Autumn is a time of change in the natural world. Summer’s screaming Swifts are gone, so too are the Turtle Doves, Pied Flycatchers and other migrant birds that brought song and life to our cities, farmland, woodlands and moorlands. These birds make incredible journeys. And it’s thanks to technology that we’re able to appreciate those journeys in some considerable detail – from the routes they take to the timings and strategies involved.
In celebration of World Migratory Bird Day on 12th October, we’ll explore some of the tech involved in tracking birds, some of the stories that tracking has helped uncover and how that information is being used to support further conservation work.
The importance of understanding migratory journeys
To help migratory species whose populations are in decline it is critical that we understand the routes they take and the habitats and locations they use during stopovers and in the non-breeding season. Without understanding their migratory routes we cannot investigate the threats and pressures that they face along those routes. Understanding how birds are moving along their migratory flyway is one of the first steps in identifying how best to help them. That’s where tracking comes in.
Tracking tech
Technological advances have opened the doors to discovering much about the birds that visit us. When it comes to tracking birds, there are a number of options including:
Satellite tags. These transmit data in near real-time so we can follow individuals. As they transmit information they tend to be larger than the other options but can weigh as little as 2g.
GPS tags. Depending on their size, these can sometimes transmit data but the smallest tags must first be retrieved to offload data. These can weigh as little as 1g.
Light level geolocators. These are tiny (weighing as little as 0.3g). Locations are estimated from light levels which indicate times of sunset and sunrise and are less accurate compared to satellite and GPS tags.
All bird capture and tagging is strictly licensed to ensure safety without negatively impacting on the birds.
Satellite tags and Turtle Doves
The UK’s breeding Turtle Dove population has experienced severe declines in recent decades. To understand more about this migratory species and how best to help it, many research techniques have been employed – from investigating how to provide the birds with the seed food they need on their breeding grounds to satellite tagging to learn about the routes they take and where they spend the winter.
Thanks to this work, we now know much more about Turtle Dove migration. In autumn, UK-breeding Turtle Doves travel south via France and Iberia, crossing into Africa via Morocco before continuing south across the Sahara. They spend our winter across the floodplains of the Senegal, Niger and other rivers in Senegal, Gambia, Mali and Mauritania. In spring, they move north again, following a similar route in reverse. This work was carried out with researchers at the Office National de la Chasse et de la Faune Sauvage in France, combining data on birds breeding in the UK, France and Senegal. Find out more on the Operation Turtle Dove website.
The information provided by Turtle Dove migration tracking has proved invaluable in helping this special visitor. Knowledge of the migratory routes of Turtle Doves in Western Europe has been used to inform efforts to tackle unsustainable levels of Turtle Dove hunting. Since 2021, temporary hunting bans have been put in place in France, Spain and Portugal, effectively saving the lives of around one million Turtle Doves from Western Europe every year, including birds from the UK. The whole breeding population of Turtle Doves across Western Europe (of which the UK population is a part), is now showing signs of recovery, with a rapid 25% increase in the population as a whole recorded in just two years since the temporary hunting ban began in 2021. As the UK sits at the northern edge of this much larger Western European breeding population, we expect the ‘recovery wave’ to reach us after a few more years.
Tracking has enabled us to identify where the UK’s breeding Turtle Doves spend the winter and carry out research on the wintering grounds to learn about the habitats the birds use – such as grasslands, farmland and Acacia thickets. To date, we have not identified any significant threats to these habitats on the wintering grounds. Extensive research on the breeding grounds clearly shows that a lack of seed food here in the UK has been the main driver of Turtle Dove population declines – with fewer seed-bearing wildflowers and weeds available owing to changes in agriculture. Operation Turtle Dove, a partnership project between the RSPB, Natural England, Pensthorpe Conservation Trust and Fair to Nature, is focussed on improving breeding season habitats for Turtle Doves by working with farmers and other land managers to help provide seed-rich feeding habitats as well as suitable nesting habitats and sources of water. You can find out more about Operation Turtle Dove here.
Turtle Dove © Ben Andrew (rspb-images.com).
