27 April 2015

RAS double century

The Retrapping Adults for Survival (RAS) scheme was established in 1998 and uses bird ringing to monitor survival rates of a range of bird species. Coverage is particularly aimed at species which, due to their behaviour or the habitats they occupy, are not often caught by standard mist netting activities in woodland, wetland or scrub, such as Swallows, Dippers, Pied Flycatchers and many seabirds and raptors.

With the RAS season already underway for many species, registrations for new projects have been arriving thick and fast here at BTO HQ. At the time of writing, a fantastic 19 new projects, covering 16 species, have registered to start in 2015. A milestone was reached a few days ago with the registration of a new Tree Sparrow project in Cleveland which became the 200th active RAS project.

Tree Sparrows are a species of high conservation concern due to a spectacular crash in numbers of breeding birds between the late 1970s and early 1990s. Whilst BBS data suggest a significant increase in numbers since 1994, maps from the latest Bird Atlas show breeding Tree Sparrows as being absent from much of the south and west of the country and also declining in abundance south of the Midlands.

Maps reproduced from Bird Atlas 2007–11, which is a joint project between, BTO, BirdWatch Ireland and the Scottish Ornithologists’ Club. Map reproduced with permission from the British Trust for Ornithology.

Tree Sparrow is one of the RAS target species identified in the demographic targeting strategy. Currently, only one project, a study in Durham, has been running for long enough to contribute to the RAS survival trend, and the results suggest that, on average, about half of all adult Tree Sparrows breeding in 2015 will still be alive in 2016. But is this the case at other sites across Britain & Ireland? With two new RAS projects starting in 2015, the total number of active studies will increase to six, giving a much better idea of the national picture.

One project currently contributes to the national survival rate trend for Tree Sparrow (solid line), which shows that around half of the birds alive in one year currently survive to the next; the quality of the trend is considered to be 'uncertain' as the errors (dotted lines around the solid line) are relatively large – addition of more projects will help to reduce the size of these errors. 

There have been recent increases in the number of projects for Mute Swan (now three active projects), Starling (now 10 active and five historical projects), Swift (now three active and two historical projects) and House Sparrow (now 21 active and 12 historical projects) which is fantastic. It would also be beneficial to have a few more projects on species such as Tawny Owl, Barn Owl and House Martin to allow us to produce more accurate trends for these species.

It is rare for all active projects to run in a given year and there are always a few projects that have to end for one reason or another. That said, with more projects still registering for 2015, it would represent an incredible effort if the number that submit data this year hits the 200 mark for the first time.

A massive thank you to all current, past and soon-to-be RAS ringers for their tremendous efforts. Keep an eye on the website for the 2014 results which will be published soon.

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