October 8th   Leave a comment

At last, the annual Crail yellow-browed warbler festival has really got going. The winds were easterly over the weekend coincident with some very heavy rain. The perfect early October recipe for yellow-brows. I found at least eight this morning from Balcomie to Fife Ness to Kilminning. At one point I was surrounded by four or five at the entrance to Kilminning. They were showing themselves as well, at least by late morning. Little striped jewels of green and white and yellow seemingly everywhere. Perhaps not quite the 200+ they have on Shetland and indeed not even the best we have had in Crail (30+ in the same area as this morning in one year), but a great day nonetheless. On days like today there is always the feeling that the next bird you look at will be that heart stopping extreme rarity.

Yellow-browed warbler

Yellow-browed warbler

Yellow-browed warblers have been becoming increasingly common in the UK over the last few decades. They are an odd species to become more common because they winter in south-east Asia (Vietnam & Cambodia for example). Other species that have a similar breeding range (Siberia) and the same wintering range are only extreme rarities to Britain with one or two birds occurring every year. But with yellow-brows there are clearly thousands passing through the UK now every autumn. I think we are watching a new migration route developing as we saw with blackcaps. 40 years ago blackcaps shifted their migration from wintering in southern Europe to the UK. When I was a boy, a wintering blackcap was a great sighting, now they are a common wintering species, at least in England, and a very common bird table visitor. Young migrants head off to the wintering grounds with a fairly vague and variable genetic program, and weather and chance can soon play havoc with their final destination. With blackcaps, the few random juveniles that ended up in the UK in the 1970s by mistake started to survive better than those that went further to Southern Europe – probably because of global warming and our loss of really cold weather in winter. They returned to Central Europe to breed earlier than the Southern European birds to seal their advantage. As adults, they returned to the UK each winter (winter site fidelity is a common trait in migrants), sticking to the route and wintering ground that worked for them (better the devil you know!) and that allowed them to survive so far. Over the years, those individuals with a greater genetic propensity to go east to Britain rather than south to the Mediterranean have produced more surviving offspring, eventually shifting the whole population’s migration route. And so back to yellow-browed warblers, who seem to be doing the same thing. There must now be a population of yellow-brows wintering in West Africa like chiff-chaffs: only a few actually winter in the UK and they are only very rarely recorded in Iberia so they must keep going south after Crail. They have started to be recorded on the west coast of West Africa, and I think somewhere in Senegal or Guinea there must be patches of forest where they occur all winter. There are few birders in Africa and if yellow-brows stay high up in the canopy of the rainforest and don’t call much, ten thousand will disappear without any trace. It will be interesting to see whether this is true over the next few decades: sooner or later they will be become too widespread in Africa to escape notice. If it is true then another question arises: how can there be an advantage for yellow-brows to travel four times the distance to winter in Africa from Siberia compared to the relatively short jaunt down to south-east Asia?

Although there were lots of yellow-brows, other migrants were scarce. I saw a few chiff-chaffs in the sycamores along the airfield road and a single swallow high over a stubble field. There were barnacle geese coming in all day today in ragged flocks. They seem to be much more volatile in their flocks compared to pink-footed geese, forming constantly shifting bunches and only ever ragged short-lived Vs. Pink-feet look much more pedestrian as they arrive. The frantic yapping of the barnacle geese adds to their slightly panicky air as they pass by.

A typically ragged flock of barnacle geese arriving at Fife Ness

A typically ragged flock of barnacle geese arriving at Fife Ness

Posted October 8, 2015 by wildcrail in Sightings

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