Earlier migration shows how some species are responding to climate change

As the world’s climate changes, plants and animals are being exposed to new environmental conditions, including changes to the timing of seasons. This has a knock-on effect in the timing of periodic events such as flowering in plants and breeding in animals.

According to researchers studying how these events are impacted by climate – a field known as phenology – one example of this is in migratory birds. In recent years studies have suggested that birds are arriving at their northern hemisphere breeding grounds earlier as a result of global climatic changes.

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‘We are not considering human interference at this stage, but the practical outcomes may be human interference.’

Dr Luis Cadahía of the University of Oslo, Norway, led the EU-funded BIRDCLIMCHANGE project, which studied the effect of changes in climate on bird migration. He analysed 30 years’ worth of data from a Norwegian population of pied flycatchers, a migratory bird presumed to winter in west Africa.

‘We were interested in the migration phenology (of the pied flycatchers), the migration dates, whether or not they actually migrate later or earlier than they used to, and trying to link that with climate or climate change,’ he said.

‘The main thing we found was that the migration phenology of these birds advanced by almost five days. Meaning that if you look at the dates they arrive in Norway after spending the winter in Africa, they now arrive almost five days earlier than they did in the 1980s.’

Migration mismatch

According to Dr Cadahía, this change in migration timing could be problematic because it could result in a mismatch between arrival dates and favourable conditions at the Norwegian breeding grounds.

‘If they arrive too early, for example, because conditions throughout their journey have been good, but that improvement in conditions hasn't happened in Norway, they will arrive in a place maybe covered in snow, with scarce food,’ he said.

‘On the other hand, if they arrive too late they will miss the peak of food availability and their fecundity (annual reproductive rate) may be lower, so instead of, for example, laying an average of six eggs they will lay four or three.’

Migratory birds are particularly susceptible to climatic changes for two related reasons. They split their year between different locations that are thousands of kilometres apart and climate change is not consistent between those places.

Dr Cadahía explained: ‘Climate change does not happen equally around the globe, it is not like temperatures are just rising everywhere. It is more complicated, temperatures and rainfall patterns are changing in different areas, but not in a similar way.’

Analysis revealed that the pied flycatchers’ earlier spring arrival is as a result of a trade-off between the effects of climate conditions at migration stopover points in southern Europe and their Norwegian breeding grounds.

The researchers found that in years with an early spring, increased food availability in southern Europe causes the birds to spend longer than usual at migratory stopover points. If this was the only factor, in warmer years they would arrive in Norway later.

Early arrival

However, in warmer years, when the weather is also wetter in Norway, the flycatchers actually arrive at their breeding grounds earlier. This is because in southern Norway, the low-pressure systems that bring rain and higher temperatures also involve southern winds that act as tail-winds for the flycatchers, speeding up the last stage of their migratory journey.

Climate data shows that over the last three decades average temperatures and rainfall in southern Norway have both increased, corresponding with the earlier arrival of the pied flycatchers at their breeding grounds.

In the future, Dr Cadahía hopes to investigate whether the change in migration dates has resulted in any genetic changes in the pied flycatcher population.

While birds are responding quickly to changing conditions, at the other end of the scale scientists are concerned that trees may struggle to cope with the rapid climate change we are currently experiencing.

‘These concerns are due to the fact that trees are long lived species and they may not be able to adapt because their generation length will not allow them to,’ explained Dr Antoine Kremer, principal investigator of the TREEPEACE project, funded by the European Research Council.

While previous studies have looked at the potential impacts of climate change on forests, little attention has been given to the evolutionary responses of the different types of trees within the forest. The TREEPEACE project, which started in February 2014, aims to address this.

The project will examine the pace at which evolutionary change has taken place in trees during past and present periods of climate change, using European temperate oaks as a case study. It will focus on three different time periods, tracking environmental change and comparing oak DNA from each one.

The first time period will cover trees that were alive just after the last glacial period, around 12 000 years ago, when the global climate changed very rapidly. The second will cover trees that are alive today and lived through Europe’s ‘little ice-age’ around 300 to 400 years ago. The third time period will look at trees that are approximately 50 to 100 years old.

TREEPEACE researchers will use the data they collect to work out the past and present evolutionary pattern of the trees, and develop a model to predict how they will respond to future pressures, including human-influenced climate change.

In extreme situations, this information could even be used to inform intervention programs to help ensure the survival of tree species and maintain biodiversity.

‘We are not considering human interference at this stage, but the practical outcomes may be human interference,’ Dr Kremer said. ‘For example, if our predictions, or other predictions, show that trees may not be able to adapt then (scientists) may recommend assisted migration, moving material around, moving species, taking them from southern climate and artificially moving them to northern climates.’