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Migratory bird struggles with climate – pied flycatchers lay their eggs too late

May 15, 2001

They try very hard, but pied flycatchers are not able to adapt sufficiently to the climate change in Western Europe. Dutch ecologists state this in Nature's issue of May 17 2001. Spring in Western Europe warmed up during the past 20 years and became increasingly ‘early’. However, the migratory flycatchers are still arriving at the same date after their stay at the wintering grounds in tropical Africa. Christiaan Both of Groningen University and Marcel Visser of the Netherlands Institute of Ecology NIOO discovered that the birds have trouble to predict the start of the European spring while in Africa. Therefore, the females have to pick their partners and lay their eggs in a great hurry.


“The pied flycatcher is laying its eggs earlier than 20 years ago,” says NIOO scientist Marcel Visser. “But this is not enough: they have to advance their egg laying still more to keep up with the early springs. Why have they not done that yet? Because they do not return earlier from their wintering grounds in Africa. This CONSTRAINS their possibilities of adaptation to the climate change.” A typical problem for a long-distance migratory bird.
Pied flycatchers (Ficedula hypoleuca) breed in a large part of Europe: France, Great Britain, Scandinavia, Germany, and all the way east to the Ural.

Nowadays, spring in the temperate areas of the world is some degrees warmer then it used to be, causing many trees to bud burst earlier. Insects feeding on young tree leaves appear earlier as well. Flycatchers can only raise their young in a period with lots of insects available. They have to start laying eggs earlier to profit from the peak abundance of insects in early spring. But data from the Birding group Arnhem show that the black-and-white birds do not arrive any earlier in the Netherlands. They have to hurry extensively to try and profit from the insect peak as much as possible. A substantial number of the birds is too late for the OPTIMAL MEAL.

The flycatchers start breeding about 10 days earlier than in 1980. This causes the females to reduce their ‘relaxing’ period after their long travel from two or three weeks to only one. The migration costs a lot of energy. The species spends winter south of the SAHARA and have to ‘refill’ with energy afterwards. Still, the adaptation of the females has not been enough. The increased selection for earlier breeding provides us with the proof. Earlier breeders are ever more successful.
For the males it is of the utmost importance to arrive early. From mid-April onwards they start to enter the European breeding areas. A week later the females follow. “The males have to fight for the good-quality territories. Females choose their partner on the basis of their territory,” explains Christiaan Both. As male pied flycatcher you only are attractive when possessing an attractive territory.
The ‘girls’ are in hurry at arrival. Are they less choosy in their QUEST FOR A PARTNER because of that? Both: “That is what I like to know! You have to bear in mind that the choice of the right husband is very important. For example if a female picks a man with already another wife, she has to carry out all the work on her one.”

The thing causing this migratory bird trouble is the unchanged conditions at the wintering grounds. When the daylength becomes long enough, the birds start travelling. Arrived in the far away breeding areas spring appears to be early all of the sudden. Visser: “Until recently it all FITTED PERFECTLY TOGETHER. Now the climate is changing, the rules are no longer valid. We see something similar in great tits (Parus major).” The biologists study the flycatchers in the Dutch National Park ‘De Hoge Veluwe’. The Netherlands Institute of Ecology NIOO follows this population of pied flycatchers already from 1959, when the first couples started breeding in the nest-boxes. On this very moment about 100 pairs are busy breeding.

The scientists stress the point that long-term studies of individually recognisable, marked animals are important. Visser: “Such data is very valuable. This really shows the results of climate change.” NIOO has planned a follow-up for the next three years. Why do the flycatchers not start migrating earlier? “Are they not able to or do they not want it? That is a large difference.”


Netherlands Institute of Ecology (NIOO-KNAW)