Wednesday, 22 January 2014

Ageing Goldfinches: a photographic guide.

It has taken me a while to get round to writing this post but here it is for what it is worth. Goldfinches can be difficult to age at times and are even more difficult to sex. In this post I only look at ageing and it is mainly based on birds caught for ringing from September to December 2013. All the photographs labelled as adults (Euring age code 4) were retraps from previous years and therefore their age is not in question. This removes any bias towards showing photographs of birds that conform to the current published ageing criteria for adults or the risk of birds having been aged incorrectly. All the birds labelled as 1Y or juv (Euring age code 3) showed evidence of only undergoing a partial moult or hadn’t completed the partial post juvenile moult at the time of capture. Some still had obvious juvenile feathers in the red mask of the face but be aware even some adults can have a few white feathers in the face that give the impression of unmoulted juvenile feathers (usually pure white as opposed to buff).


Photo 1. 1Y Goldfinch showing a few unmoulted juvenile feathers in front of the eye.


Photo 2. 1Y Goldfinch showing 1 unmoulted juvenile feather below the eye and a few others still in pin.

Photo 3. Known adult Goldfinch with 4 pure white feathers below and  behind the eye (unusual).
When I started to photograph every Goldfinch that I caught I didn’t expect to learn as much as I have. One example being that the moult of both adults and juveniles can extend well into December with the feathers of the face being the last to be replaced. This has particular implications for sexing birds but that will be the subject of another post if I ever get round to writing it. This post has been difficult to put together and has already had several false starts. What photos do you use when you have so many to choose from and what level of knowledge do you pitch it at ? I am likely to come back to this post from time to time to add photos or statistics so it should be seen as a work in progress. Hopefully some of you, especially other ringers, may find it of interest.

Most juvenile Goldfinches in the UK only undergo a partial post juvenile moult but it is thought that a very small proportion may have a complete moult like adults. The proportion of juveniles that undergo a complete moult isn’t easy to measure but is likely to be insignificant in the UK, if it happens at all. I didn’t encounter any juveniles in active primary moult and only caught 3 (<1%) that had replaced a few central primaries. However I did find that many replaced one or more tertials and some of their tail feathers.

Photo 4. 1Y Goldfinch with all new tertials, the longest tertial is not fully grown. The new glossy black tertails contrasting with the juvenile secondary feathers.
Many juvenile (1Y) Goldfinches have 1 to 3, rarely 4 or more unmoulted old greater coverts (OGCs). These are best distinguished by the contrast in appearance of the black part of the feathers rather than the colour of the tips as illustrated in Svensson. The new (adult type) feathers have a glossy black appearance in contrast to the matt black of the juvenile feathers with the differences being a bit more obvious in males. Birds with retained old greater coverts are easy to age.



Photo 5. 1Y (Juvenile) with 2 OGCs


Photo 6. Another juvenile with 2 OGCs
Photo 7. 1Y (Juvenile) with 3 OCCs.
However, some juveniles moult all their greater coverts and I found that just under 35% of the juveniles I caught had replaced them all (sample size 94). This is a significant proportion and these birds can be more difficult to age. Some ageing guides suggest there is a contrast between the new greater coverts and the old primary coverts and alula in these birds and that (with practise) this can be used for ageing. I used to agree with that view but have found a similar level of contrast between these feathers in all the known adults and therefore it isn’t a feature that stands up to close scrutiny. Having said that it is worth checking the carpal covert as this feather frequently has a dirty buff or brown fringe at the tip in juveniles although a few may be all black like most adults. In adults this feather is generally all black but very rarely a few may have a slight greyish white fringe (never dirty buff or brown as in juveniles). This feature is more obvious when the feathers are relatively fresh, in autumn and the first half of the winter, but can last through to the spring in well marked individuals.


Photo 8. 1Y Goldfinch (Juvenile) that has moulted all the greater coverts but shows a buff fringe on the carpal covert. Most juveniles had a brown or buff fringe on the carpal covert but it could be very slight in some.


Photo 9. A tighter crop of photo 8 above. Note there is no more contrast between the  greater coverts, primary coverts and alula in this juvenile than in the adult in photo 10 below.




