ten Horn, J. | bioRxiv Science

bioRxiv2022

Disentangling the diet composition of chicks of Arctic shorebirds provides a new perspective on trophic mismatches

With rapid climatic changes over the past decades, organisms living in seasonal environments are suggested to increasingly face trophic mismatches: the disruption of synchrony between different trophic levels due to a different phenological response to increasing temperatures. Strong effects of mismatches are especially expected in the Arctic region, where climatic changes are most rapid. Nevertheless, relatively few studies have found strong evidence for trophic mismatches between the breeding period of Arctic-breeding shorebirds and the arthropod prey on which they rely. Here we argue that this is potentially caused by a generalisation of trophic interactions. While many studies have measured the mismatch relative to the peak in abundance of all available arthropod species, we use metabarcoding of prey items in faeces to show that chicks of four different shorebird species (red knot, curlew sandpiper, little stint, and red phalarope) strongly differ in their arthropod diet. Three out of the four species feed on arthropods peaking in availability five-ten days before the overall arthropod peak which had implications for the calculations of trophic mismatches. We conclude that ignoring diet selectivity hampers our understanding of phenological mismatches.

ecology↗

bioRxiv2021

WATLAS: high resolution and real-time tracking of many small birds in the Dutch Wadden Sea

BackgroundTracking animal movement is important for understanding how animals interact with their (changing) environment, and crucial for predicting and explaining how animals are affected by anthropogenic effects. The Wadden Sea is a UNESCO World Heritage Site and a region of global importance for millions of small shorebirds. Due to climate change and anthropogenic activity, understanding and predicting movement and space-use in areas like the Wadden Sea is increasingly important. Monitoring and predicting animal movement, however, requires high-resolution tracking of many individuals. While high-resolution tracking has been made possible through GPS, trade-offs between tag weight and battery life limit its use to larger species. MethodsHere, we introduce WATLAS (the Wadden Sea deployment of the ATLAS tracking system) capable of monitoring the movements of hundreds of (small) birds simultaneously in the Dutch Wadden Sea. WATLAS employs an array of receiver stations that can detect and localise small, low-cost tags at fine spatial (meters) and temporal resolution (seconds). From 2017-2021, we tracked red knots, sanderlings, bar-tailed godwits, and common terns. We use parts of these data to give four examples on its performance and how WATLAS can be used to study numerous aspects of animal behaviour, such as, space-use (both intra- and inter-specific), among-individual variation, and social networks. ResultsAfter describing the WATLAS system, we first illustrate space-use of red knots across the study area and how the tidal environment affects their movement. Secondly, we show large among-individual differences in distances travelled per day, and thirdly illustrate how high-throughput WATLAS data allows calculating a proximity-based social network. Finally, we demonstrate that using WATLAS to monitor multiple species can reveal differential space use. For example, despite sanderlings and red knots roosting together, they foraged in different areas of the mudflats. ConclusionsThe high-resolution tracking data collected by WATLAS offers many possibilities for research into the drivers of bird movement in the Wadden Sea. WATLAS could provide a tool for impact assessment, and thus aid nature conservation and management of the globally important Wadden Sea ecosystem.

ecology↗