Bird migration worldwide was probably as important during the last ice age as it is today, according to a global model reconstructing migration patterns over the past 50,000 years published in Nature Communications . The findings suggest that this phenomenon is older than was previously thought.
Many bird species migrate in response to seasonal variations in climate. This behaviour can be flexible; for example, some species have already altered their routes to cope with ongoing climate change. As seasonality was less pronounced during the ice ages, it has been proposed that bird migrations were far less important during these periods than today.
Marius Somveille and colleagues show that birds are likely to have remained migratory throughout the last 50,000 years. The authors used a model that simulates the seasonal geographic distributions of birds across the world based on energy efficiency (the interplay between access to resources and the energetic cost of travelling). After validating the model using the known distribution of almost all non-marine bird species alive today (9,783 species), it was combined with past climate reconstructions. According to their simulations, bird migration remained globally important despite major climatic changes between the last glacial maximum (around 20,000 years ago) and the current interglacial period. However, there were notable regional variations; for example, in the Americas fewer species migrated during the last glacial maximum than do so today.
The authors conclude that the simulations provide a baseline for predicting how bird migrations may respond to future climate change.
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