Monday, 5 July 2010

"Northern Exposure", Crossbills in Northern Isles....Again !

For the past few weeks (since approx. early/mid June) Common Crossbills have been trickling in through Orkney, Shetland and North Ronaldsay. Readers may recall that last year there was a biggish influx of type 4E Common Crossbills to mainland Scotland ( and presumably UK). I picked up  birds in decent numbers in lower Deeside by early July, where they had not been present previously that Winter/Spring.

Okay, guys and gals in Orkney and Shetland, what call types are you getting this year ? It would be very interesting to know. Colleagues in Grampian Ringing Group had a ringing recovery of a Common Crossbill in April near Dufftown. This bird was ringed in September 2009 in lower Deeside so had moved Northwards somewhat in the six months since ringing. Was this a bird returning 'back' to where it had come from ? My instinct is 'no', it was possibly part of a nomadic post breeding flock that was seeking a decent cone crop. But the possibility remains, especially given the accepted view is that birds move south and westwards.

So if this years influx of Commons on the Northern Isles is giving 4E calls does this mean they are last year's birds going home ? Maybe and maybe not. Maybe, for the scant evidence cited above and 'not' because some 4E's may have remained in Fennoscandia where there was a localised food source and are only moving now after breeding ( there are juvs in the recent photos I have seen of birds on Shetland). This is this 'lag' effect I spoke of last year, and this would depend on how far from the East the birds were erupting. However, if the calls of this years irruption is different from 4E then at least it rules out the 2009 population returning or a new one of the same type irrupting. As I recall there were some 1A's and 1B's last year also, though in much smaller numbers than the 4E's.

4E Common Crossbill

The other intruiging possibility is that of small numbers of Crossbills trickling in during the winter months and early spring. I have had Common Crossbills at coastal sites in November and December and two flew over my garden this April ( there is no substancial viable food source near me and I am less than a mile from the coast). These may also have been birds moving Northward back up the coast. However, I would expect the legions of Vismiggers to have picked up such movements if they were happening with any regularity ?

If anyone wants to post comments please do - I have not completely disabled the comments but am unfortunately having to moderate them due to the chinese spamming that seems to be more and more prolific on blogger these days !


Dougie Preston said...

Looks like Shetland is getting 4E's again... well at least 2 anyway (inc the juv one)

Loxia Fan said...

Cheers for that Dougie !

Mmmmm "incoming" or "outgoing", that is the question ?

Perceived knowledge would suggest this is a new wave coming in, straglers from the last invasion now moving westwards from Fennoscandia ? I off to check the Falsterbo vismig sightings......

Loxia Fan said...

....and they don't start vismig obs there until 1st August !

Dougie Preston said...

And we might also be getting more 1B's again like last year, as one of the five birds I found yesterday was giving the same sonogram as last years Unst birds. This flock also included a couple of juv birds along with Male and Female... (family group?)

Loxia Fan said...

That is interesting Dougie. These are most likey Scandie birds coming in - possibly some of the birds stayed there and bred.

However, ringing studies in the 90's showed that trapped Common Crossbills in Deeside had high fat scores in the Spring indicative of birds that are about to migrate - whether locally or nationally is not known.

The fact that these are the same call types as last year's birds shows there is a lag effect - either birds coming in (most likely)or some birds going out a year later (less likely given a decent Larch and spruce crop here).

If there are lots of birds moving through the Scandie countries this autumn then this would possibly suggest a lag effect eg. last year pockets of birds 'settled'along the way from wherever they came from in the East - I don't necessarily subscribe to the 'lemming effect' notion that they ALL head South and West, though clearly many do.

I also have doubts about Crossbills traversing from mainland Scotland back across the North Sea - AFAIK there is no evidence(so far)of this, only birds from South West Europe apparently returning via the continental low countries.

I hope the guys on Orkney are sound recording as they are getting quite a lot of birds through.

Alastair said...

I will try to encourage a bit of recording here, I've been off South so haven't come across any xbills yet, watching the garden feeders avidly and listening out (whilst digging the foundations for the new greenhouse:-(

Loxia Fan said...

Cheers for that Alistair. You guys seem to be getting the crux of them and last year the recording in the Northern Isles provided useful clues !