A longitudinal study of the effects of trees, geese and avian predators on breeding wader meadow birds: the case of the Demmerik polder, the Netherlands

Wil L.M Tamis,Piet Heemskerk

doi:10.1007/s10344-020-01415-9

Abstract

In the Netherlands, breeding populations of wader meadow birds are in sharp decline. One possible cause is that breeding areas are becoming less open because of tall trees and other factors. The effects of tree lines are generally studied by means of transversal studies spanning a short period of time. We report on a longitudinal field study from 1993 to 2010 into the breeding densities of Eurasian Oystercatcher (Haematopus ostralegus), Northern Lapwing (Vanellus vanellus), Black-tailed Godwit (Limosa limosa) and Common Redshank (Tringa totanus) in the Demmerik polder, the Netherlands. One part of this polder, a nature reserve, has an older tree line, while two agricultural parts are divided by a newly developing tree line. As the tree line in the agricultural parts was developing, foraging families of Greylag Goose (Anser anser) showed a strong increase in only one of these parts during the breeding season. During the same period, the density of avian predators also increased in the whole polder. Analysis shows waders avoid trees in both situations: with an existing tree line (a static situation) and with a growing tree line (a dynamic situation). We investigated the possible role of geese and avian predators in explaining the decline in density of breeding wader meadow birds, by systematic comparison of several different models. In these models, the effect of the growing tree line has the greatest impact on breeding meadow birds. Models with geese describe the trends of breeding wader meadow birds better than those including avian predators, but since these two variables, geese and avian predators, are confounded, no definitive conclusion can yet be drawn. Potential explanations of and functional mechanisms behind the strong decline in breeding meadow bird populations in this area are discussed.

Highlights

Wader meadow bird species like Eurasian Oystercatcher (Haematopus ostralegus), Northern Lapwing (Vanellus vanellus), Black-tailed Godwit (Limosa limosa) and Common Redshank (Tringa totanus) are in the threatened category of the European Red List (Birdlife 2015).Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.The Netherlands is an important breeding area for these species, with over half the European population of the Blacktailed Godwit and about a quarter of that of the Eurasian Oystercatcher breeding here (BirdLife 2017)
We described the effects of the growing tree line along the abandoned railway, the increasing numbers of avian predators and the increasing numbers of geese, predominantly present in the northern quarter of the agricultural area
There has been a marked decline in wader meadow birds in all three quarters of our study area, less in Res-S, intermediate in Agri-S and strong in Agri-N; see Appendix 2, Table 8

Summary

Introduction

Wader meadow bird species like Eurasian Oystercatcher (Haematopus ostralegus), Northern Lapwing (Vanellus vanellus), Black-tailed Godwit (Limosa limosa) and Common Redshank (Tringa totanus) are in the threatened category of the European Red List (Birdlife 2015). The Netherlands is an important breeding area for these species, with over half the European population of the Blacktailed Godwit and about a quarter of that of the Eurasian Oystercatcher breeding here (BirdLife 2017). In the Netherlands, as elsewhere, these meadow bird species are in sharp decline (Teunissen and Soldaat 2005, Koffijberg et al 2010; Teunissen and Van Paassen 2013; Eugster 2013). The Dutch breeding population of the Black-tailed Godwit (currently estimated at 33,000 pairs) has declined by two-thirds since the 1970s (Kentie et al 2016). Several factors are contributing to the sharp decline in meadow bird populations.

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