Estimating national population sizes: Methodological challenges and applications illustrated in the common nightingale, a declining songbird in the UK

Nightingale - John Spaull

Author(s): Hewson, C.M., Miller, M., Johnston, A., Conway, G.J., Saunders, R., Marchant, J.H. & Fuller, R.J.

Published: February 2018

Journal: Journal of Applied Ecology Volume: 55 ( part 4 )

Digital Identifier No. (DOI): 10.1111/1365-2664.13120

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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.

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