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FEBRUARY 2003 continued....
ARTICLES
Lee Valley Wintering Bittern Research Project
For some years the Rye Meads Ringing Group has been developing a project to study the precise requirements of wintering Bitterns in the Lee Valley. As between 5 and 10% of Britain's wintering Bitterns now spend the winter in the Lee Valley there is clearly something they like!
The project has been funded by the Lee Valley Regional Park Authority and Thames Water Utilities, and this enabled me to start the six-month contract in October 2002.
The first Bittern arrived in the Valley on 8 October and traditional sites were gradually occupied with new birds continuing to arrive up to the end of November, by which time eight had been located. I spent most days checking reed-beds, noting the characteristics of those occupied by Bitterns, and watching for birds at dawn and dusk at likely roost sites. Enjoyable days have been spent in the Lee Valley Park's Bittern Watch-point, noting every aspect of their life, including their (often massive) daily intake of fish.
Bitterns are very difficult to study due to the reed-bed habitat they prefer, and one aspect of the project was to try and find out how far individual Bitterns move about the Valley in the course of a winter. Are we over-counting them? Is a Bittern a seen at Amwell one day, then in the Cheshunt gravel pits the day after?
To answer this question I planned to catch a Bittern, using nets, and fit it with a radio transmitter (tag), and track it around the Valley. Initially I thought the best site for this was Rye Meads, the area with which I am most familiar: if not there, then possibly at Amwell. At both sites Bitterns were present, but very difficult to locate (what they needed was radio tags!).
In the event, the successful trapping of a Bittern was finally achieved at the Pochard Hide reed-bed in the North Metropolitan Police Pit at Cheshunt on 16 January 2003. A large mesh mistnet was erected before dawn in a corner of the reedbed frequented by a Bittern, and at 0850 the Bittern walked into it, entangling itself on the backward facing spikes in the palate of the upper mandible. After months of early mornings, wet feet, self doubt and total exhaustion I'd finally caught one.
As I took hold of the Bittern and started to extract it from the net I was shocked to see it was already ringed! The address on the ring began with a B. My mind was racing. Belarus! (Ken Smith, who has been leading Bittern research at the RSPB told me they're ringing some there, wherever there is). No, not Belarus Alan, it was British Museum. British Museum! A bird ringed in Britain. I couldn't believe it. I have firmly held the view (and still do, despite the present contrary evidence) that Bitterns wintering in the Lee valley are mainly of continental origin. But this one wasn't.
Ken Smith, Alan Harris and Gillian Gilbert radio-tracking the Bittern
I secured the bird and arranged to meet RSPB scientists Ken Smith and Gillian Gilbert. They duly arrived with the tag and information regarding the original ringing details. It had been ringed by Gillian as a female chick in Lincolnshire on 6 June 2001, one of a brood of five. Gillian hadn't been able to find the bird once it had fledged and had doubted its survival. With the tag fitted and operational the Bittern was released back into the Pochard Hide reedbed, and the tracking could begin.
The range of the tag is around a mile, but with longevity of perhaps a year.
So far (and it's early days), the Bittern has remained in the Pochard Hide reedbed almost all of the time, both roosting and feeding, with a short excursion to the Bittern Watchpoint, proving the very sedentary nature of some Bitterns once established in their winter quarters. I most look forward now to the spring. Will she go or stay, and if she goes, where to? Her departure will spark off a search in all the likely reedbeds in Britain, starting with Lincolnshire. Will she return next winter?
With all the effort going into reedbed creation in the Lee Valley it is heartening to know that a British-bred Bittern is already using the amenities. If Bitterns are to breed in the Lee Valley the pioneer birds are most likely to come from British stock. So, it's good news all round!
Alan Harris
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