French flamingos froze to death without freezing

One of the best spots to find flamingos is in southern France. In the Camargue, some 10,000 to 15,000 flamingo couples gather each year, feasting on tiny invertebrates in the region’s waters. Some of the birds migrate to North Africa for the winter, while others stick around in France. But staying behind can be deadly. In 1985 and 2012, severe cold spells killed thousands of birds.

Anne-Sophie Deville of the Centre de Recherche de la Tour du Valat in Arles, France, and colleagues wanted to figure out why the flamingos died. Cold can kill in a number of ways, and freezing is only one of them. Deville and colleagues didn’t have any carcasses from the 1985 event, but 30 flamingos that had died during the 2012 event were dissected.

The birds were “extremely lean,” the researchers report October 15 in the Journal of Experimental Biology. Their energy stores were comparable to those of woodcocks that had died from starvation during a bad cold spell. They were also lower than those of mallards in the often-fatal last stage of fasting, when the body consumes the protein in muscles in a last-ditch effort to prevent starvation.

Camargue was really cold during the January 1985 and February 2012 events. The average winter temperatures for the region are around 7 or 8° Celsius, but conditions during the cold snaps were much colder, reaching as low as -10.6° C in 1985 and -6.6° C in 2012. That froze the waterways where the flamingos got their food. But the loss of food wasn’t the only problem — it was the timing.

Deville and colleagues calculated the flamingos’ energy needs throughout the year and found that they peak in January. In normal winters, the birds manage to get enough food to survive. But in 1985 and 2012, when their food was cut off, many of the flamingos starved, unable to survive on their fat and protein stores long enough for the water to thaw and give them a good meal.

But if starving to death is a real danger for the birds, why don’t they all migrate south for the winter? Well, migration can be dangerous. And for young birds, staying close to home or migrating only a short distance is actually the less dangerous option. First- and second-year flamingos that attempt the long-distance wintering usually die in greater numbers, researchers reported in 2012 in the Journal of Animal Ecology. It’s only once the birds are older that the long-distance migration strategy pays off and they survive better than brethren that stayed in France, whether there’s a cold snap or not.