Subsequent Encounters

I was interested in item 9a on the agenda of the Ringing Committee meeting of April 25 - "BTO Expectations Regarding Generation and Submission of Ringing Data," particularly the requirement to submit retrap data, so I had a look at how we compare to what is expected by the BTO.

The BTO's analysis indicated that the average ratio of retraps to new birds for the vast majority of ringers falls within a similar range, averaging 22%. I guess this would very much depend on where and what species you are ringing. Their analysis focused on 10 common species of Blackbird, Wren, Dunnock, Robin, Long-tailed tit, Blue Tit, Great Tit, Coal Tit, Chaffinch and Goldfinch, for 2018, 2019, 2023 and 2024.

To get an idea of how we compare, I analysed SNRG data submissions for 2025 for these 10 species and the results were - 2866 new birds ringed and 1264 subsequent encounters, = ratio of 44.1%.

The following chart shows how these are broken down per species. 

So, if my methods and calculations are correct, SNRGs new to retrap ratio of 44.1% for these 10 "common garden" birds for 2025 was double the average!

This seems surprising and prompted a bit more investigation. The total of 4,130 birds were ringed across 19 sites, 8 of which are garden sites or sites where supplementary seed is provided. It's no surprise that feeding sites and gardens attract more birds, could our use of these sites account for our high ratio?

Another thought, and one we discuss often, is, could the loss of and deterioration of our "natural" sites, resulting in a focus on feeding sites, affect this ratio? So I did similar searches for several earlier years, and it appears we have been a high retrap ratio Group since the mid 1990s, averaging 37.0% over the targeted years. See chart below for more detail. Communications from the BTO mandating the submission of retrap data, in 2001 and 2005 accounts for some of the increase. 

Mick P