Sibe Chiff overload at the sewage works

The middle of January 2022 saw the first spell of cold, calm weather, perfect to start our winter ringing at our local sewage treatment works (STWs). These sites are a haven for insects in the cold weather and where there are insects there are always going to be birds. In winter, the resident wagtails, Wrens and Robins are joined by large numnbers of Chiffchaffs, including Siberian 'tristis' Chiffchaffs, possibly from as far east as the Urals. Once considered a rarity in the UK, it's now become more apparent how frequent they are, especially in the far southwest.

Over the week of cold weather we managed to ring at four of our regular sites, all of which produced plenty of birds. We've ringed at these sites for several years, so recatching birds from previous winters is always interesting and it's rare to see a bird ringed at one site moving to a different one in a subsequent winter. In fact one of the birds recaught at Constantine had been ringed there five years previously, in January 2017! We do also catch birds from elsewhere which again gives us an insight into where these winter birds come from.

The table below shows the total number of Chiffs caught at the sites over the week, including new birds and those already ringed:

	Chiffchaff	Siberian Chiffchaff
Gwennap STW	44	7
Brew STW	39	12
Ponsanooth STW	31	2
Constantine STW	21	-
TOTAL	135	21

 

It's fascinating to see how the proportion of 'tristis' birds varies across the sites, with almost a quarter of birds caught at Brew, down to none at Constantine. This may be due to the surrounding habitat to some degree, as Constantine is very much an inland wooded valley, whereas Brew sits right down near Lands End on a scrubby hill. What's also interesting at Brew STW is that it sits at the top of the Nanjizal valley, where large numbers of Chiffs are ringed on autumn migration. Some of these stay for the winter, so it's interesting to look at when these birds first arrived in the valley. The Nanjizal Chiffs recaught at Brew this week were ringed in February 2020, October 2020, November 2020, and from 2021, on 22nd September (a surprisingly early date), 10th October, 5th and 11th November. As for the 'tristis' Chiffs, they were all ringed much later in the autumn in November 2021, on 18th, 20th and 24th. Some Nanjizal-ringed birds do also move through and winter elsewhere, with birds ringed on 25th October and 11th November recaught at Ponsanooth (44km), and a bird ringed on 6th November recaught at Gwennap (43km).

 

As for birds from further afield, we saw just one of these, with a Chiff ringed on Hartlepool Headland on 19th October recaught at Gwennap, 565km as the Chiff flies.

We're back to mild, wet weather now so fingers crossed for some more cold settled weather and we can get back to the works and see what we missed this week!