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Chough perching on rock
Image: Nigel Blake
On Islay as a whole, immature chough survival depends on tipulid abundance and environmental conditions in the months before they were born. However, the model that describes these patterns failed to predict the atypically low juvenile survival since 2007, indicating the importance of an additional unidentified factor. Moreover, within Islay, choughs fledged from regions with similar levels of breeding success consistently differed in their survival after independence, resulting in source and sink areas, and in some years at least, juveniles from different subpopulations feed and roost in different flocking areas. Thus at present it is unclear whether the effect on survival of natal region is caused by the condition of natal sites (e.g. parental condition/ home-range quality) or post independence flock site choice (e.g. prey abundance/ accessibility). It is important to maintain habitat in favourable condition near breeding sites, favoured flock feeding sites, and communal roost sites, but more research is needed to understand the recent atypically low post fledging survival, which could bring about population decline.
In Northern Ireland, the 12 pairs of choughs in 1950 have declined to just one pair in recent years. Limited demographic data suggest this was because immature survival was too low, with its effect mitigated by occasional immigration. Key-areas to target action are identified based on still suitable historic nest sites. The existing agri-environment chough option should provide suitable habitat in these places, but data on compliance suggests it is not always delivered. Ensuring immature choughs survive and recruit locally is a priority.
Following the arrival of at least three birds in 2001, choughs bred in Cornwall in 2002 for the first time since 1947. The single pioneer pair and subsequently their offspring have bred successfully each year with six probable and confirmed pairs in 2010, following a program of nest protection and targeted grazing agreements. Monitoring, that includes colour ringing, shows productivity and survival of Cornish choughs are as good or better than other populations, with numbers and range increasing year-on-year. Ongoing monitoring will record any decline in performance as degrees of inbreeding becomes common.
Dr Ian JohnstoneSenior Conservation ScientistE-mail: firstname.lastname@example.org
Scottish Chough Study Group, Glasgow University, Manx BirdLife, Isle of Man Government, Cross & Stratford Chough Colour-ring Project