Breeding populations of a declining farmland bird are dependent on a burrowing, herbivorous ecosystem engineer

Abstract

In recent decades, numerous farmland birds have experienced considerable population declines. The loss of nutrient-poor habitats with short vegetation due to land-use intensification, abandonment or nitrogen deposition helps account for this decrease. Soil-disturbing ecosystem engineers can naturally create short and sparsely vegetated swards with beneficial effects for biodiversity. The aim of this study is to examine the influence of the European rabbit (Oryctolagus cuniculus) as an ecosystem engineer on breeding populations of the severely declining northern wheatear (Oenanthe oenanthe) on the East Frisian Islands (Lower Saxony, northern Germany). Rabbits were found to have had a considerable influence on the structure of the dune grassland, the main breeding habitat of the wheatear: high rabbit abundance resulted in greater burrow density and more bare ground. Wheatears were also more abundant on islands with larger rabbit populations. At the plot level, wheatear abundance increased with burrow density and the cover of potential foraging habitats (short vegetation). In addition, the likelihood of nest-building increased with burrow density and decreased with vegetation height. We thoroughly investigated the dependence of the northern wheatear on large populations of the ecosystem engineer European rabbit. Through their digging and grazing activities, rabbits create two key resources for breeding wheatears: (i) sufficient burrows as potential nesting sites and (ii) the availability of short vegetation as foraging habitats.