04 February 2012

It's all about the sewage

It’s well known that wintering Chiffchaffs have a great affinity with the southwest, with Devon and Cornwall home to an unknown, but undoubtedly large, proportion of the UK wintering population. Looking back at just the last five winters (December to February in each of 2006-07 to 2010-11), we hold electronic ringing records of 918 Chiffchaffs, with no fewer than 244 ringed in Devon and 187 in Cornwall. Over these years, the highest winter total was 86 birds ringed in Devon in 2008-09.

Despite this winter being relatively mild, we’ve been having great success in catching wintering Chiffchaffs at several sites in Cornwall, thanks largely to the support of South West Water in allowing us access to works areas. Since the start of the year, we’ve ringed 105 Chiffchaffs at just three sewage works in Cornwall, including 41 on one day alone. This compares well to previous years, with the highest winter total nationally being 265 in 2009-10.

The racial identity of these birds is also interesting, with a small proportion being of northern races: either abietinus or tristis (Siberian Chiffchaff, above). Interestingly though, yesterday morning saw us catch a French-ringed bird, perhaps indicating an alternative origin of these wintering birds. There are just 13 previous records of French-ringed Chiffchaffs in the UK, of which three have been in Cornwall and two in Devon.

The sewage works sites are also important for various other wintering species, and yesterday’s catch also included two Firecrests and two Yellow-browed Warblers (below) in amongst the more expected 35 Chiffchaffs. The Yellow-broweds are of particular note, as of the 902 electronic ringing records we hold, just six have been in winter (five in December and one in January).

Thanks to Ashley Hugo for the tristis Chiff photo and Adam Hartley for the Yellow-broweds.


  1. http://grupodeanillamientolula.blogspot.com/2011/11/abietinus.html

    dear all
    why the picture is a tristis and it is not abietinus?
    In my opinion is a phy col abietinus because iit is more brown and tristis is a little white.
    In our blog you can see several photos to abietius.
    Best regards


  2. Are the sewage works reedbeds? Where do the birds live and feed? Most sewage works that I see have no habitat for chiffchaffs, just tanks.

  3. Most of the bird's we're catching have been feeding on insects around the large settling tanks. We catch them commuting between the tanks and bramble hedges alongside the works.

    As for the racial identity of these birds, genetic work done by Greg Conway at these sites a few years ago indicates that these birds are more likely to be tristis than abietinus and that the field (or in-hand) identification is far from clear. There's the additional problem of intergrades (fulvescens?) where even less is known. Also, many of these birds lacking yellow/green colours respond to song of Siberian Chiffchaff and not Common Chiffchaff.

  4. While most of us dread the site of sewerage waste, it is good to know that there are animals who benefit from this like that of the Chiffchaffs. The birds migrate to water sources as well as sewage work sites during winter and I do hope that they are not disturbed and they continue to come by in these areas every year.