The Wadden Sea is a highly valuable, 500 km stretch of dynamic coastline in western Europe between the Netherlands and Denmark. This area is the largest connected intertidal flat system in the world. During low tide, the densely populated benthos provide a food source for shorebirds who stopover, roost, or nest in the region. The Wadden Sea is located along the East Atlantic Flyway and is used by millions of birds annually. Some of these birds travel extreme distances between their wintering grounds in Africa and their breeding grounds in Siberia, with just one stopover in the Wadden Sea. Conditions (like resource availability) during staging also impact the birds in other parts of their lives. To understand the potential impacts of changes to the staging area (due to climate change or disturbance), we must first have a strong understanding of the foraging ecology of individual species. Here I outline some of the tools and methods we are using to study the foraging ecology of the Bar-tailed Godwit.  

The Wadden Sea Advanced Tracking and Localisation of Animals in real life Systems (WATLAS) is a tracking system which uses an array of receivers and small tags to provide tracking data with high spatial and temporal resolution. The tags are small, and are glued to the back of birds that have been caught with mist nets. This type of tag securement to the bird ensures that the tags are temporary, and will fall away from the bird during their first molt after being tagged. However, while they are here in the Wadden Sea, amongst the receivers, we can understand what areas they are using, and how frequently or how long they use these areas.

The Synoptic Intertidal Benthic Survey (SIBES) is a long-term sampling program that has been conducted across the Dutch Wadden Sea since 2008. Every year ~5,000 samples are taken of the intertidal flats. The data from these samples provides us with information about sediment characteristics, benthic species abundance, assemblage, and individual condition across the entire study area. For topics like foraging ecology of shorebirds, this data can be used to create a "food map" which can be compared to the tracking data mentioned above to understand if birds are selecting areas with certain prey, or certain densities of prey, through resource selection modelling.

We also use a series of observations in the field to understand the foraging ecology of Bar-tailed godwits during their stopover in the Dutch Wadden Sea. We spent a lot of time observing the birds and collecting data; for the value of the data certainly, but also because we believe that familiarity with your study system can increase the quality of your science!

After observing groups of foraging Bar-tailed Godwits in the field we collected samples of the prey available in that location, and stool samples. The prey samples were collected with the same methodology as the SIBES samples mentioned above. These samples were collected so we could understand how much energy is available to the birds in the prey they are consuming, specifically win the areas we found them foraging. To determine the energy content per individual prey item, we identified prey to the species level in the lab, then counted them and placed them in crucibles so they could be incinerated. Ash-free dry mass (AFDM) is determined by drying a sample, weighing it, incinerating it, and weighing it again. Anything that can burn is the "available" energy. This method removes the issue of varying amounts of water or sand inside of the individual prey.

To analyse the droppings of foraging birds, we carefully sort through the samples under a microscope and look for hard parts of prey. This includes exoskeletons of crustaceans, hinges of bivalves, chaetae of polychaete worms, and jaws of polychaete worms.