Effects of habitat quality and fragmentation on Woodlarks (Lullula arborea) and their invertebrate prey in intensively managed vineyards

Abstract

Vineyards in Switzerland are among the most intensively managed perennial crop systems. The vast majority of all parcels are treated with herbicides and do not have any ground vegetation cover, whereas only a small proportion of vineyards is managed extensively, allowing ground vegetation to grow. These contrasting management types lead to a fragmented and almost binary system of few vegetated parcels embedded within herbicide-treated ones. The Woodlark (Lullula arborea) is an endangered insectivorous bird species, which has its Swiss stronghold in this intensively managed agroecosystem. In a first study we assessed Woodlarks' habitat preferences during territory settlement and linked the birds' occurrences to their invertebrate prey. Woodlarks showed a clear preference for vegetated vineyard parcels with higher abundances and richness of invertebrate prey but also increased plant richness. Given the importance of invertebrates for Woodlarks, we investigated the scale-explicit effects of fragmentation (number of vegetated patches) and habitat amount (area of vegetated patches) on invertebrate abundance, in a second study. Our findings demonstrate that (fine-scaled) habitat amount and (broad-scaled) fragmentation directly impede the movement of invertebrate prey, as in areas with less vegetated area, scattered into many single patches, abundance was strongly decreased. Further, a multi-scale habitat selection analysis based on Woodlark telemetry data (36 birds), revealed that, inter alia, habitat amount and fragmentation showed an interdependent effect on Woodlarks' habitat use. This is, in areas with low habitat amounts (<20%), fragmentation negatively affected Woodlark presence, while in areas with higher amounts of vegetated surfaces, fragmentation even positively influenced occurrence probability (Fig. 1). This indicates that, given enough available habitat, the birds prefer a certain habitat heterogeneity on a home range scale. Further, we found positive effects of steppe habitats and forests being present within their home ranges. Our results thus suggest that the installation of a network of well-connected vegetated vineyards with increased plant richness, but which do not cover 100% of the home range surface, may promote the abundance of invertebrate prey and ultimately improve the habitat matrix for insectivorous species such as the Woodlark. Also, this matrix should include semi-natural habitats such as steppes and forests, which need to be protected from further conversion and fragmentation.

Fig. 1. Interdependent effects of habitat amount (PLAND) and fragmentation (PD) on Woodlarks habitat selection. If habitat amount is low (< 20%, light green curve), Woodlarks prefer aggregated patches of vegetated vineyards. On the other hand, if habitat amount is high (> 30%), the birds select for areas where vegetated vineyards are distributed heterogeneously (positive effect of fragmentation).