Combining almost 30 years of global cyclone and drought data with information on 383 fully migratory bird species, the research team behind the new study identified that 182 species were highly exposed to either cyclones or drought in either their breeding or wintering ranges, with an additional 67 species highly exposed to both types of events within a singular range.  

Senior author Professor Nathalie Pettorelli from ZSL’s Institute of Zoology said: “We cannot ignore how important migration is for global ecosystem health. These birds travel huge distances every year to raise chicks and survive the colder months, connecting ecosystems across the world. They provide vital ecosystem benefits including pest control and pollination of plants, while sometimes acting as key food sources for local wildlife.”  

Many geese and duck species move seeds and nutrients across countries and habitats, increasing plant diversity and increasing the fertility of local soils. Meanwhile, other species such as common swifts, seen soaring and darting across the British skies in spring and summer, provide insect control and crop protection in both their Eurasian breeding grounds and wintering grounds in Africa. However, they are also extremely exposed to drought; more than 95% of populations in both ranges have experienced extreme drought at some point in the last 30 years.  

The study further reveals that cranes, crakes, rails and nightjars were most commonly exposed to cyclones, while hawks, eagles, vultures and kites were most exposed to droughts. The eastern whip-poor-will (a mottled North American nightjar named after its whistling song) and the grey-faced buzzard (one of the only raptors to migrate over the ocean as it travels from breeding grounds in Japan and Korea to South East Asia) are particularly exposed to both events. 29% of the eastern whip-poor-wills wintering range has been hit by cyclones over the last 30 years, while almost all of the grey-faced buzzard’s breeding and wintering range has experienced drought over the same period. 

Pettorelli added: “These birds are also a source of delight for millions of bird watchers and enthusiasts around the world – and many species that we‘re used to seeing here in the UK, such as swifts, pied flycatchers and house martins, are already being exposed to these extreme events.” 

Lead author Rhys Preston Allen, a former student at ZSL’s Institute of Zoology who is now doing his PhD at Imperial College London, explained: “We are already seeing worrying declines in migratory species populations around the world. Birdwatchers across Europe have noted fewer songbirds returning from wintering areas each spring, year after year. 

“The journeys carried out by migratory species are a massive undertaking. Even so, migration is a vital survival strategy that evolved because the benefits – such as increased food availability – outweighed the costs. Unfortunately, this balance is shifting under escalating pressures from climate change and other threats, leading to less predictable ‘windows of opportunity’ along their migratory routes. This trend not only endangers the bird species involved, but also threatens the entire global network of ecosystems reliant on their migrations.”