A Tale of Two Willow Wrens

Like Dickens' novel, A Tale of Two Cities, this story is also one of contrasts; between birds, places and ways of studying natural history. It was another English literary giant, the 18^th century natural historian Gilbert White - and grandfather of biological recording - who first distinguished, on the basis of their songs, not two but three distinct warblers amongst a group previously thought of as a single species - the Willow Wren; these were Chiffchaff, Willow Warbler and Wood Warbler.[1]

Since Gilbert White first separated the three species, Wood Warlber has probably declined to a much greater extent than the other two. It now has a westerly distribution in the UK and an encounter with Wood Warbler is a red-letter day for most naturalists. Despite the early confusion they are reasonably easily identified by sight, being larger, brighter and yellower than both Chiffchaff and Willow Warbler. I have rarely seen Wood Warbler at home in Lancashire, although this year I was astonished to find a pair in a local woodland which subsequently bred. (Another local naturalist found a second breeding pair - a wonderful turn of events that we hope will be repeated in future years.)

The jokey epithet of Wiffwaff is given by birders to a warlber which could be either Chiffchaff or Willow Warbler and is testament to the fact that these two species are very similar in appearance and still cause confusion from time to time. There are quite reliable differences, but if a good enough view isn't forthcoming, they are difficult to tell apart by sight. Fortunately there is one excellent way to distinguish them - their songs which, although equally delightful, are quite distinct and easily identified, as Gilbert White first noted. (The beautiful song of the Wood Warbler is also very characteristic.)

The Swallow and the Cuckoo may be the iconic harbingers of the British summer, but it's the migrant warblers that lend so much rich texture to our springtime soundscape. In March I anticipate their arrival with child-like excitement. Chiffchaffs, Willow Warblers, Blackcaps, Whitehroats, Garden Warblers - each arrives from Africa singing songs not heard for six months or more, dispensing joy freely to anyone who cares to listen.

Weekly totals of my Chiffchaff records for 2011-2013.

In 2010 I started making biological records using a GPS datalogger with a voice recording facility (effectively a GPS-enabled dictaphone).[5] It meant that I could make a record of a bird in as much time as it took me to press a button and say "Willow Warbler!". Like most biological recorders, I'm somewhat eccentric about what I record and when I started carrying this device about with me, I found it hard to let any encounter with a summer migrant pass without making a record. Of course the odd one slips by now and again - it's awkward to interrupt a meeting at work to make a record of a singing Chiffchaff - but I get a good proportion of them.

One consequence of all this recording is that I can look back and see a more or less complete picture of my personal encounters with these birds over the course of the summer. The incredibly cold March of 2013 delayed the arrival of many  summer migrants; an event comprehensively documented by records submitted to the BTO by thousands of recorders up and down the country.[2] But there's something about seeing that same phenomenon reflected in your own personal observations that really brings it home.

In February 2013 I started working for the Field Studies Council at Preston Montford in Shropshire (just north-west of Shrewsbury), although I continue to live in Horwich, Lancashire and split my time fairly evenly between the two.Whereas in 2011 and 2012 most of my summer migrant records were made in Lancashire, in 2013 I made good numbers in both counties. In Lancashire, most of my summer migrant records are made when I walk with my dog through countryside on the edge of the West Pennine Moors. In Shropshire, most of them are made around the field centre where I work and at a nearby site where I frequently camp (both adjacent to the River Severn).

Weekly totals of my Willow Warbler and Chiffchaff records for Preston Montford, Shropshire in 2013.
 (Chiffchaff photo thanks to Lip Kee.)

Chiffchaff and Willow Warbler frequently occur together and both are ground-nesters favouring open habitats with scrub and scattered trees. Chiffchaff tend to prefer, or tolerate, more mature stands of trees than Willow Warbler, but there is considerable overlap. The countryside differs between the two places where I recorded these birds in 2013, with that in Lancashire being more upland in character, but each of them offers plenty of suitable habitat, on the face of it, for both Willow Warbler and Chiffchaff.

Weekly totals of my Willow Warbler and Chiffchaff records for Horwich, Lancashire in 2013.  
(Willow Warbler photo thanks to Andreas Trepte, www.photo-natur.de.)

Given the apparent suitability of the habitat in both places, the pattern of my encounters with Willow Warbler and Chiffchaff in each show striking differences. Although I recorded Willow Warblers in Shropshire as they arrived, these moved on quickly. In Lancashire I heard them in good numbers, just as in previous years, and it was easy to count 10 or more birds during a walk of an hour or two. In Shropshire I only made 8 Willow Warbler records over the entire summer - and all of those, I believe, were passing through. Although I recorded more Chiffchaffs in Shropshire than in Lancashire, I had good numbers in both counties.

I remember a visit to the headquarters of the BTO in Norfolk in 2012 and recall how staff bemoaned the scarcity of Willow Warbler there, getting quite excited when one was heard on the adjacent reserve! To be honest I didn't think much of it because in Lancashire I had just as many Willow Warblers as ever. But, at that time, the BTO researchers were seeing the preliminary results of Bird Atlas 2007-11- a project collating the observations of over 40,000 volunteers (of which I was one!) - and they saw a bigger picture emerging of a massive decline of Willow Warblers in the south of England.[3][4]

Willow Warbler change (with permission of BTO)

Still it rocked me when I saw that decline for myself as I compared Shropshire and Lancashire this summer. Part of it was because I hadn't imagined that the loss would have been as dramatically clear as far north as Shropshire, but there's no doubt that the impact on me was greater because I witnessed the difference through my own observations.

We don't yet know the reasons for the decline of Willow Warblers in the south of the country compared to the north - in fact it is a pattern that the new atlas shows is reflected by several other woodland and farmland birds. Climate change may be playing a part - either in the summer or wintering quarters - as may other anthropogenic factors, but at the moment we are speculating.

I wonder what Gilbert White would have made of it all? As a great advocate of learning through direct observation he would have approved of my efforts and he would surely have been astonished at the power of the massive collaborative effort for the BTO's Atlas project. But what of the decline of the Willow Warbler and the possible causes of it? Perhaps he would, like many of us, have felt simultaneously excited and depressed.

Dickens' words, penned between White's time and our own, seem particularly apt: "It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness". We have to hope that our ingenuity in tracking changes in the natural world around us does not end up merely as a means of documenting our own foolishness. And if you are lucky enough to live in a part of the country where you can still hear Willow Warblers singing in the summer, then enjoy them; a summer may soon come when they are no more than a memory to your part of the world.

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1 See a short biography of Gilbert White here:http://www.nhm.ac.uk/nature-online/science-of-natural-history/biographies/gilbert-white/ [back]
2 A news item from the BTO's Birdtrack project documenting the slow start to the Spring of 2013:http://www.bto.org/volunteer-surveys/birdtrack/news-archive/2013-03/slow-start-spring [back]
3 A preview of the Willow Warbler's story from the BTO Atlas 2007-11: http://www.bto.org/about-birds/bird-of-month/willow-warbler [back]
4 The BTO Atlas 2007-11: http://www.bto.org/shop/bird-atlas [back]
5 The Gilbert 21 project: http://www.gilbert21.org.uk/ [back]

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