CROSSBILLS!!!

In the last week and a half I have done two sessions at Leith Hill which has probably seen the last of the Redpolls with just ten caught including one control and one retrap.  Whilst the first session produced no Siskins at all, the second produced 11 new, which were all 1st year males, and six retraps of which just one was female.  From this I can only imagine that the females are busy sitting on eggs and although fledglings have been seen elsewhere already none have been seen here yet.  Other catches new birds here included four Chiffchaffs, the first Blackcap, the first four Willow Warblers and a Brambling (below), but the highlight was 11 Crossbills.

Finally, after 16 months of watching them flying around the tree tops above my nets we have finally managed to catch Crossbills!  What a magnificent creature they are, even if they are a bit of a challenge with ageing and sexing.  Firstly, what species are they?  The three species of Crossbill that occur in Britain (Parrot, Scottish and Common) are all very tricky to tell apart as they are very similar so after a series of head and bill measurements were taken they were all within Common Crossbill, phew!  Then, what age are they, well because Crossbill can breed so early in the year (fledging as early as December or January)  normal rules don't necessarily apply because they can have two moults in one year.  If they have bred early then a first partial moult after breeding takes place by both juveniles and adults early on and the replacement feathers whether male or female will be greeny/yellow in colour.  Then in the late summer early autumn adults complete their full post breeding moult and juveniles complete their post juvenile moult with these feather colours being red for males and greeny-grey for females.  Sounds complicated but I hope this makes sense!  The following photos show some of this:

1st year juvenile Crossbill (3J):

Large amount of feathers around head replaced with new greeny/yellow ones, but streaky grey juvenile feathers still present also.

Rump still streaked with a few greeny/yellow feathers replaced above tail coverts, no unmoulted greater coverts and fresh looking flight feathers

Most body feathers replaced on underside with new greeny/yellow feathers but still a number of streaked juvenile feathers present.

1st year juvenile Crossbill (3):

This particularly yellow bird seems to be a more advanced juvenile than the previous bird in that it has undergone more of a partial moult.  Tiny flecks of juvenile plumage can just be seen on head, rump and undersides, but no moult in greater or median coverts and still fresh flight feathers.

A clear wing contrast between the particularly yellow 1st year bird and a 2nd year female.  Also note the bleaching of the tips of the 2nd year bird which shows that these feathers are a lot older than the unbleached 1st year.

2nd year female Crossbill (5F):

This was one of two birds that had a particularly orange overall plumage with the exception of the mantle and wing feathers which were green. The moult limit in the greater coverts showing contrast between six adult and four juvenile feathers gives away that this is a bird born in early 2011, whilst the highly developed brood patch shows it to be a female.

The rump in this photo is particularly orange in colour and contrasts completely with the green mantle.

2nd year female Crossbill (5F):

In contrast this is a more regular greeny/grey female, still showing the contrast in the greater coverts.

2nd year male Crossbill (5M):

A really good example of a bird that was born in very early 2011 having done a partial post-juvenile moult in the spring which is the greeny/yellow feathers on head and collar and then completed this moult in the autumn with the array of red feathers being a male, but still retaining some of the juvenile greater coverts.

Variation in feather colouring also shown in this photo of its rump and a few of the new greater coverts can be seen with a red edge rather than green. 

An interesting additional observation was that the mandibles of the cross bill didn't seem to follow a rule, in that some top mandibles crossed to the left while others to the right.

Other ringing over this period included a couple of mornings in my garden which produced 37 new birds including seven Goldfinch, seven Greenfinch, a Coal Tit (unusual here for this time of year), two Chaffinch and a Blackcap (below).

This week also saw my first nestling ringing with a nest of three Blackbird by my office (below).

Birds ringed:
Lesser Redpoll - 4
Redpoll sp. - 4
Goldfinch - 8
Brambling - 1
Blackcap - 2
Blue Tit - 17
Chaffinch - 3
Dunnock - 2
Great Tit - 4
Coal Tit - 1
Siskin - 11
Crossbill - 11
Blackbird - 3 nestlings
Song Thrush - 1
Chiffchaff - 4
Willow Warbler - 4
Long-tailed Tit - 1
Greenfinch - 7