Earthworm abundance and availability does not influence the reproductive decisions of black‐tailed godwits in an agricultural grassland

Abstract

Maintaining the biodiversity of agricultural ecosystems has become a global imperative. Across Europe, species that occupy agricultural grasslands, such as black‐tailed godwits (Limosa limosa limosa), have undergone steep population declines. In this context, there is a significant need to both determine the root causes of these declines and identify actions that will promote biodiversity while supporting the livelihoods of farmers. Food availability, and specifically earthworm abundance (Lumbricidae), during the pre‐breeding period has often been suggested as a potential driver of godwit population declines. Previous studies have recommended increasing the application of nitrogen to agricultural grasslands to enhance earthworm populations and aid agricultural production. Here we test whether food availability during the pre‐breeding period affects when and where godwits breed. Using large‐scale surveys of food availability, a long‐term mark‐recapture study, focal observations of foraging female godwits, and tracking devices that monitored godwit movements, we found little evidence of a relationship between earthworm abundance and the timing of godwit reproductive efforts or the density of breeding godwits. Furthermore, we found that the soils of intensively managed agricultural grasslands may frequently be too dry for godwits to forage for those earthworms that are present. The increased application of nitrogen to agricultural grasslands will therefore likely have no positive effect on godwit populations. Instead, management efforts should focus on increasing the botanical diversity of agricultural grasslands, facilitating conditions that prevent hardening soils, and reducing the populations of generalist predators.

Does early spring arrival lead to early nesting in a migratory shorebird? Insights from remote tracking

“…For example, many migratory waders breed at high latitudes, where their capacity to breed earlier is likely to be constrained by arrival date and the time required between arrival and nesting (Gill et al 2014). In such species, breeding phenology can be influenced by the environmental conditions experienced during this period, such as temperature (Alves et al 2019, Meltofte et al 2021, snow cover (Meltofte et al 2007, Mortensen et al 2016, vegetation growth (Laidlaw et al 2020) and available food resources (Meltofte et al 2007, Mortensen et al 2016, Zhemchuzhnikov et al 2021, Lameris et al 2022; but see Verhoeven et al 2022), as well as the timing of arrival of the mate (Gunnarsson et al 2004).…”

“…2022; but see Verhoeven et al . 2022), as well as the timing of arrival of the mate (Gunnarsson et al . 2004).…”

A cross-continental analysis of the habitat requirements for stable Black-tailed Godwit (Limosa l. limosa) populations in Europe

“…These sites would additionally enable shorter foraging trips for adults, possibly increasing their own fitness as well as increasing their ability to protect their clutches and chicks against predators. This seems to be the case in some countries, where Godwit territories are mostly found in areas with higher soildwelling invertebrate abundance, such as Estonian coastal meadows , while in other countries, such as the Netherlands, Godwit breeding densities do not seem to correlate with the abundance of soil-dwelling invertebrates (Verhoeven et al 2022a). However, in the last case, the study analyses sites where the abundance is overall high compared to other countries where most sites are completely empty of soil-dwelling invertebrates (e.g.…”