GPS tags and Swifts
For a species that is almost constantly in flight, being able to use technology to track Swift migration is a significant step forward in our understanding where the birds go, and as a consequence, growing our knowledge of the potential challenges that this species faces.
The UK’s Swift population declined by 66% between 1995 and 2022. It is thought that a lack of suitable nesting sites is playing a part in the decline, however there could be other drivers of decline and that’s where understanding their annual migrations comes in.
In 2022, tiny GPS tags were used to understand the foraging behaviour of Swifts when feeding their young but some birds were also tracked on their annual migrations to Africa. This work showed that they migrated south via France, Spain and Portugal, crossing into Morocco and over the Sahara. They then headed south-east, spending a few months feeding over the rainforests of central Africa. By the beginning of the new year they had made their way to the coastline of east Africa where they spent the rest of our winter. By March they were making their way north once more, this time travelling via West Africa. From West Africa they returned via Iberia to the same nest sites used the previous year.
Over 10 months, one tracked Swift had flown over 26 countries and covered 15,000 miles (not including foraging) – an incredible feat. You can watch an animation of this journey below: https://www.youtube.com/watch?v=O1dyhNM6FUA
Understanding where Swifts migrate to is the first step in identifying any obvious threats along the way that could be contributing to their declines. Without tracking technology we would have far less information about where these birds spend two thirds of their year when they’re not in the UK.
Swift © Ben Andrew (rspb-images.com).
Geolocators and small migratory birds
Wood Warbler, Whinchat and Pied Flycatcher are three migratory species that have all undergone long-term population declines in the UK. To better identify how to help these declining species, conservation work has included identifying their migratory routes, understanding where they spend the non-breeding season and the habitats they use. All thanks to the tiniest of tracking devices, geolocators.
For Wood Warbler and Pied Flycatcher, tracking has helped us to identify specific areas within West Africa that the birds use over winter. When we know where they go, we can investigate potential threats to these wintering locations that may impact the birds.
We know that Wood Warblers use different habitats that include trees over the year, including within Africa. Our flyway conservation work in West Africa includes working with local partners to improve wooded savannah habitats on a landscape scale, one of the habitats Wood Warblers like. We have studied Wood Warblers in the Sahel and humid forest habitats of Africa and find a surprising resilience to loss of native forest cover but they show preferences for a few tree species for foraging, while avoiding some non-native tree species commonly planted by farmers. This knowledge helps us advocate for levels of tree cover including these favoured species.
Wood Warbler © Ben Andrew (rspb-images.com).
As a result of this work revealing that the birds wintered in a relatively small area of West Africa, we have been able to undertake fieldwork in Liberia to understand more about the species’ ecological needs and whether there are any threats impacting its wintering habitats.
Pied Flycatcher © Ben Andrew (rspb-images.com).
Knowing that the tracked Whinchats were spread far apart during the non-breeding season suggests that if something on the non-breeding grounds is driving their population declines then the threat must be very widespread, across the whole region, rather than in a particular location or habitat. It is therefore more likely that the threats in this case lie either on their migratory journeys, or on the breeding grounds. Find out more here.
Whinchat © Ben Andrew (rspb-images.com).
Technology is helping to uncover a wealth of information about some of the migratory birds that visit us. Piecing together where birds travel to and the timings of these journeys is helping us to understand where problems for these species lie, whether they be on the breeding grounds, during migration or on the wintering grounds.
Huge steps forward
Take a few moments to reflect on the incredible journeys migratory species make. Just a few short months ago, our skies were full of screaming Swifts and other migratory birds and now these birds have flown thousands of kilometres south and will spend the winter months south of the Sahara.
It’s thanks to tracking technology that we can know so much about the journeys these birds make. And it’s thanks to our members, supporters and partners we can continue our work to help these remarkable birds.
Our work to help migratory birds includes working with partners on the East Atlantic Flyway – a bird superhighway that stretches from the Arctic to the southern tip of Africa. You can read more about this work in the following blog posts:
Acknowledgements
Much of this scientific research has been carried out with partners and institutions, including: BTO, Devon Birds, Office National de la Chasse et de la Faune Sauvage, Natural England, NERC, University of Exeter.
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