Why are we tracking turtle doves?
Tracking turtle doves using small, lightweight satellite tags will not only tell us where birds that breed in the UK spend the winter but also, just as importantly, the routes they take to get to Africa, and the staging sites that they use.
This information, supported by more RSPB research in the UK and in Senegal in 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. The tags have a rechargeable battery charged by a solar panel.
To allow time for the batteries to recharge regularly, the tags 'rest' between transmission cycles. Titan’s tag was on a ‘10 hour ON, 48 hour OFF’; however, our new tags will transmit for 4 hours at a time and then rest for 19 hours. 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.
What precautions are taken to ensure the safety of the birds?
As with all work the RSPB does, the welfare of the birds is paramount.
This is not only driven by ethical concerns but also the realisation that if our actions affect the behaviour or survival of the birds, then our research could become invalidated.
The use of tracking devices, such as satellite tags, on birds in the UK is overseen by the Special Marks Technical Panel, an independent group of experts with many years' experience in the manufacture and use of such technology.
Before we were allowed to attach satellite tags to wild turtle doves, we were asked by the panel to trial the design of the harness on captive birds.
The particular harness that we chose was a braided nylon thoracic harness, identical to that used successfully on many species, including cuckoos by the British Trust for Ornithology, and fits a bird like a tiny rucksack.
A loop goes over the bird's head, and the loose strands are passed under the wings and reattached to the tag.
Our trials were two-fold: firstly, we tested whether wearing such a harness (along with added weight to replicate the tag itself) had any affect on the flight abilities of homing pigeons at lofts owned by Oxford University.
Secondly, we fitted harnesses to captive turtle doves kept at Pensthorpe Natural Park in Norfolk, to assess whether there were any physical impacts upon the birds, such as abrasions where the nylon is in contact with the skin.
The results of our trials were encouraging. The flight of homing pigeons was not impaired by the harness – flown in pairs and in groups, those fitted with the harness performed (in terms of speed, height and direction taken to the loft) just as well as those that were not.
Along with these pigeons, the captive turtle doves also showed no ill-effects of wearing the harness, even when they put on much pre-migratory fat and weight (a physiological response hard-wired into these captive birds).
The weight of the tag plus the weight of the harness material added up to around five grams, which ensured that it comprised less than three per cent of turtle dove body weight, an ‘industry standard’ when attaching devices to birds. Only after we had the results of all these trials were the Panel happy to give us permission to tag wild turtle doves last summer.
How did we catch and tag the birds?
Our specially trained and licensed researchers attempted to catch turtle doves at a number of sites in East Anglia, including RSPB reserves, farmland margins, and people's back gardens, using recognised safe trapping methods (mist nets and whoosh nets and walk-in traps, whereby the birds are attracted to bait within a small metal cage, and when safely in the trap the door is closed behind them).
Before fitting a tag, each bird is examined to check that it's healthy and strong; measurements, such as weight and wing length, are taken and its age and sex assigned based on plumage characteristics.
In addition to the tag, 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 has happened to the birds we have tagged?
In 2012, we fitted five turtle doves with satellite tags. All five were marked at sites used and regularly monitored by the RSPB turtle dove field research team.
However, none of these birds made it to the wintering grounds: one was lost on the breeding grounds, with evidence that predation was the cause of mortality. Contact was lost with three birds over Europe; one in Switzerland (itself, a strange route for a turtle dove to take), the others in France and Spain, countries known to provide serious challenges to migrating birds, such as adverse weather and hunting. The final bird made it to Africa, being lost in Western Sahara – a huge natural barrier and interestingly, very close to where a bird tagged by a French research team was lost the following year.
In 2014 we fitted satellite tags to two turtle doves, both of which remained in the vicinity of the breeding grounds until the third week of September, when both birds headed through France and into north-central Spain. From here, one of the birds flew towards the east coast, where we lost contact with it on 1 October.
The other bird, named Titan , became the first UK-breeding turtle dove to be tracked over the whole of its migratory journey, from Suffolk to West Africa and back again. We were also able to follow him for a second autumn / winter as he returned to Africa.
We have not heard from Titan since 22 April 2016, when he was still in Mali c.100km west of the capital Bamako.
In 2016 10 UK breeding turtle doves were fitted with satellite tags. Five of the birds were lost in the UK breeding grounds, with the indication of predation as the cause of mortality.
Bird 160999 was legally shot in autumn 2016 in Spain. The bird was recovered by SEO-BirdLife confirming it’s identity. This highlights just one of the threats facing migrating Turtle Doves as they travel across Europe.
The progress of the remaining birds can be followed on the map on our turtle dove tracking webpage.
We couldn't have carried out the tagging without the help of a large number of people.
Professor Tim Guilford at Oxford, Chrissie Kelley at Pensthorpe, Toby Collett at RSPB Frampton Marsh, Jon Gibbs, John Butt, Joe Martin, John Secker, Ian Archer, Roger Lawrie, Kim Bayfield, Ray Ellis, John Gibbs, Liz Wicken, Dave Fairhurst at RSPB Snape, Dave Thurlow at RSPB Aldringham Walks, Peter Harris, George Harris, Dave Smart at EWT Wrabness, Maureen Gibson, Graham Denney, John Walsh, Frances and Roland Bee, Doug Radford at RSPB Fowlmere and Andrew Holland.
Special thanks must be given to Heather Maclean, who kindly opened up her garden and house to us. Two birds were caught in her garden.
Sadly, Heather passed away in October 2014; to the end, she remained interested in what her birds were up to. A long-term RSPB volunteer, we hope that all we learn about turtle dove migration will be a fitting legacy for her and her long birding life.