Every year, a team conducts a census and bands migratory birds at the Marcenay pond in Côte-d’Or. This delicate yet crucial task is essential for studying the stopover strategies of birds, which have been disrupted this year by drought.
Marcenay (Côte-d’Or), coverage
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The Marcenay pond, located in the northern part of Côte-d’Or, glistens under the summer sun. It’s barely 10 AM, and the temperature is already nearing 30°C. At the base of the pond’s birdwatching observatory, the relentless heatwave gripping France is palpable. Simon-Pierre Babski, the scientific director of the Côte-d’Or Bird Protection League (LPO), hands us waterproof overalls with built-in boots.
We make our way through a narrow, muddy path—usually submerged—amidst reeds and purple loosestrife flowers to reach the stagnant water. Here, we board a canoe with the goal of carrying out a banding operation. This annual task, performed each August by the Center for Research on Bird Population Biology (CRBPO) of the National Museum of Natural History (MNHN), involves placing a band on a bird’s leg to identify and monitor them, aiding in documenting shifts in their migratory stopover strategies.
“The pond is a magnet for hundreds of marsh-dwelling migratory birds: they rest here post-breeding and before winter migration to replenish their fat reserves,” Simon-Pierre Babski explains. The open water, reed bed, and moist woodlands of this 115-hectare sensitive natural area draw species like the Savi’s warbler, reed warbler, yellow wagtail, and bluethroat each summer. “But normally, there’s 40 to 50 cm more water here!” he adds.
At the end of our canoe journey, we meet Joseph Abel, an ornithologist and ringer, and director of LPO Burgundy-Franche-Comté, along with Margot Perrot, a volunteer assistant ringer. They are retrieving birds caught in the fine mesh of eighteen vertical nets set up in the reed-covered area.
Surrounded by dense vegetation, Margot Perrot notices several changes compared to her first expedition in the reed bed a week earlier. “We used to get stuck in mud in some places at the start of the banding camp. Now, it’s dry enough to walk on normally; it’s astonishing!” she exclaims, pointing to clumps of overturned soil.
The recent weeks of heat and drought have not only affected Marcenay pond but have also brought concerning low water levels across Côte-d’Or. On August 3, the prefecture declared a state of crisis in 11 of the 14 hydrological zones of the department. Many water bodies in the Burgundy-Franche-Comté region are drying up.
Looking up, the 25-year-old apprentice ringer spots a tiny brown and beige songbird tangled in the net. “This is a small Savi’s warbler, typical of the reed beds,” she quietly explains while carefully freeing the bird to minimize stress. “We need to act quickly, but gently!”
Margot Perrot places the bird in one of the fabric bags she wears around her neck, to take it back to the study site. “It’s very, very hot,” she remarks. “That’s why we regularly check the nets, to minimize the time the birds spend trapped in the full sun.”
On the worktable are spread a precision scale, an ornithological caliper, and tracking sheets. Simon-Pierre Babski takes a garden warbler, a small gray bird about twelve centimeters long, from one of the bags, while Margot Perrot prepares to diligently record the data. “This individual was born this spring, so I can’t determine its sex,” Simon-Pierre, a certified ringer by the MNHN since 2016, informs her. He blows on the bird’s belly to assess its fat reserves, measures its wing, tarsus, observes its molting… All relevant data is recorded. The warbler is then placed headfirst into a small tube on the scale: “19.9 grams.”
Before releasing it, a unique numbered metal band will be placed on the bird. The purpose? To better understand the marsh birds that stop over at Marcenay, “and study the variations in their migratory stopover strategies over the years,” details Simon-Pierre Babski. “Especially in relation to external factors such as climate change and the management of the pond to preserve biodiversity.”
Elsewhere, a dragonfly flits between the reeds. However, this summer, Joseph Abel notices hardly any damselflies (also known as zygoptera). “There are a few dragonflies around, but they’re few and far between. Normally, we see mats of red-eyed naiads on the vegetation. Now, there are none at all,” he remarks. However, it’s hard to confirm whether this absence is linked to the successive heatwave and drought episodes. “Since it’s been very hot, maybe they emerged earlier, or there was no emergence… It’s just a feeling,” Joseph Abel admits.
For Aurélien Gréaume, a mission officer at the Burgundy Natural Spaces Conservatory — which co-manages the site with the Côte-d’Or Federation for Fishing and Aquatic Environment Protection —, repeated droughts create stress on the different habitats of the pond. “We have somewhat earlier flora, which dries up quicker, or even burns a bit while standing. And this can impact the fauna living there, more or less strongly depending on the species,” he laments.
Around a clump of reeds, high-pitched whistles are heard. Could it be Savi’s warblers? “That’s the playback,” Simon-Pierre Babski jokes. “Our sound lure system that plays songs of migratory passerines intended to attract birds into the nets.”
A few more reed warblers, a bluethroat, a willow warbler, and a marsh warbler later, and the ringers, exhausted by the heat, fold up the large nets of the reed bed. In total, 128 birds were checked or banded that morning. Since 2009, nearly 69,000 birds have been banded or checked at Marcenay.
Simon-Pierre Babski’s task now is to enter the codes and figures collected at Marcenay onto the MNHN site, which will then be forwarded to Euring, the European bank that compiles data from migratory birds handled by all ringers in Europe. By 2025, more than 90,000 migratory birds had been monitored under the Séjour program by nearly 400 French ringers, often volunteers.
These data are a “gold mine” for scientists, asserts Maud Mennerat, a doctoral student in ecology at the MNHN Center for Ecology and Conservation Sciences. By analyzing eleven years of Séjour program data, she discovered that European migratory passerines generally delayed their migratory passage date in autumn, with variations depending on the species. “It’s likely related to environmental factors,” the doctoral student explains. “But it’s not easy to say for now, as everything happens over a long period.”
For Maud Mennerat, periods of drought and local water level declines are not enough to explain this change. “As long as the birds have a relatively preserved habitat and food resources at their stopover sites, it’s difficult to draw conclusions,” she continues. “We don’t yet know how to analyze a prolonged presence at a stopover site or an increase in the number of individuals: are the birds stopping because the place is welcoming? Or because the surrounding sites are worse, and they can’t go elsewhere?”
Therefore, the effects of weather and climatic conditions on variations in migratory strategies remain a subject for further study. “These are investigations to be carried out, as the episodes of heatwaves and drought we are experiencing are historic,” affirms Pierre-Yves Henry, director of the CRBPO and professor at the National Museum of Natural History. This work could begin as early as next year, once new data from all migratory stopover sites in France are available.
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Hi, I’m Ashley from the Decatur Metro team. I share essential information for a sustainable and responsible lifestyle.