Photo 10. Known adult showing some contrast between the black of the greater coverts and primary coverts similar to juveniles that have replaced all their greater coverts. In addition there is contrast between the small and large feather of the alula with the large feather of the alula having a faint pale tip. This wasn't expected but was consistent in all the known adults. The difference was marked enough to make them almost look like feathers of different age.
The tail shape of juveniles is generally described as being more pointed than those of adults and that they usually show more wear. However, things are not quite that simple as you will see from the photos below. A large proportion of juveniles replace the central pair of tail feathers and some replace the outermost pair with the difference in wear and contrast between the black areas of the feathers identifying these birds (again the newer glossy black feathers contrasting with the more matt black juvenile tail feathers). A few may replace more tail feathers but it is very rare for juveniles to replace all their tail feathers (1 in 300 or less). I only caught 1 juvenile that had replaced all its tail and this bird was aged from the partial moult of its primaries. As ever with Goldfinches there is a lot of variation and more overlap in tail shape than is often appreciated or illustrated in ageing guides. 


Photo 11. 1Y (Juv) with a very pointed tail shape and all the feathers are of the same generation. There isn't much wear but the shape is the clincher. If all juveniles had tails like this ageing would be easy. In addition this bird had 1 OGC and had replaced 2 of the tertials.

Photo 12. This is where things get a bit more interesting. This is the tail of a 1Y (juv) but the shape is closer to that often illustrated for adults. This bird had replaced the central pair of tail feathers and had 3 OGCs. It had also replaced the middle tertial so there is no question that this is a juvenile.


Photo 13. Here is another 1Y (juv) tail with quite a broad and not very pointed shape. This bird had 2 OGCs confirming its age as can be seen in photo 6 above. It had only replaced the central pair of tail feather but you can't see the contrast from this angle and because of the shade from my hand.

Photo 14. Here is another example of a 1Y (juv) tail. This bird had replaced the central and outermost pairs of tail feathers. It had also replaced all its greater coverts and the innermost tertial.



Photo 15. Believe it or not this is also a 1Y (juv) tail that has worn to a very rounded shape. This bird had replaced all its greater coverts and tertials. The central pair of tail feathers had been replaced but don't stand out as being a different shape. However they were obviously newer and more glossy black in colour. Ageing as a juvenile was also supported by the extent of primary wear.
Photo 16. Here is another shot of the 1Y (juv) tail above that gives a better view of the left hand side of the tail and makes it easier to see the new and more glossy black central pair of tail feathers contrasting with the remainder of the old worn tail feathers.

The photos of the juvenile tails above are a fairly random selection and show the range of tail shapes that juveniles can display. Having an understanding of this variation is particularly important when determining the age of birds with no old greater coverts. All the photos were taken over a relatively short period in December and after the post juvenile moult is complete so it isn't a case of variation over a long period of time or before and after the post juvenile moult period. The level of wear and any contrast between new and old feathers are by far the most important things to look for when using the tail to age birds with shape being more of a secondary consideration.

So now for some photos of the tails of some known adults for comparison. All the photos below are of birds that were originally ringed in previous years and are not just birds that appear to show adult features.   
Photo 17.  Known adult. This blunt and rounded shape is what ringers generally think of as being a good adult shape but it isn't exclusive to adults as we have seen in photos 15 and 16 above in terms of general shape. However there is no obvious wear and all the feathers are of the same generation. 


Photo 18. This is towards the other end of the range of adult tail shapes being fairly pointed but with a rounded tip. Again there are no obvious signs of wear and all the tail feathers are of the same age.


Photo 19. Known adult Goldfinch tail. Similar to photo 18 above.


Photo 20. Known adult Goldfinch tail.

Photo 21. Known adult Goldfinch tail. Again similar to photos 18, 19 and 20. This is probably the most common adult tail shape. The one thing all the adults had in common was the lack of wear to the tail feathers and all the tail feathers were clearly of the same generation.

