The cold lasted a very long time this year, which meant that nature only got going very late. In recent years, spring had actually been getting earlier and earlier. Christiaan Both, professor of animal ecology at the University of Groningen, about the consequences for nature: ‘Spring is now starting at the same time as thirty years ago. This will set the early adaptations of birds like the pied flycatcher back years.’
‘In the last 25 years, the average temperature in the second half of April and the first half of May has increased by no less than 3.5 degrees. That has had significant effects on nature. When the trees come into leaf, there’s a peak in the number of caterpillars. Birds like the pied flycatcher and the great tit take advantage of this. Their chicks hatch to coincide with this peak, so that there is enough food for them.’
‘Observations by biologists reveal that the caterpillar peak is currently three weeks earlier than it was in 1985. However, flycatchers and tits have not yet completely adapted – their chicks hatch about ten days earlier than in 1985. Warm-blooded animals have more difficulty in adapting to a changing climate than insects.’
‘Flycatchers spend the winter in West Africa. They take about three weeks to fly the five thousand kilometres here. When they are in Africa they cannot predict what the weather in Europe will be like – only if the circumstances are really bad en route will they break their journey.’
‘Nowadays, flycatchers appear to be arriving earlier in the Netherlands, which may be an evolutionary adaptation. By measuring exactly when individual ringed flycatchers arrive, we know that there are early and less early birds, and that the difference is inherited by the chicks. As a result of the shift in the caterpillar peak, the early birds currently have more food for their chicks and can raise more chicks. That means that the numbers of early birds have increased.’
‘This year, everything in nature has been delayed. This is to the advantage of the flycatchers which arrive a bit later. The chances are that these late birds will have more chicks this year than the early birds. The early birds are having a tough time – they started their migration early, but met bad weather en route. It is possible that more early birds die when the spring is long and cold – that’s what we’re going to learn in the next few weeks. All in all, this cold spring could delay the evolutionary adaptation of this species. This is the paradox of this situation – spring will now occur at the same time as thirty years ago, but that is bad for the species – the early adaptations will be set back years.’
‘Climate change is extremely interesting for biologists because we can then closely study how the process of adaptation works, and also the difficulties faced by the species which have to adapt.’
‘Global warming has a different effect on different parts of the entire food web. The caterpillars adapt much faster than the birds, which will therefore eat fewer caterpillars. That’s a good thing for the caterpillar, but could be very bad for the trees. If caterpillars eat the oak trees bare, they won’t produce any acorns that year, which is bad for field mice and wild boar.’
‘The differences between species in speed of adaptation could disturb a food web, but we hardly know anything about that at the moment. With my research I want to chart as many of the effects of climate change on the food web as possible, through observation and experiments in the woods.’
Christiaan Both (1969) of the University of Groningen is researching the effects of climate change on migratory birds and their environment. His fieldwork concentrates in particular on pied flycatchers in Drenthe and Africa.
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