Diagnosing the recent population decline of black-tailed godwits in the United Kingdom

During the last 50 years, the breeding population of Continental Black-tailed Godwits Limosa limosa limosa in the United Kingdom has been relatively small (below 60 pairs) and largely concentrated in two locations in eastern England. There were severe declines at the Ouse Washes during the 1990s due to increased spring flooding. In the following years, there were increases at the nearby Nene Washes. However, since 2006, the population at the Nene Washes has been declining – from 48 pairs in 2006 to 37 pairs in 2014. With ~85% of the UK population relying on the Nene Washes, it is important to diagnose the cause of this decline. We do this by comparing adult, nest and chick survival estimates across two time periods when research projects were active: the ‘early’ period (1999–2003) when the population was rapidly increasing, and the ‘contemporary’ period (2015–2019), during the population decline. We found no clear difference in annual apparent adult survival rates between the two periods. However, both nest and chick survival were lower in the contemporary period (nest survival by 31–41% depending on lay date; chick survival by 59–72% depending on hatch date). We show that 61 of 63 Nene-hatched chicks known to have recruited did so back into the Nene Washes population. The recent decline is therefore not the result of changes in adult mortality or breeding dispersal, but insufficient breeding productivity leading to insufficient recruitment into the natal population. The decrease in nest survival in the contemporary period results from an increase in predation pressure, as only one nest was flooded and none were destroyed by agricultural activities. We discuss why predation pressure might have increased and whether this could also explain the observed change in chick survival. We go on to recommend research and management efforts that should be undertaken to stop further declines of this population in the short-and long-term.

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