Saturday, 20 June 2015

Sexing Goldfinches: easier said than done.

My previous posts on this subject are still attracting a lot of interest and my original photographic guide (link here) has been viewed thousands of times. When I put that guide together I was dealing with birds that had been caught in autumn and winter and consequently were not of known sex. However, that post illustrated the problems that can be encountered when trying to sex birds from the extent of the red mask, appearance of the lesser coverts and the colour of the nasal hairs. Around a third of the birds couldn't be sexed on plumage with a sufficient degree of certainty as they had one or more feature that was intermediate in appearance or they had what appeared to be contradictory plumage features.

I managed to catch a few birds last summer that I was able to sex from the presence of a brood patch in the case of females or a cloacal protuberance in the case of males. Although the sample size was quite small they threw a bit more light on the plumage features and on the extent of the red mask in particular. These birds confirmed that there is an overlap in the extent of the red mask between males and females and perhaps far more than is generally realised.

Bringing matters up to date I have caught more Goldfinches so far this breeding season than I have ever done before and I have been able to confirm the sex of these birds by checking them for the presence of a brood patch (female) or a cloacal protuberance (male). Being able to handle and photograph more birds of known sex has confirmed that there is a significant degree of overlap in the appearance of some males and females and others are what might be considered borderline. So lets have a look at some of these recent birds.

Z414635 was retrapped and photographed on 16/06/15                   Z414932 was ringed on 16/06/15                   
Z414933 was ringed on  16/06/15                                       Z414934 was ringed on 16/06/15    
Z414921 ringed and photographed 12/06/15.                   Z414888  retrapped and photographed 12/06/15  
The images above show 6 of the 13 adult Goldfinches that have been caught on my last two visits to Crawford. These birds are broadly similar in appearance but having said that there are some differences in the extent of the red mask with Z414934 (middle right) having the most extensive and Z414921 (lower left) having the least extensive, both above and below the eye. All have some greyish or greyish white nasal hairs or greyish feathers at the front of the crown except for Z414934 (middle right). Some readers of this post may be happy to suggest the sex of some or all of these birds and there is certainly no harm in giving it a go. They represent almost half of the birds caught recently so they are not unusual examples by any means.

So what sex are they: well Z414635 and Z414932 (top left & right) are females and both had very good brood patches; Z414933 and Z414934 (middle left & right) are males and each had a bulbous cloaca; Z414921 (bottom left) is a male and also had a bulbous cloaca while Z414888 (botton right) is another female that had a very good brood patch. Had I caught these birds outside the breeding season I would have probably left several unsexed based on the extent of the red mask and colour of the nasal hairs. In fact  Z414635 (top left) was originally ringed on 18/01/15 and I left it unsexed at the time and that was using all the plumage features including the appearance of the lesser coverts. However, I did make a note that I thought it was possibly a male so it was a really useful to retrap this bird and find out that it is a female and that I nearly got it wrong. 

The other feature that is usually checked when using plumage to sex Goldfinches is the appearance of the lesser coverts. The images below show the lesser coverts of the birds above and in the same order.

female                                                                                   female    
male                                                                            male      
male                                                                                               female
Some ringers don't have much confidence in the appearance of the lesser coverts when it comes to sexing Goldfinches but I think they are just as useful as the extent of the red mask. The image of the lesser coverts that stands out to me is female Z414735 (top left) which is quite unusual as it has mainly black lesser coverts with very little in the way of brown fringes. I have never seen a female Goldfinch with so little brown in the lesser coverts before and that, in combination with the extent of the red mask, is why I even thought it may be a male when it was originally ringed in January. The other birds more or less conform to the general rule that females have mainly brown lesser coverts or very broadly tipped brown lesser coverts while those of males are black or mainly black with well defined and usually narrow brown fringes although Z414934 (middle right) has quite broad brown fringes for a male but they are really well defined. It is worth noting that the black portion of the lesser coverts is usually deeper black and glossier in males than it is in females but as with all Goldfinch plumage features there is some overlap.

There is one more confirmed sex bird that I should show in this post to illustrate another variation in the lesser coverts. I used photos of this bird (D954944) in a recent post because it was a control and I mentioned its appearance then. The bird is a male but it had lesser coverts that looked more female like. However, the lesser coverts were mainly a golden-yellow or broadly tipped golden-yellow rather than the usual brown. It was originally ringed on 09/11/14 as an adult but wasn't sexed at that time. I can only assume the unusual appearance of its lesser coverts played a part in the decision not to sex it when it was ringed. Some may see examples like this as a reason to treat the lesser coverts as an unreliable feature but I simply see it as another variation to be aware of.

Male Goldfinch D954944 photographed 27/05/15
I would love to be able to say that I have found a reliable way of sexing all Goldfinches from their plumage but unfortunately I can't. The more I look at the plumage of birds that have had their sex confirmed by other means the more overlap in the plumage features I see. It is far too easy to get overconfident when trying to sex Goldfinches from their plumage and I know I have been guilty of that in the past. I can't give a definitive figure for the proportion of birds that can't be safely sexed on plumage alone as the time of year will make a difference. Autumn birds present more problems than late winter birds as the protracted moult of the head feathers can make a difference to the appearance of the extent of the red and nasal hairs. Whatever the figure is it is likely to be significant and it could be as high as 30%.

Whatever your view is on this subject I hope you find the photographs of known sex birds useful at least. Some blogs and guides only show images of males and females that have very obvious differences in appearance similar to those below. Those birds are not the problem and simply making reference to the variability of the species doesn't show the points of overlap where accurate sexing starts to become more difficult or impossible using the plumage features discussed. I hope this post has gone some way to rectifying that.

I know it is obvious but Z192897 on the left is a male and D725790 on the right is a female. These images are similar to those that are often shown and described in sexing guides but they don't tell the whole story as they are not typical examples of most males and females.

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