A Yellow-browed Warbler at Frampton-on -Severn and comments on reverse migration

Every year a small and variable number of Yellow-browed Warblers attempt to over-winter in the UK. This represents a very interesting example of bird vagrancy. Its nearest breeding range is some 5,000 kilometres away and the vast majority winter in southeast Asia.  A small number, however, exhibit a phenomena known as reverse migration and head off 180 degrees in the wrong direction and end up in the UK. The current theory is that this is due to a genetic error causing  them to get magnetic north and south mixed up, see here for a much more detailed account of the causes of bird vagrancy. There is a possibility that having a small fraction of the population reverse migrate has an evolutionary advantage in that, if the habitat and climate is convivial, it would help establish a second independent population. To the best of my knowledge the Yellow-browed Warbler has never attempted to breed in the UK so these reverse migrators must either not survive our harsh winters or successfully migrate back to their Asian breeding grounds in the spring.

 

The Warbler was located some 30 miles from home in the very pleasant park at Frampton-on-Severn. It had been faithful to a particular spot on the ground under a stand of 3 limes where it had been foraging for insects on the ground. This is a bird I would expect to see every year with Shetland being a particular hot spot for them. I have, however, never seen a bird exhibiting this behaviour of foraging on the ground. They are usually in the treetops making viewing somewhat problematic and often leading to a sore neck. This hence provided a rather unique bird watching and photography experience.

 

The bird was not present when I arrived on a cold damp and rather miserable winter morning but after about 30 minutes I spotted it fly out of a bramble bush onto the ground. It then flew again and landed underneath the limes. It took another 30 minutes or so to find it creeping through the grass where it was somewhat obscured. It was feeding in the normal hyperactive manner of a Phylloscopus warbler, very restless and never still as it foraged around the grass and leaves continuous feasting on invertebrates: there was clearly plenty of food to sustain it. It is a small, green warbler similar in size to a goldcrest featuring  the distinctive yellow supercilium or eyebrow which gives it its name.

 

I was well prepared for the cold with thermals and lots of layers but the cold northerly wind slowly seeped into my bones.  So I made a break for Slimbridge just down the road for a spot of lunch and winter bird watching with the intention of returning mid-afternoon to try and get better photos.

 

After a rather horrible soup reporting to be vegetable in the café I made my way slowly along the Rushy side hides where there were literally thousands of overwintering wildfowl and waders. The birds far exceeded the number of visitors reduced no doubt by the cold winter weather. I didn’t take any photos, rather I decided to spend a layback 2 hours just bird watching the Slimbridge winter avian spectacle at its best. In terms of scarcer birds the highlights were the overwintering Little Stint and juvenile Spoonbill and a small flock of Russian White-fronted Geese.

 

I returned to Frampton with 90 minutes or so of daylight left to find the Warbler showing very well under the Limes. It really was most confiding totally ignoring both the small number of watchers and walkers who passed by. At one point it flew directly towards me and landed no further than one meter from my tripod, much too close for me to focus on it. I picked up my tripod and slowly shuffled back thinking I would disturb it but it continued to ignore me with complete and utter disdain! 

 

As the sun started to set I left for home, so thankful that I went back for a second afternoon encounter with my hyperactive little winter gem.

 

 

 Footnote – my blogs are posted with sometimes rather imaginative spelling and grammar due to my extreme dyslexia!