There is a footnote in Svensson that says birds with sub-terminal white spots on the outer 3 tail feathers are adult although most adults only have spots on the outer 2. This has been repeated elsewhere but is not correct. I have caught numerous juveniles with sub-terminal white spots on the outer 3 tail feathers over the years as shown below. However, there is a paper that suggests birds with 3 white sub-terminal patches can be confidently sexed as males. That will have to be discussed in a future post on sexing Goldfinches or why you shouldn't sex most Goldfinches as my findings currently seem to suggest.


Photo 22. Example of a 1Y (juv) Goldfinch with white sub-terminal spots on the outer 3 tail feathers taken at Spurn in 2006.
Photo 23. 1Y (juv) Goldfinch with white sub-terminal spots on outer 3 tail feathers. The outermost tail feathers have been replaced and have a more rounded tip but all the other tail feathers are juvenile.
Photo 24.  1Y (juv) Goldfinch with white sub-terminal patches on the outer 3 tail feathers. This bird was ringed 09/11/13 and had replaced all its greater coverts but all the tail feathers were old (juvenile).
The one ageing feature that I haven't illustrated with photographs so far is the difference in primary wear that is shown by juveniles compared to adults. The primaries are always worth checking and can be very useful for confirming a birds age. In juveniles the white tips wear quite quickly in autumn whereas adults can remain relatively fresh throughout the winter.


Photo 25. 1Y (juv) primaries showing how the white tips become quite worn and chipped by early autumn. Sometimes the white tips wear away almost completely.

Photo 26. Adult primaries still showing fresh white tips with no wear and this photo was taken a month after the juvenile above..The outer 2 primaries have a slightly lighter brownish black ground colour compared to the rest of the primaries. This is normal in both adults and juveniles and is a result of these feathers taking more of the stress when the birds are in flight. The feathers on the leading edge cut through the air and are subject to more wear, tear and bleaching as a result. The large feather of the alula fades more quickly for the same reason and explains the difference with the small feather of the alula shown in photo 10 above.
Even though I have taken a lot of photographs it is really difficult to show some of the features well as they are quite subtle. The contrast between some feathers is fairly easy to see in good light when you can keep tilting the bird to catch the light but is much more difficult to photograph. I just hope some of you find this of interest and useful as a reference.

UPDATE 01/02/14
I caught a few Goldfinches on 30/01/14 that included another known adult (ringed in 2012) along with an unringed adult and some first winter birds. This allowed me to make a direct comparisons of the relative wear of the known adult, new adult and juveniles and to see if the differences in wear were still as marked as they had been. I took the usual range of photographs and present a few reference images below.The difference in wear is slightly greater to that seen in the late autumn/early winter in these individuals with the juvenile having lost more of its white primary tips to the point where they have almost disappeared on some feathers. The adult primary tips remain complete and very fresh in comparison and this was equally true for the new adult.


Photo 27. Juv top and adult below. The difference in wear is quite marked with the white tips of the juvenile having almost completely worn away. The adult feathers still look very fresh in comparison and show no abrasion or chips. The outer 2 or 3 primaries of both birds show the more brownish black background colour discussed in the original post above (see photo 26)


Photo 28. This juv has replaced all of the greater coverts (0 OGCs) . In this individual you can see some contrast between the glossy black part of the new greater coverts and the old juv primary coverts, and alula but be aware some adults can look like this as shown and discussed above.

Photo 29. There is little or no contrast between the black part of the greater coverts and primary coverts in this known adult. However the large feather of the alula stands out as being much paler. This is just because of the additional wear and tear that feather takes in the course of normal flight and is not a case of that being an older unmoulted feather. There are no 'moult limits' in this wing.
Photo 30. Juv tail. This bird has replaced all but the 3rd and 4th outermost tail feathers. The difference in wear and shape is there to be seen but they are not huge even this far on in the winter. You do need to check every tail feather on every bird.

Photo 31. Known adult tail. All the feathers are clearly of the same age with little or no signs of wear.
D130399 was also interesting in that I hadn't caught it in the usual way. This bird flew into a window and stunned itself on 03/11/12. I kept it in a bird bag for a short time afterwards and it seemed to recover quite quickly so I ringed it prior to release. It is nice to know that birds can fully recover from such impacts.

I will update this post again later in the year (ideally March or April) if I catch any suitable retraps/known age birds that show how the plumage wear progresses.

No comments:

Post a Comment