Why are we tracking turtle doves?
Tracking turtle doves using small, lightweight satellite tags will tell us how far the doves travel to feed, how and where they migrate and where our birds spend winter.
This information, supported by more RSPB research in the UK and west Africa, is crucial to developing a plan to help turtle doves in all parts of their range.
Since turtle doves that breed in the UK spend only a third of their time here, learning more about the needs of birds on migration and in Africa directly helps their conservation in the UK. To save the turtle dove from extinction in the UK, we must know more about the issues that affect them while on migration.
How do the tags work?
The turtle doves are fitted with small satellite tags supplied by Microwave Telemetry Inc. that transmit information about their journey to RSPB conservation scientists via orbiting satellites, such as the Argos satellite. The tags have a rechargeable battery charged by a solar panel.
To allow time for the batteries to recharge regularly, the tags 'rest' for 48 hours between each 10-hour 'transmitting' period. When fully charged, the tags can also transmit at night or when the bird is under trees, for example.
Do the satellite tags affect the birds' ability to navigate?
There is no evidence that the transmitters cause navigation errors. The tag transmits infrequently and only at certain periods. Satellite tags have been used successfully for a number of years on a wide range of species, including by the RSPB on ospreys, white-tailed eagles, red kites, northern bald ibises and sociable lapwings.
Are the tags heavy for the birds to carry?
The tag weighs just less than 5 grams - about the same as a 20 pence piece. This is around 3 per cent of the turtle dove's body weight.
If the tags affected the birds' behaviour, it would make the research invalid, so we take great care in the design and fitting of these devices to ensure we stay within strictly controlled guidelines. Once a tag has been fitted, our researchers watch the tagged birds for up to three months and report that there are no differences in behaviour between tagged and untagged birds.
How are the tags attached to the birds?
Our specially trained and licensed researchers have been catching turtle doves at study sites in East Anglia using recognised safe trapping methods (mist nets and whoosh nets).
Before fitting a tag, each bird is examined to check that it's healthy and strong. The researchers take measurements - like the bird's weight and wing length – and from DNA testing, we'll also find out what sex the birds are. The birds' welfare and safety always comes first.
We ring each turtle dove with a British Trust for Ornithology lightweight metal leg ring to help identify them in future. The tag is attached to a harness that the bird wears, a bit like a tiny rucksack. Considerable thought and attention to detail has gone into the harness design. Tailoring them for each bird means we can get the best possible fit.
How long will the tags last for?
Once fitted to the turtle doves, and provided the battery is well-charged by the solar panel, each tag should last around two years.
Sometimes the tags don't work so well while the birds sit around in dense cover (for instance when they are on the nest or roosting in trees), but they shouldn't be short of sunlight once they head towards the Mediterranean and onwards to Africa.
What happened to the first five birds to be tagged?
We fitted five turtle doves with satellite tags in 2012. All five were marked at sites used and regularly monitored by the RSPB turtle dove field research team.
Three of the five were seen after being tagged on a number of occasions by RSPB staff between June-August 2012. No differences in behaviour (in flight, breeding or feeding) were noted between these birds and a comparison group of unmarked birds observed at the same places and nearby.
Though we lost contact with one bird on the breeding grounds (with signs that it was caught by a predator), the other four made long-distance movements of between 413 and 2,163 miles, suggesting that normal migratory movements were not impeded by the tag and harness.
The tags do not allow us to identify causes of mortality, though it is perhaps telling, and not at all surprising in a species facing so many threats to survival, that contact was lost with all of the five birds.
The bird passing through Switzerland was attempting to make a crossing of the Alps during a period of bad weather, whilst those heading down through France and Spain did so during a period when the species can be legally hunted.
As for the fifth bird, contact was lost as it passed through the Sahara - a huge natural barrier, and a forbidding place for a migrant bird.
We know that these threats to survival exist - what tracking does is allow us to focus our conservation actions far more effectively on precisely those areas the birds are using when they leave the UK.