Marsh Warbler at Stanford Reservoir, 7th June 2023

Chris Hubbard, our Sightings Officer, keeps a very close eye on the birds at Stanford, here is his account of one encounter with a very elusive species: 

As we moved into June, I became increasingly aware of a significant influx of Marsh Warblers into the UK. June is also a month when Icterine, Melodious or Blyth’s Reed can turn up and all are possible at an inland site with suitable habitat. As an avid patch birder, you should never rule anything out and events across the rest of the country are often early indicators of something good happening on the patch.

On the morning of the 7th June, I had already walked along the Leicestershire side of the reservoir and as I often do, decided to turn around and walk back to the dam to re-check the reedbed.

As I walked along the path adjacent to the reedbed, I picked up on a very distinctive and different song coming from hawthorns bordering the area. My initial reaction was Marsh Warbler but I knew I needed to rule out Icterine, Melodious and Blyth’s Reed. I was very familiar with Icterine Warbler having spent several hours listening to one at Rutland Water in June 2021. Even though Icterine mimics other birds it has a very distinctive ‘squeaky toy’ note which this bird didn’t have. However, I was less familiar with the song of Blyth’s Reed and Melodious although I had listened to them in the past in anticipation of an event such as this.

On returning later I was able to get much better recording and some brief views - my view on the bird’s identification hadn’t changed. I had already spoken with Mick Townsend (leader of Stanford Ringing Group) about releasing the news given that it was a very narrow track with breeding birds in the adjacent reedbed. I also thought the bird would be popular with local birders so needed to consult with Severn Trent about potentially allowing non permit holders on site. On the basis that I would be there to monitor, I released the news and this allowed birders ample time to visit and enjoy this very rare bird for the county. I last heard it sing at 20.50 and it wasn’t present the following day. 

Description
The bird remained incredibly elusive throughout. Overall, I had three brief views of the bird despite it singing from hawthorn only a few feet away. The combination of views were enough to confirm that the bird was an ‘Acrocephalus’ warbler. Crown and mantle were light grey-brown with off-white underparts. When I had slightly obscured views later in the day of the bird preening in the base of a willow, I felt that this off-white colour also looked tinged yellow / brown. The bird never sang from a high perch but remained either in hawthorn, cow parsley or the dog rose all bordering the reedbed. It seemed to do circuits between these positions during all of my observations (c.6 hours in total) but never gave a clear, unobscured view. It also fell silent for periods before starting to sing again from one of its favoured positions.

The song was the identification clincher. It is difficult to write down what a song sounded like but I have posted recordings on my Twitter feed and on the LROS Facebook page. It had very few pauses – very excitable made up of a number of elements of mimicry. I noted Blackbird alarm call, Great Tit, Song Thrush and House Sparrow in one section alone. Sometimes the song seemed quieter, but still excitable and quick. The speed of song, lack of clicking call between sections of the song and the array of mimicry ruled out Blyth’s Reed. Also, the combination of the song and the views confirming the bird as an ‘Acro’ ruled out Icterine and Melodious.

This is the sixth record for Stanford Reservoir, the previous records are summarised here:

17th June 1984 – ringed on the Leicestershire side
16th May 1989 – singing bird on the Northants side
7th June 2000 – ringed on the Leicestershire side
9th August 2018 – ringed on the Northants side
10th September 2020 – ringed on the Northants side

This is the ninth record for Leicestershire and Rutland and the first for 23 years.

Chris Hubbard

Images of a singing Marsh Warbler (reproduced with kind permission from Andrew C Sims) taken around the same time of year at Chapel Six Marshes, Lincs.