Back in October 2016 I had one of the absolute highlights of my ringing career when I caught and ringed only the second ever Yellow-browed Warbler processed in Wiltshire, in the wildlife refuge at Lower Moor Farm. Whilst today does not equate with the importance of that catch for Wiltshire records, it is right up there with the best catches for me personally. More on that later.
With the weather forecast for today being for a low breeze and no April showers, I decided upon a visit to Lower Moor Farm. It started out very cold: -1oC. It started to warm up after 9:30 and by the time we started packing up just before midday it was T-shirt weather.
I was joined for the morning by Rosie and Anna. Rosie was working with a volunteer group at Blakehill Farm from 10:00, so would have to leave by 9:10 to get ready, and Anna was with me for the whole morning. We met up at 6:00 and set nets in the wildlife refuge area:
Jonny Cooper caught his first Willow Warbler of the year on the 30th March and his first Reed Warbler of 2023 on the 7th April, both at Wiltshire Wildlife Trust’s Langford Lakes reserve, so I thought I would have a look see what warblers might have arrived at our similar habitat in the north.
I put on lures for Chiffchaff, Willow Warbler, Blackcap and Whitethroat as they are only now arriving on these shores, whereas many of our resident species are already paired up and ready to breed (if they aren’t already: I have seen juvenile Collared Doves and Blackbird already this year). My expectation was not for a large catch: March and early April are always quiet times at my sites, but I was hoping for a few warblers today. We did start catching straight away and it became clear that Chiffchaff would form a significant part of our catch today.
So what unusual bird did I catch? At 8:30, in the 12 metre net at the far end of our net setup, were two Phylloscopus warblers: one was a Chiffchaff and the other dwarfed it. Its head was about 50% larger than that of the Chiffchaff. To my mind, it was a Willow Warbler on steroids. Looking at the bird, I thought it had to be a Wood Warbler. I ringed it and then set about confirming my initial thoughts, using the biometric and plumage data from our two Passerine bibles: Svensson’s Identification Guide to European Passerines and Demongin’s Identification Guide to Birds in the Hand. From those I could compare what I had measured and could see on the bird with the parameters for both Willow Warbler and Wood Warbler.
This is my reasoning, with apologies for the technical jargon. When processed, the overall features of this bird say Wood Warbler: 74mm wing length, 56mm tail length & 10.6g weight. The measured wing length is beyond the extreme given for Willow Warbler, but the tail length and weight were within the given ranges for both species. According to both Demongin & Svensson for a Wood Warbler: wing length range = 70 to 81mm. Demongin gives a tail length range of 42 to 56mm and a weight range of 8 to 12g. However, comparing this bird with what they say for Willow Warbler: wing length: 60 to 71mm; tail length 42 to 56.5mm; weight is 7 to 12g. The wing length was the key diagnostic differentiator. The only thing that bothered me was that the colouration of the wings and back were duller than I expect for that species, not the bright olive green you see in every field guide. The throat isn’t bright yellow but the belly is entirely white, with no yellow streaking.
It was such a big chunky bird for a Phylloscopus. It was certainly greener than the photo shows (strong sunlight this morning), particularly the head colouration.
Wing point on Wood Warbler is 3, on Willow Warbler 3(4), P2 = 4 or 4/5 for Wood Warbler and P2 = 5/6 or 6 for the Willow Warbler. P2 on this bird = P5.
Although I have seen a reasonable number, both on breeding grounds in the Forest of Dean and on passage in a number of places, I have never held or seen one in the hand. That is not too surprising: the last Wood Warbler ringed in Wiltshire was back in 2016. So, before committing myself to a firm diagnosis of Wood Warbler and confirming the entry in the BTO database, I passed the details of the bird to my former trainer, Dr Ian Grier, and a former, long-serving, bird recorder for Wiltshire, Rob Turner, for their opinions. They also have over 80 years ringing experience between them and their depth of knowledge is exceptional. Ian confirmed by return that he would have no qualms about confirming it as a Wood Warbler, saying “The wing formula would have clinched it, with a noticeable long P2. The undertail coverts are white. The primary projection looks at least equal to tertial length. Aberrant brown and white colouration is well documented”.
If anybody has a different view on the identification of this bird, please don’t hesitate to contact me via the feedback system with your reasons.
The list for the session was: Blue Tit 1; Great Tit 1(3); Long-tailed Tit (2); Wren 1(1); Dunnock (3); Robin (1); Cetti’s Warbler (1); Blackcap 2; Wood Warbler 1; Chiffchaff 7(1); Goldcrest 1. Totals: 14 birds ringed from 7 species and 12 birds retrapped from 7 species, making 26 birds processed from 11 species.
Amongst the Chiffchaffs caught this morning was this punky little beast:
He has clearly been eating from a very sticky source to give him his pollen horn.
The only downside to this morning’s session was a female Bullfinch that we couldn’t ring. It was developing the warty excrescences on its legs caused by Fringilla papillomavirus.
It was a very pleasant morning, with lots of positive interaction with the general public, including a surprise reacquainting with Rob Werran and his partner. Rob’s a really nice bloke and came along for a few ringing sessions, but his work schedule just didn’t allow for him to keep at it.
As mentioned, we closed the nets by midday, took down and were away soon after 12:30.