I am doing a PhD project about earthworms in dairy farmland. Although it may sound as it has little to do with waders, it is actually about the foraging ecology of waders using dairy farmland to feed on earthworms (e.g. Black-tailed Godwits, Lapwings, Ruffs, Golden Plovers etc.). I am mainly focusing on how management of grasslands used for dairy production influences different earthworm species.

Ruffs and Golden Plovers feeding on earthworms. Photo: Jeroen Onrust

There are two main groups of earthworms, species that surface and species that don’t surface. Especially the surfacing species are important as by coming to the surface they are then also available for visual hunting birds such as Lapwings. A probing Black-tailed Godwit could feed on both groups. To measure earthworm availability for a Lapwing or other visual hunting earthworm predators, I developed a cart that can be pushed slowly with the legs along a transect and then all the earthworms could be counted form close distance without creating too much disturbance (see picture). It is night work as earthworms only surface then.

Jeroen counting earthworms by pushing himself slowly along a transect using a self-developed cart. Photo: Lars Soerink

Nevertheless, I did also true wader-work during my PhD. We studied nocturnal movements of Golden Plovers wintering in dairy farmland to investigate whether they use earthworm-rich patches for foraging. For two years, we applied TOA transmitters on 50 birds and measured number of surfacing earthworms in the patches an individual used at night and compared it with nearby unused patches. Furthermore, by performing indoor feeding experiments, we revealed how Ruff catch earthworms. Also during my study biology at the University of Groningen I worked with waders (Oystercatchers and Redshanks at the saltmarsh and Red Knots in Banc d’Arguin).

I am based at the University of Groningen (NL), but my project is funded by the University Campus Fryslân in Leeuwarden. Therefore, I am doing most of my fieldwork in Friesland. I’m supervised by Theunis Piersma and Han Olff.

Profile photo: Lars Soerink