Wader population trends and productivity 1987–2022 in Mid Deeside, North-East Scotland, and the factors driving them

D. JENKINS, T.H. SPARKS & D.M.B. PARISH

Long-term population trends are described for Lapwing, Oystercatcher and Curlew on Deeside, with accompanying breeding productivity figures for the first two species. Population trends are more positive for these species on Deeside than in Scotland at large or the UK, though there is evidence of a decline for Curlew. Breeding densities were much higher on the hill-farm Birse Glen sites than on the low-lying Flood Plain sites. We suggest that this is the result of differences in agricultural practices in the two areas, rendering Flood Plain less suitable for breeding waders, and to reduced productivity at the Flood Plain sites due to high rates of egg and/or chick predation. Wader populations on the Flood Plain sites are not sustainable and must be maintained by immigration from source populations. Source populations of waders in the UK and across much of Europe are highly unlikely in the absence of sympathetic habitat management coupled with legal predator control.

Introduction

Breeding waders have declined over recent decades in the UK (Woodward et al. 2020). For Lapwing Vanellus vanellus, Oystercatcher Haematopus ostralegus and Curlew Numenius arquata, survival rates have remained high or are increasing and it is accepted that the main factor limiting population growth is a low reproductive rate (Roodbergen et al. 2012). That said, the period of steepest population decline for the Lapwing (1980s) was also associated with decreased adult survival related to a series of harsh winters, but survival rates have since recovered (Robinson et al. 2014). Low reproductive success has been associated with changes in agricultural land use (e.g. Taylor & Murray 2004, Bell & Calladine 2017, Franks et al. 2017) and increased egg and chick predation (e.g. Valkama & Currie 1999, Fletcher et al. 2010, Roodbergen et al. 2012, Ludwig et al 2019). These two factors are often intimately linked, with habitat alterations sometimes increasing predation rates (e.g. Baines 1990, Chamberlain & Crick 2003).

Of the three species considered here, Lapwing and Curlew currently have UK red list status and Oystercatcher amber (Stanbury et al. 2021), with UK population declines of 43%, 48% and 24% respectively between 1995 and 2018 (Woodward et al. 2020). Lapwings have greatly decreased in Mid Deeside where they were formerly widely distributed (Buckland et al. 1990). Now, they are usually confined to the few traditional lowland farms and wetlands with or near short grass, and to grassy areas on hill farms.