European researchers have found that butterflies and birds are no longer able to keep up with climate change. According to the findings, birds are more than 200 kilometres behind the shifting climate zone, with butterflies 135 kilometres behind.

The research — in which Dutch Butterfly Conservation (De Vlinderstichting), SOVON Dutch Centre for Field Ornithology (Vogelonderzoek), Statistics Netherlands (CBS) and Wageningen University are taking part — is focusing on changes in the relative abundance of species in the total butterfly and bird community, where previous studies concentrated on individual species. The findings constitute the first evidence that climate change is causing entire groups of animals to accrue a 'climatic debt' on a continental scale. Over the last twenty years, this debt has risen to 135 km for butterflies and a staggering 212 km for birds.

In other words, butterfly and bird populations have a more northern character than one would expect on the basis of the climate. It is currently difficult to predict the long-term implications. The difference in the shifts between the two groups of species may disturb their interdependence. A good example of this is the Pied Flycatcher - Ficedula hypoleuca - whose young only hatch after the peak period for caterpillars in warm years.