16 November 2016

Ringing and nest recording; the dream 'info team'

Monitoring nests for the BTO Nest Record Scheme gives us a really good estimate of the number of fledglings produced from the average nest each year, but this is obviously only the first part of the story - for breeding success to have an impact on the future population size, these young birds have to make it through autumn and winter to the following spring. By fitting rings to chicks in the nest and recapturing them as free-flying individuals, volunteers are able to follow their progress over this period. Calculating post-fledging survival rates from these data is actually very challenging as many young will move from the site in which they were raised and settle to breed in areas where there is a lower chance of them being re-encountered. However, those that are observed subsequently provide vital information on dispersal and settlement, key processes by which birds are able to change their ranges over time in response to changing climate and habitat quality.   

Brood of Blue Tit chicks. Photo by Mainwaring

Another big advantage of ringing nestlings is that the exact age of re-encountered individuals is known. Most songbirds have replaced all their juvenile feathers by the end of their first breeding season and, from this point onwards, it is impossible to determine how old they are. As age can have significant impacts on behaviour and breeding success, precise information is very valuable. Another certainty established by ringing chicks is the breeding population from which they originated, allowing researchers to determine which areas are net producers of young birds, and which may be population sinks.

Dave Leech studying Reed Warbler nests. Photo taken by Lee Barber

The totals presented in the Ringing Report show that in 2015 alone, over 167,000 nestlings (termed 'pulli') were ringed across Britain and Ireland. In almost all cases, the chicks ringed in each brood would have belonged to the same species, but there are exceptions, as Ian Wrisdale explains:

On a relatively large site of former gravel pits, I run nest box monitoring scheme, a Constant Effort Site (CES) and conduct autumn/winter ringing between October and December. To avoid the possibility of winter flooding, the ringing activities move from the reedbed of the CES, to an area of scrub/young woodland on the opposite side of the site for the winter. Due to the site being a Site of Special Scientific Interest (SSSI), all of the ringing activities are in accordance with agreements with Natural England. The agreed purpose of the winter ringing is to catch winter thrushes; however, it usually entails catching many tits. Whilst the outcome of the nest boxes is usually recorded as, “Nest Empty”, the winter ringing serves to confirm this outcome, monitor the movement of the birds around the site and allows some comparison of breeding productivity with post-fledgling survival.

The reedbed and wet willow scrub of the CES. Photo by Ian Wrisdale

During the last two seasons I have had two mixed broods of tits sharing the same nest box. In both cases, the brood comprised several Great Tits and a single Blue Tit. It is usual to assume that a single Blue Tit would struggle to survive with such competition but, in both of these cases, there was no sign of a dead Blue Tit in the nest box and the outcome was recorded as, “Nest Empty”, assuming at least a partial success. The Blue Tit in question this year was ringed on the 28 May, at the same time as the seven Great Tits with which it shared the nest. But its survival was not confirmed until it was recaptured during the first of the winter ringing sessions, on the  02 October 2016. Whilst I was pleased and surprised to be able to confirm its survival, it was a small, possibly female, individual (wing 60mm, mass 9.8g), making its successful competition against the Great Tits seem all the more remarkable.

Winter ringing in woodland scrub. Photo by Ian Wrisdale

It is unlikely that I will be able to catch it during the breeding season, unless I can agree, with Natural England, to conduct some summer ringing sessions at the winter site or catch it on the nest, but it would be interesting to see if it goes on to breed successfully, or will it think it's a Great Tit.

Eds - If you are a ringer and regularly ring resident species at a site during the winter, it would be worth considering if you are able to find and record the nests of these species. Even getting in touch with your local nest recorder could be beneficial. As this post demonstrates, the quality of the data can be dramatically increased.

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