll and another having a mixture of red and yellow. Both of these birds were retraps and had been ringed earlier this month.

Redpolls occasionally exhibit Xanthochromism whereby the red pigment in the plumage is replaced by yellow.  The cause is usually genetic but some forms of  Xanthochromism can be caused by diet. In my experience it seems to be more common in female Redpolls than males and the best examples I have seen have been adult females like this bird.

There is only a bit of yellow in the otherwise red 'poll' of this bird but it shows they can have both colours and not just one or the other.
The bird with the little bit of yellow in the crown was much more noteworthy for another reason as it also had a deformed bill. This bird was originally ringed and photographed on 1st May and I nearly posted pictures of it then. I don't know if this deformity is genetic, a result of trauma or disease but it was odd looking to say the least. Only the upper mandible was affected and an overgrowth, mainly on one side, formed a tube like nostril. The bird didn't seem hampered by the condition and was a good weight. The bird also had a brood patch that indicated she was an actively breeding female.

Lesser Redpoll with deformed bill, photographed 27/05/15
Lesser Redpoll with deformed bill, photographed 01/05/15
Lesser Redpoll with deformed bill, photographed 01/05/15
Although there were plenty of Goldfinches around very few came to the feeders but luckily one that did and was caught had been ringed elsewhere (a control). It also had interesting lesser coverts in that they were broadly tipped golden-yellow. Most male Goldfinches have lesser coverts that are all black or black with well defined brown fringes. However, a few can have more broadly tipped lesser coverts and those do are usually tipped golden-yellow rather than brown and this bird is a good example of that uncommon variation. There seems to be some form of exception to every rule when it comes to sexing Goldfinches from plumage features but then it wouldn't be interesting if it was easy and straightforward. The sex of this bird was confirmed by examination of the shape of the cloaca.

Male Goldfinch D954944 showing broadly tipped golden-yellow lesser coverts.
 Male Goldfinch D954944
A juvenile Tree Sparrow was also caught and this seems to be quite early judging by reports from nest recorders. The late spring means most Tree Sparrows are still on eggs or are feeding nestlings.

Juvenile Tree Sparrow.
Ringing totals (retraps/controls in brackets) at Crawford were: Lesser Redpoll 2 (9); Goldfinch (1); Tree Sparrow 2; Dunnock 1. All the ringing data has been sent to the BTO so I should be able to post details of where the controls came from in a week or two based on recent turnaround times.

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