Saturday, 16 November 2013

Talking heads

I put a net up in the garden this morning with the aim of catching a few more Goldfinches for my study of their plumage features. This involves taking descriptions and measurements of various parts of the plumage along with a series photographs of each bird. The weather was ideal for catching being dull and overcast and 14 new Goldfinches were caught during the morning.

Side profiles of the heads of the 14 Goldfinches caught this morning, one of the standard photographs
 that I take of each bird. A few still had remnants of juvenile feathers.
The majority were sexed using the usual criteria but that assumes those criteria always hold true but unfortunately they don't. Some clearly had contradictory or borderline sexing features which shows that each of the established sexing criteria are not 100% reliable on their own but that is nothing new. However, I am also starting to find other plumage features that may help with sexing birds. One thing that these photos do show is the variation in bill size and shape and that is also known to relate to the sex of Goldfinches.

The red mask of this juvenile (first winter) bird is quite extensive and extends well behind the eye (above) indicative of male. The nasal hairs appear to be quite worn but are a pale greyish white which is more indicative of female. The lesser coverts were pale brown and more like those of a female. This is one of those birds that is probably better left unsexed although I suspect it is probably a male.

The red mask of this adult also extends behind the eye (above) but is generally less extensive than the previous bird. Nasal hairs are again greyish white in the main and indicative of female. The lesser coverts were pale brown also suggesting female. Other plumage features and a short wing length also indicated it was a female. This bird was sexed as a female but the extent of the red behind they eye could lead to confusion for some.
Another male type with extensive red mask and all other features were indicative of it being a male. This bird also had a very deep bill and convex culmen compared to all the others caught today.
Hopefully my study will help throw some light on the sexing of Goldfinches using plumage features but I suspect that it will mainly find that a significant proportion of birds are safer left unsexed or are only given a provisional sex..

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