Back to Woolston (6 July 2003)
On Friday 4th and Saturday 5th July I opened up my traditional netting site at the east side of no.3 bed at Woolston, ably assisted by Michael Miles. This is my 24th autumn of ringing there, but the first since I got my digital camera, so I was photographing lots of birds.
This always has been a good spot for moulting birds, especially Willow Warblers Phylloscopus trochilus.
They moult incredibly fast, and this male was actively moulting all of its tail, all three tertials, five primaries, two secondaries and numerous body feathers and coverts.
Remembering the standard moult score system of 0=old; 1=in pin; 2=up to one-third grown; 3=one-third to two-thirds grown; 4=two-thirds to fully-grown; and 5=new fully-grown feather, I would code this one as (starting with the tertials and moving outwards) 2 2 2 | 0 0 0 0 1 2 | 5 4 4 3 2 1 0 0 0 0. All twelve tail feathers were at stage 2. There must be a really good food resource for them to be able to put all of that energy into growing so many new feathers, and then, uniquely among western Palaearctic birds, they do it all again in Africa! The juveniles, like the one below, also moult during winter in Africa.
Adult Sedge Warblers Acrocephalus schoenobaenus, by contrast, migrate to Africa in the autumn before starting their moult. So, at this time of year, adult plumage is moderately worn (on the left in the photo below) while that of juveniles is pristine (below, right). Well, actually, this one is not quite perfect but it was only while sorting through the images that I realised that the juvenile bird has its smallest tertial on the left wing missing.
To remind us that it is still the heart of the breeding season for some species, we caught a '1J' - 'fledged, but flying so weakly that it is obviously incapable of having flown far from the nest' - Sedge Warbler, along with three 1J Reed Warblers Acrocephalus scirpaceus, two of which were caught by hand. These were all at the same time and I suspect that the similar food-begging calls of the two species attracted each other. Note that all feathers (wing and tail) were growing simultaneously, and they have an obvious gape-flange. Their muscles are not fully developed and they tend to droop their wings, which is why my finger is gently pushing the Sedge Warbler's wing into a more 'natural' shape!
Not all ageing is as easy as that, however, and we had a couple of interesting 'adult' male Blackcaps Sylvia atricapilla, neither of which had started their moult yet, suggesting that they may have females attempting second-broods somewhere. Both birds could be aged more precisely than just '4' ('adult', hatched before this year), by looking carefully at the moult limits in the wing coverts. The first (on the left, below) had nice, clean, grey-edged greater coverts, carpal covert, alula feathers and its primary coverts were greyish and rounded in shape. At first, I was confused by what I thought was contrast between the middle and large feathers of the alula, but realised after consulting Jenni and Winkler (Moult and Ageing of European Passerines, 1994) that this is what they look like. All of this goes to make it a 'full adult', Euring age code 6, hatched in 2001 or earlier.
The second male Blackcap (on the right, above) is a '5' (hatched in 2002) that had undergone a less extensive post-juvenile (=pre-basic) moult last autumn than the 'standard'. Most Blackcap juveniles moult all of their greater coverts in their first autumn, but this one has retained two old greater coverts, as well as the carpal covert and all three alula feathers. Its primary coverts are narrow and frayed, brownish-edged, clearly different from those of the bird aged '6'. All of these unmoulted feathers are now about one year old and have been to Africa and back (or at least the Mediterranean), explaining some of their wear, but the crucial point is that they are still the feathers that the bird grew in the nest and they are looser in texture and weaker than the feathers grown later: this explains the differential wear.
With the bird in the hand, some magnification often helps to see these subtle characters, as well as good light being needed. In case you don't believe me, or just have difficulty in seeing the contrast, one of the joys of digital images is that you can play with them on the computer - not much use for ageing the bird in the field, but useful for 'getting your eye in'. Using the photo editing software to enhance the contrast substantially produces the image below:
Finally, just to show that you never know what might happen with mist-nets, as I was taking down one net an adult male Moorhen Gallinula chloropus flew in. This is another of the species where the eyes are brownish in young birds but become redder with age.