Yellow-browed warbler on Whiteknights Campus (Chris Foster)
We have a new addition to the campus bird list following the exciting discovery by David Flack from the Meteorology department of Berkshire’s ninth recorded yellow-browed warbler. He kindly sent me the following account of his find:
“I got into work for another Friday morning’s work preparing the slideshows for the department’s weather and climate discussion. A brief glance out of the window and I noticed a group of blue tits and a smaller bird in the birch tree outside my office window.
Initially I thought it was a goldcrest given the company it was keeping. I then thought I may as well check it with my binoculars just in case it was a firecrest. When I got the binoculars up I immediately got excited as it had two broad creamy wing bars and a creamy yellow supercillium and knew I was onto something special and a likely Berks rare bird and campus first.
My thoughts immediately went to yellow-browed Warbler or Pallas’s warbler, and I knew I had to get a view of the top of the head to confirm my suspicions. I briefly lost it for a second or two but moving further along my office I was able to get opposite the tree and it eventually showed itself slightly below the window at a distance of about 2m and there was clearly no crown stripe, leading to the conclusion of Yellow Browed Warbler.
I went to get some paper to make some field notes and by the time I had finished the warbler had come even closer to the window and was only about six feet away, giving clear views away from the leaves and of the distinguishing features without the need for binoculars. There was someone else in my office at the time and I asked them to look at the bird just to make sure I wasn’t dreaming and it was really there.
This is when I put out the news and just as I was doing so it disappeared; I noticed it was heading towards the lake so added that onto the end of my report as due to work I was busy all morning.
It took a while for the reality of what had just happened to sink in but as I was working I had decided that I was going to try and refind it at lunch. “
Yellow-browed warbler (Phylloscopus inornatus) is an attractive, pale green coloured leaf warbler (in the same genus as chiffchaffs) with a double yellow wing bar and a bright yellow eyebrow, as its name suggests. It predominately breeds in Siberia and usually winters in Southeast Asia. Each autumn a few hundred are seen in the UK, thousands of miles off their usual course. This was thought to be wholly due to the phenomenon of reverse migration or misorientation, whereby a bird has somehow got one of its navigation aids switched and sets off at 180 degrees to its intended route.
However, the wide geographic spread of records up and down the east Atlantic coast and the increasing occurrence of P. inornatus in our region has led to speculation that a small proportion of the population has an established southwesterly migration to as yet unkown wintering grounds in Western Europe or North Africa, perhaps arising in tandem with the westward expansion of the breeding population this side of the Ural mountains. Every year a very few yellow-browed warblers do winter in Britain, and last winter a Pallas’s leaf warbler (a scarcer, closely related species) passed the winter in Berkshire at Moor Green Lakes local nature reserve. But the numbers wintering must be very small, as there are surprisingly few spring records even after allowing for the fact that spring migration tends to be both more rapid and more direct than autumn migration, which involves a large number of inexperienced juvenile birds. A survey of records in Iberia suggests that much of the autumn influx of both species into Western Europe may in fact be due to exploratory migration by juveniles, which migrate back to Asia later in the autumn.
The first ever record of yellow-browed warbler in Berkshire was in the winter of 1986 to 1987, when one spent over a month residing in a Thatcham garden. The county’s birdwatchers had to wait 17 years for another, at Theale in 2003, but since then they have occurred with increasing frequency each autumn, matching the growth in numbers passing through nationally, culminating in one bird trapped and ringed in Hungerford on 2nd October and finally Friday’s Whiteknights bird. They very often mix with tit flocks – Friday’s was in the company of blue tits for most of its brief stay – and can evidently turn up almost anywhere, so it’s worth having a close look at any small, greenish birds mixed in with tits and listening for the yellow-browed warbler’s distinctive, piercing call throughout the autumn.
Listen: Yellow-browed warbler songs and calls at Xeno-canto, BBC Radio 4 Tweet of the Day