Once again seasonal ringing was carried out at Pensthorpe Natural Park by the Norfolk Ornithologists Association (NOA) as part of the British Trust for Ornithology’s long-term study on breeding success and survival rates of the UK's birds.
This was the twelfth consecutive year the study, known as the Constant Effort Site (CES) scheme, has taken place at Pensthorpe, which is one of only eight sites in Norfolk and one of 130 in the country.
During the breeding season ringing sessions are organized with as many variables being kept constant. This includes the periods between ringing sessions and the months of the year that they are to be carried out, all in an aim to provide an annual series of results that can be compared to previous years in a controlled and consistent way.
The data collected from Pensthorpe and the other CES’ throughout the country provide an
accurate measure of the increase and decrease in species numbers. These are then extrapolated to give a national picture. Recaptures of birds ringed in previous years allow survival rates to be calculated. The ratio of juvenile to adult birds caught on CES’ provides a second measure of breeding success that also takes into account the number of successful breeding attempts made per adult. Many species attempt to rear more than one brood per season and the survival of young birds immediately after fledging.
The study involves the erection of mist nets in pre-determined areas, for a specific time in pre-arranged date periods. Birds caught generally through the season at Pensthorpe are largely reed and wet scrub dwelling species, which is a reflection on the habitat. The typical species include reed and sedge warbler and, over the past couple of years, Cetti’s warbler. The latter, whilst a warbler species, is largely resident and prone to population fluctuations depending on winter weather conditions.
There were several surprises this year with above average numbers of greenfinch caught, which is encouraging following the species alarming decline caused by the parasite borne disease Tricomonosis.
The main highlight this year, from a numbers and ringing perspective, was most certainly the number of kingfishers caught during the season, with ten different birds caught and ringed. Nine of the ten birds caught were juveniles, which would imply good breeding success for the species locally.
Gary Elton, says: “Young kingfishers become independent of the parent birds within days of fledging and disperse widely. Adult birds can raise two broods a year, occasionally three, and brood sizes can be between four and eight; six-seven being largely the norm. That said, it’s highly likely these birds were probably, looking at the timings of the catches, from two or even three local broods though this is virtually impossible to prove with any certainty.”
This year Pensthorpe Natural Park’s avicultural Intern, Emma Buck, has been helping out with the ringing on her days off. Coming to Pensthorpe as this year’s Corncrake Nanny, Emma has been learning the ropes from Gary. She says: “Ringing at Pensthorpe has been really interesting as it can give us a snapshot of the health of the Wensum Valley and can help with conservation techniques. What started as a hobby is quickly evolving into a career for me and I have worked on ringing projects in Canada and Germany.”
This year’s success has been a great eye opener for Emma, spurring her on to
develop her career: “Highlights for me were the large volume of warblers who travel
amazing distances from Africa to breed in the UK. Another great moment was ringing a gorgeous Oystercatcher chick that I found as an egg, I watched it grow to the stage where it was big enough to ring and then saw it mature into a lovely juvenile when it had all of its flight feathers and disappeared off with its parents, who knows where it will be re-sighted?”
Commenting on a particular site in relation to the success of birds and species generally is always difficult as accurate conclusions are only really possible when the collated data from all the participating sites is taken into account. The information they gather is crucial in providing scientific data on population trends, the effects on climate change but also increasing the overall knowledge on bird species.
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