A Field Notebook: Singing Icterine warbler on a BBS

Photos: Icterine warbler, © WC Aspin.

A remarkable Breeding Bird Survey this morning, I found a singing male icterine warbler in a hedge in eastern England.

I was on site at 4:10am and began my trek around the fields. Just the usual, depressingly familiar, big empty fields and largely silent hedgerows. Then I came to a stream, lined with bushes and adjacent marshy ground. This looked more promising and I followed a track along the stream until I came to a pond with tall trees. Suddenly I heard a song which I didn't recognise. My first thought was marsh warbler and I tried a bit of playback which the bird seemed to respond to, but I wasn't convinced, something didn't seem right. Thankfully I decided to record the song on my phone.

Over the next hour I had fleeting glimpses of what seemed to be a largish yellow looking warbler flitting around the bushes or occasionally flying but though it was vocal, it was very skulking. Finally I nailed it with two brief but excellent views of a singing, lemon yellow bird with pale lores and a pale bill. But this was no marsh warbler, it looked more like icterine! Then it was gone.

I had very limited experience of hearing marsh warbler in song and I'd never heard singing icterine previously, so I needed a second opinion. I had no photos but I had recorded it's song which I sent off to some colleagues. After a short while they got back to me. There was no doubt about it, it was a singing icterine warbler.

The species is at best a very rare breeding bird in the UK, with probably less than five singing males annually and the majority of these are just singing passage birds at coastal localities or in the extremities of the country, especially Shetland. To find a singing bird at an inland site with such good looking habitat was very exciting.

The habitat certainly looks good for breeding icterine, an unmanaged species rich hedge along a stream with an adjacent pond, scattered willow trees and sunny marshy glades, set in the middle of a large area of arable farmland at least 30 miles from the coast. The bird was clearly on territory flying around a circuit singing in favoured bushes but always returning to one bush in particular, where it spent the majority of it's time. Apart from brief flight views as it moved around, it was very difficult to see, usually immediately disappearing into whichever bush or tree it landed.

The song was energetic, loud and variable but always seemed to start with a starling like 'shrr, shrr, shrr' and include a nasal shrill 'chi chi chi chi voooi'. There was much mimicry and repetition in the song, recalling song thrush, and given the fact that there were at least a couple of song thrushes singing in the same area, I wasn't sure if the bird was actually mimicking them or whether this was just part of it's normal song, but whatever the truth, it all added to the mix and at times created some uncertainty as to exactly which bird was singing. It was an altogether magical experience which at times seemed quite surreal, to be standing in an oasis in the middle of relatively barren farmland listening to icterine warbler singing in amongst all of the other bird song which included blackcap, lesser whitethroat, blackbirds, wrens and robins and with hobby and red kites occasionally hunting overhead.

It all looks very promising, except perhaps there is one vital element missing - a female. I certainly didn't see or hear her, but hopefully she is there hidden somewhere. The male was difficult enough to see when in full song, so I would imagine that a silent female would be all but impossible.

Obviously I'm not going to reveal exactly where this is, quite apart from the fact it's on private land, it's also a potentially extremely rare breeding bird. Best I can say is it's at a site east of York. I've got several more surveys planned to this site and it will be interesting to see if the bird is still present.

Edit 30/05/2024: This morning I was joined by a colleague, Bill Aspin and fortunately his transect route also went past this same area so we arranged to meet up. The bird was in full song again and showed a lot better, though still difficult, and he was able to fire off the photos at the top of this post.

Edit 06/06/2024: the icterine warbler was still present this morning and singing lustily. I had my best views so far of the bird as it moved around its territory, such a beautiful bird, for the first time I actually noticed the pale panel in the wing and the lemon yellow on it's underparts really stood out today. I don't know whether prolonged singing indicates the presence of a female or just an increasingly desperate and lonely male but the fact that it's been here for a minimum of nine days now is surely at least encouraging! Trouble is, I'm not sure how we will ever prove the presence of a female without seeing the offspring, but just enjoy it while I can I suppose.

Edit 07/06/2024: Icterine warbler heard singing briefly by a colleague.

Edit 18/06/2024: First visit to the site since 07/06 and colleague reports no sign of icterine during an early evening visit.

Edit 26/06/2024: First visit to the site since 18/06, no sign of icterine at dawn for me. Presumably gone, or perhaps just stopped singing.