Bird migration Billions of birds are on their way south

Every autumn, an estimated 50 billion migratory birds fly to their wintering grounds worldwide. According to estimates, five billion birds make the journey from Europe to Africa alone each year.

The birds do not migrate south because it gets cold, but because they can no longer find food, as Livio Rey from the Swiss Ornithological Institute in Sempach explained to the Keystone-SDA news agency. When it gets cold, there are hardly any insects left in this country. Birds that feed on insects therefore move away in winter. Birds that can change their diet or eat grains anyway stay here.

Cuckoos are the first birds to leave Switzerland. They leave for their wintering grounds south of the Sahara as early as mid-July. Other long-distance migrants such as swifts, black kites and orioles follow shortly afterwards. "Basically, the earlier the birds leave, the sooner they spend the winter in Africa," said Rey.

Those bird species that spend the winter in southern France or Spain leave later. The last birds to head south usually leave Switzerland around October.

Inner clock shows time of departure

While the short-distance migrants react flexibly to current weather conditions, it is strongly anchored in the genes of long-distance migrants when they have to take off. "Hormones are activated at a certain length of day and night, which is when the birds' migratory restlessness begins," explained Rey.

This strong internal clock is increasingly becoming a problem for the birds. Due to global warming, spring begins earlier in Europe every year. However, the long-distance migrants only change their schedule slightly. As a result, they miss out on the best conditions for their breeding season and, according to Rey, sometimes have fewer young or are less able to feed them.

Of the short-distance migrants, on the other hand, certain birds that used to fly south in winter are increasingly staying in Switzerland. These include white storks and red kites.

For some birds, Switzerland is the south

The annual departure of migratory birds from Switzerland does not mean that bird migration is over, emphasized Rey. This is because Switzerland's lakes are an attractive wintering ground for many water birds. Around half a million waterfowl spend the winter here, as is known from corresponding counts.

However, the number of waterfowl spending the winter in Switzerland is decreasing, as climate change means that the lakes in the breeding grounds of many birds no longer freeze over in winter. Following the trend of previous years, the numbers of wintering waterfowl were also very low this winter. In January 2024, only around 360,000 individuals were counted in Switzerland, including border waters.

SDA