Friday, 4 July 2014

Sexing Goldfinches: summer update

My previous post on this subject has proved to be the most popular of my offerings by far; it continues to receive a good number of page views and seems set to remain the most popular post on this blog for a long time to come. The traffic sources indicate that it has been frequently viewed by those with an interest in keeping Goldfinches as cage birds in addition to bird ringers which it was primarily aimed at. There is clearly a lot of interest in this subject which is testimony to the difficulty that can be encountered in sexing a fair proportion of Goldfinches using plumage features alone. 

The fact that bird keepers can have difficulty telling the sexes apart is interesting as they have the ability to observe the birds they want to sex over a period of time whereas ringers only have a very brief opportunity when the bird is ringed and examined prior to release. Most confusion for ringers occurs in autumn and winter and appears to involve more first year birds than adults but that is when most Goldfinches are caught for ringing and first year birds often make up the bulk of those catches. The perceived greater difficulty in telling the sexes apart in first year birds may largely be a function of the sample sizes involved and may not be a real difference between the different age groups. 

It doesn't get any easier the more birds you catch either and this has been echoed by other ringers that have got in touch with me. The more birds you handle the more variation you get to see in the extent of the red face mask, appearance of lesser coverts and colour of nasal hairs and the combinations of those plumage features. The one thing that really hinders the refining of the sexing criteria and learning how best to apply them for me is the lack of known sex birds to test them with. I have previously said that I rarely catch Goldfinches during the breeding season when the presence of an incubation patch or cloacal protuberance can be used to confirm the sex of a bird. However I have put in a bit more effort in recent weeks and have managed to catch a few adult Goldfinches. Unfortunately I haven't caught anywhere near enough to see the full extent in plumage variation that is likely to exist but I still think it is worth showing images of some of the birds caught recently.

Confirmed male Goldfinch ringed 15/06/14:
The extensive and bright red mask on this bird is a good example of what a well marked male can look like.

The bird does have a few small white feathers on the front of its forehead otherwise the nasal hairs are black. In my experience it is not uncommon for male Goldfinches to have a few small white feather on the front of the forehead.

The lesser coverts on this bird have quite broad tips to the innermost feathers in particular, however they are gold coloured fringes rather than brown. This bird supports my view that any bird exhibiting such gold coloured (brownish yellow not brown) fringes to the lesser coverts, no matter how extensive, will be a male.

Confirmed female Goldfinch ringed 26/06/14:
The red mask is much less extensive on this bird and only just extends beyond the eye and combined with the greyish white nasal hairs (note some are worn or missing) make this a text book female. This bird also has some small white feathers on the front of the forehead like the male above.

The lesser  coverts on this bird are text book female too and form a brown patch at the shoulder.

The obvious incubation patch on this bird confirmed the sex as female.

Confirmed female Goldfinch ringed 30/06/14:
This bird has a more extensive mask compared to the previous female and clearly extends beyond the eye although nowhere near as extensive as the first male. The nasal hairs are mainly black or greyish black and there are no small white feathers to the front of the crown. The mask is more orange red than red but the colour of the mask can vary in shade and intensity and there is much overlap between the sexes.

The lesser coverts are similar to the previous female although the brown fringes are not quite as broad. However they still give the impression of a brown shoulder patch.

This bird also had a very good brood patch and confirmed the sex as female

Confirmed male Goldfinch ringed 30/06/14:

The red mask extends beyond the eye but not much further than the female above but the red is more crimson. The nasal hairs are clearly all black.

The lesser coverts have a mixture of narrow and broader brown fringes and some of the inner lesser coverts have brown bases. They are probably best described as intermediate between the text book examples of male (mainly black) and female (mainly brown). 

Confirmed male Goldfinch ringed 30/06/14:

This bird has a crimson mask that extends behind the eye. There is even red streak that extends a long way behind the eye where the red meets the black of the crown.

The lesser coverts are mainly black but all have well defined narrow brown fringes and this is quite common in males. It is fairly uncommon to find males with all black greater coverts in my experience although I have caught a few.

If you are wondering I didn't photograph the cloacal protuberance in any of the the males because I was ringing on my own and I just found holding the bird and blowing back the feathers and pointing the camera in the right place far too difficult but the sex of each male was confirmed in that way.  I hope to catch a few more adult Goldfinches this month while there is still the opportunity to confirm their sex and before they start to moult and if I do there may be another post on this subject later this month.
A further update can now be found by clicking here.

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