World Migratory Bird Day - migratory birds and insects

To mark this spring’s World Migratory Bird Day on 11 May, and its theme this year of ‘insects’, we are celebrating the incredibly important relationship between insects and some of our best-loved migratory birds.

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A Barn Swallow perched with an insect in its mouth.
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Insects and other invertebrates are such an important component of the rich variety of wildlife that we are privileged to live alongside and we are working to protect many rare insects and other invertebrates both in the UK and overseas. But today we’re focussing on the role that insects play in the lives of the migratory birds that visit us. Whether being eaten as prey themselves, propping up food chains, or contributing to the health of entire ecosystems, insects play a vital role in driving and supporting the long-distance international phenomenon that is bird migration.

A vital food source

We’ll start with a migratory species whose name demonstrates just how important insects are to it – the Pied Flycatcher.  

Head out to a mature upland oak woodland in Wales, northern, central and western England in spring and you might be lucky to come across this small, Robin-sized bird. The males of which are black and white and the females a softer brown and white. They nest in holes in trees as well as nest boxes. And their principal food source? Insects. They catch insects in the air as well as picking up caterpillars and other invertebrates on leaves and branches. Hence the name ‘flycatcher’. 

Despite their size, Pied Flycatchers make an impressive migration from our Atlantic oak woodlands to the forests of West Africa, to a relatively small region encompassing Guinea, Sierra Leone, Liberia and Cote d’Ivoire. How do we know this? RSPB scientists and other researchers have fitted tiny tracking devices to Pied Flycatchers when they’re here in the UK.  

Understanding more about the migratory journeys these birds take helps us to determine how best to support them. Work on RSPB reserves to conserve and restore precious breeding habitat in the UK will help to protect their breeding habitats – as demonstrated in 2023 which saw record-breaking numbers of Pied Flycatchers at some RSPB reserves. And working with partner organisations and in important landscapes along the East Atlantic flyway helps to protect important habitats for a range of migratory birds. For instance our work in the Gola Rainforest of Liberia and Sierra Leone is helping to protect habitats for migratory species, some incredible resident wildlife and the livelihoods of the people that live in and around the forest.

Pied flycatcher perched on a branch with food.

Bugs in the food chain

Insects are not only important for migratory birds as a direct source of food, they also play a vital role in the wider food chain that supports these birds.  

Picture the scene; it is spring in Scotland’s Cairngorms National Park and you gaze across the glassy calm waters of a loch. Suddenly the still surface is pierced by two taloned feet and the body of a majestic hunter. After a 6,000 km journey north from the warmth of West Africa, the Ospreys are back; and it is insects that make this journey so worthwhile.

Osprey in flight over a lake.

Extinct in the UK as a breeding bird by 1916 due to persecution, Ospreys naturally recolonised in the 1950s and their recovery, which first began at our Loch Garten/Abernethy nature reserve, has been closely monitored for over 60 years by the RSPB and our partners, beginning with the pioneering Operation Osprey’ project. There are now thought to be more than 300 breeding pairs in the UK each summer and you can even follow the lives of our Abernethy birds 24/7 on a livestream.

The early days of ringing Osprey chicks at Loch Garten.

Underpinning their recovery has been the availability of fish in our lakes and rivers for the adult birds to feed to themselves and their chicks during the breeding season. Crucially, it is in summer that the larvae of mayflies, caddisflies and many other species, which have been developing in deeper waters, rise to the surface take flight in their adult form. This abundance of insect prey draws fish like trout closer to the surface where they in turn present a ready meal for a hungry Osprey.

Pollinators are key

We now come to a migratory species that you might not think of when you think of a bird that needs insects. It’s the Turtle Dove.

Turtle Dove perched in hawthorn.

Turtle Doves are seed-eaters, they don’t eat insects. So what’s the link? Pollination. Many of the seeds that these pretty migratory doves eat, from plants like fumitory or clovers, are mainly produced because the flowers are pollinated by insects.  

Turtle Doves migrate to us in spring, making an incredible journey from Africa to our shores. We know that one of the key things needed to help the UK breeding Turtle Dove population to recover is to ensure they have a plentiful supply of plants that provide the small seeds they need. That’s why Operation Turtle Dove is working with farmers and other land managers to help them to create feeding habitats for the birds.  

Turtle Doves need pollinators but at the same time, by providing pollen and nectar-rich plants in the countryside, people who are managing land for Turtle Doves are also providing pollinators with a good supply of the flowers they need. It’s a win-win situation.

The impact of insect declines

As you can see, insects are so important to migratory birds – not just the species we’ve mentioned here but so many other familiar favourites like the Swifts and House Martins that bring joy to our summer skies. 

Many migratory bird species are in trouble, but so too are the insects that they rely on. For instance the State of Nature report found that the distribution of pollinating insects in Great Britain had declined by an average of 18% since 1970. 

Declines in insects can only be a further challenge to the migratory birds that rely on them. Take the Cuckoo for example. Cuckoo numbers declined by 34% between 1995 and 2000 in the UK but the decline has not been consistent, in England numbers have fallen strongly, whereas in Scotland Cuckoos have actually been on the rise. There may be a number of factors involved in these changes but there is evidence to suggest that a loss of insects may be playing a part. Cuckoo numbers have fallen more in those habitats where their insect food (large hairy moth caterpillars) have also experienced the strongest declines. It’s a fascinating and worrying link (find out more here) and just goes to show how important insects are in the lives of the much-loved migratory birds that visit us each year and how important conservation work to restore and protect wildlife-rich habitats is.

Cuckoo perched on a branch.

Giving migratory species a helping hand

The UK sits on a bird migration superhighway known as the East Atlantic Flyway. We’re working in the UK to protect and create good habitat for migratory species and we’re also working with partners along the flyway, from Iceland to South Africa, including working to restore habitats in northern Ghana and protect the Gola Rainforest of West Africa. By working across this flyway we can help these birds when they’re here and further afield.

Get involved

If you have access to a garden or greenspace you can support insects, birds and other wildlife by following some of these handy guides:  

And don’t forget that taking part in citizen science projects, like Big Garden Birdwatch or those of other organisations such as the Big Butterfly Count can help us to understand how our wildlife is faring.  

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