About the Winter Ringing Project
Why do we need a Winter Ringing Project?
Approximately 25% of annual passerine ringing relates to birds captured during the winter. Winter ringing can play an important role in providing training and engagement opportunities, and the data collected can generate some information about inter-seasonal dispersal. Historically they have not, however, fed into the routine demographic outputs, monitoring survival and productivity, in the same manner that data produced via the ringing of passerines during the breeding season are able to do.
In 2020, data for the 44 species most-commonly encountered between the winters of 2007/08 to 2017/18 were analysed to ascertain whether these data could be used to calculate survival rates. A fundamental assumption of survival models is that birds that do not return to the capture site have died, and this is largely true in spring and summer, given that passerines are generally faithful to breeding sites. In winter, a greater degree of transience may be required to ensure that enough food can be found; indeed, much winter ringing is reliant on the provision of supplementary food, which could bias abundance estimates and measures of productivity based on age ratios. On the flip side, paucity of food can lead to aggregations of birds that are too thinly dispersed in the summer to enable sufficient samples to be captured, providing novel monitoring opportunities.
The initial results from this analysis were promising, with a number of species, including Blue Tit, Dunnock, Great Tit, Long-tailed Tit and Robin, demonstrating sufficient site fidelity to suggest that robust estimates could be produced. Coal Tit was also included in this group, and is of particular interest, given that capture rates during the breeding season are currently too low to enable equivalent analyses. A number of ‘non-CES’ species also showed potential if the data could be collected in a more structured manner, including key species such as Marsh Tit, Willow Tit, Bullfinch, Chaffinch and Goldfinch.
The 2020/21 Winter Ringing Project Pilot
Encouraged by these results, a pilot Winter Ringing Project was launched in the winter of 2020/21, running from December to February. The methodology was similar to CES, but the visit periods were extended to a fortnight to cope with more challenging weather conditions. The use of supplementary food was also permitted, given that catches were likely to be too low at most sites without this focus for birds. The use of sound lures was not permitted as this is likely to lead to biases in age, sex and species composition. Any type of site, from gardens to sewage works, could potentially be covered.
Take-up during the pilot winter was encouraging, with 111 sites submitting data, mostly gardens due to lockdown restrictions. Unfortunately, weather conditions and Covid-19 restrictions took their toll, with only a third of sites managing all six visits, although over half managed at least four.
Following the success of the pilot year, the project continued in 2021/22, with the sampling period extended from November to February, split into eight visit periods.
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