Counting songs: estimating the UK’s Nightingale population

Nightingale - John Spaull
Large-scale population estimates of species are used for several reasons, including the assessment and protection of important sites. However, determining a national population requires extensive surveying and using methods that allow counts to be scaled up to the number of birds actually present and across a larger area.

This new BTO study looks at different methods used to estimate the population of Nightingales in the UK. Nightingales have declined by 61% in the last 25 years and therefore determining which sites contain the largest populations is vital. The study focused on 2733 2x2 km squares, 2356 where Nightingales were known to be, as well as randomly-chosen squares whose selection was stratified based on habitat suitability. By using different analytical methods, the final population was estimated to be between 5094 and 5938 territorial males, of which only 55-65% were counted during the surveys. It is therefore important to consider how to fully control for variability in detection and for birds outside of surveyed areas when estimating national populations.

The study also highlighted the importance of Lodge Hill SSSI for breeding Nightingales, which was designated for its nationally important population of the species, based on the results presented in this paper.

Related publications:

Hewson, C.M., Miller, M., Johnston, A., Conway, G.J., Saunders, R., Marchant, J.H. & Fuller, R.J. 2018
Estimating national population sizes: Methodological challenges and applications illustrated in the common nightingale, a declining songbird in the UK Journal of Applied Ecology.
Link to publication (DOI: 10.1111/1365-2664.13120).

Notes

This study would not have been possible without the 1281 surveyors who visited squares to survey Nightingales. The study was funded by Anglian Water with additional funds from donations by BTO members and supporters and the Nightingale Supporters Group. We are very grateful for the awards made to the survey by 14 charitable grant-making trusts (including the Chapman Charitable Trust, the William Haddon Charitable Trust, The Mercers' Charitable Foundation, The Michael Marks Charitable Trust and The Jack Patston Charitable Trust) and thank our Fundraising Team, especially Rachel Gostling and Sam Rider for organising the Nightingale Appeal.

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