Over the last decade, many papers have been published showing how bird species’ distributions are projected to shift because of climate change. These find that for many species, the areas with suitable climate are expected to move towards the poles.
Some species that breed in northern temperate zones and winter further south will therefore need to undertake longer migratory journeys. However, no-one has previously looked at what this might mean in relation to the time and energetic costs of migration.
We collaborated with experts at Durham University and elsewhere to address this issue.
Why does climate change impact migratory birds in particular?
Migratory species require suitable conditions throughout their annual cycle: on their breeding grounds, in their non-breeding range, and along migratory routes between the two. Climate change has the potential to disrupt conditions in all three stages.
How did you arrive at your conclusions?
We used data on wing morphology and body mass to estimate the distance that individuals of different migratory species can fly before they need to stop to refuel. We combined these estimates with information on the length of migratory routes currently and in future, under projected climate change. From this we worked out the number of stop-overs individuals would need to rebuild their fat reserves, and hence the time required to migrate.
What did you find?
For over 80% of European long-distance migrants, there will be significant increases in both the distance and time taken to travel between their breeding and non-breeding ranges. For example, we estimate that Thrush Nightingales Luscinia luscinia will have to travel nearly 800 km further on average by 2070, adding at least five days to the duration of their journey. European Bee-eater Merops apiaster migrations are projected to increase by over 1,000 km and at least 4.5 days by 2070.
What are the implications for conservation?
Birds suffer higher mortality on migration, because of increased risk of predation and starvation resulting from higher energetic requirements and unpredictable food supplies. Longer journey increase these risks, and may therefore lead to population declines. Our study provides further evidence that long-distance migrants may be hit particularly hard by climate change.