How did two migratory birds trace us from the desert to the North Pole

This spring we were on an expedition with fellow migratory bird ecologists to Banc d’Arguin, a nature reserve made up of small islands and mudflats off the coast of Mauritania; Closed from one side of the sea, and from the other side the desert. It is one of the most waterfowl-rich nature reserves in the world and an important wintering area for many migratory birds, such as knotweed.

De Canuit

The red knot sandbird, commonly referred to as the short knot, belongs to the waders family and is about the same size as the blackbird. This is where the comparison with the blackbird ends. Nodes live almost all year round in mudflats, where they feed on shellfish. Except for the summer, when they change from their gray plumage to the bright red breeding plumage, they fly thousands of miles far north to breed. In the tundra, when the snow melts, there are a lot of insects. Knot chicks love it!

previously vs. right Now

In the 1980s, ecologists of migratory birds counted about 400,000 knots in the Darguin Bank (Bersma et al. 1990). Since then, the number of nodes in Mauritania has at least halved (Van Roomen et al. 2015; Oudman et al. 2020).

search

One possible reason for this dramatic decrease in the number of knots is located in Mauritania thousands of kilometers to the north. Due to global warming, snow on the tundra is now melting much earlier than in the 1980s (van Gils et al. 2016). In order to check whether the node can adapt the migration moment to this “new normal”, we equipped the nodes in Mauritania with a small satellite transmitter this spring and the local movements of the birds can be followed.

catch up first…

It’s clear: you first have to catch a bird before you can equip it with a transmitter. But this is not as clear as it seems. Node catching occurs in the middle of the night. Eva tells us about this: ‘It is preferable to have a new moon when it is very dark. With the help of long nets, somewhat similar to nets on a tennis court, the nodes are intercepted as they fly at night as the water rises to the high tide shelter.

…then broadcast

Small transmitters weigh only four grams. After all, the knot should be able to fly with it thousands of kilometers. After some feathers are cut, the transmitter is glued to the back of the knot. This may seem a little inconvenient, but as soon as the red knot checks its plumage after breeding, the transmitter drops again.

local eating habits

Knots store huge amounts of energy in the form of fat to block migration from the desert to the arctic. Within a few weeks, the node doubles its body weight. To verify the role of food during preparation for migration, we also imaged tagged nodes on the mudflats. In this video you can see how Tishot finds and eats an oyster. This way they can determine what and how much the bird eats for each individual node.

food and stool

But this study of diet is not complete unless you also look at the environment. Together with our colleagues, we took a soil sample in all places where marked knots were seen to find out what kind of prey was hiding at the bottom. And we collected stool from the knots, because the composition of the stool also tells us what the knot ate.

Arkeiss en Teichott

Knots Teichott and Arkeiss, both named after one of the many islands in Banc d’Arguin, were captured on the nights of April 7 and 10. While Arkeiss was already wearing beautiful red plumage, Teichott was still strikingly gray. In the four weeks after the transmitter, the birds got fatter, as we saw while filming Arkeiss and Teichott.

long-awaited departure

Knots leave Banc d’Arguin in the early days of May. At least, that’s the prediction based on observations about the decadent decade of Banc d’Arguin in the 1980s. Judging from the current situation of snowmelt in the tundra, we thought they might leave soon. So we’ve been in anticipation for several days when Arkis finally leaves the area on May 6. Tichot, the least reddish bird, even left a week later, on May 14.

Strong headwinds on the way

Arquis immediately flew on one long trip to a well-known resting place near La Rochelle in France. On the other hand, Tishote faced very headwinds off the coast of Western Sahara and settled for nine days on the mudflats near Faro (Portugal) before stopping again on the mudflats of La Rochelle, at the exact same place where Arkeiss spent three weeks. Before that he stopped it for the first time. Teichott then stopped for two days in Zeeland before spending a week along the estuary of the Ems. Meanwhile, the Arkeiss was along the Frisian coast for about three weeks and departed on May 29 for the coast of the Pechora Sea (Russia). After a layover of several days, Arkis arrived at the breeding grounds in Tajmir on June 7, exactly in line with the decade’s average arrival in the 1980s. Tishot arrived just over a week later on June 13, after a journey from the Wadden Sea with no further stops.

How are Arkeiss and Teichott doing right now? Follow their actions: https://www.globalflywaynetwork.org/flyway/

Would you like to read more background information about this project? View the NIOZ website: https://www.nioz.nl/en/research/projects/4440-1

quotes

Persma, T.; Klassen, M., Bruggemann, J.H., Plumert, A., Joy, A., Ntiamwa Baidu, Y, and Van Breederud, NE (1990). Seasonal timing of spring departure for waders from Bank Arguin, Mauritania. Ardea, 78, 123-134.

Oudman, T., Schekkerman, H., Kidee, A., Van Roomen, M., Camara, M., Smit, C., Ten Horn, J., Piersma, T., & El-Hacen, EHM (2020). ). Changes in the waterfowl community in the Parc National du Banc d’Arguin, Mauritania, 1980-2017. Bird Conservation International, 30(4), 618-633. https://doi.org/10.1017/S0959270919000431

Van Roomen, M., Nagy, S., Foppen, R., Dodman, T., Citegetse, G., & Ndiaye, A. (2015). Status of Coastal Waterfowl Populations in the 2014 East Atlantic Flyway. With particular concern for flyway populations benefiting from the Wadden Sea. 153. http://www.waddensea-secretariat.org/management/publications/status-of-coastal-waterbird-populations-in-the-east-atlantic-flyway-2014

Van Giles, JA, Lisovsky, S, Locke, T, Messner, W, Awarovska, A, de Vu, J, Rakhimberdiev, E, Solovyev, May, Bersma, T, and Klassen, M (2016). Body shrinkage due to higher arctic temperature reduces the fitness of the red knot in the tropical winter range. Science, 352 (6287), 819-821. https://doi.org/10.1126/science.aad6351