MI­GRA­TION MYS­TERY

State-of-the-art tech­nol­ogy used to mon­i­tor birds will al­low ex­perts to learn more about mi­gra­tion and how we can safe­guard their future sur­vival

Bird Watching (UK) - - Marvels Of Migration - WORDS: RICHARD SMYTH PHO­TOS: RSPB AND BTO…

WE ALL KNOW how easy it is to lose track of a bird. The elu­sive war­bler that van­ishes between one tree and the next; the uniden­ti­fied seabird for­ever just dis­ap­pear­ing over the hori­zon. So imag­ine how dif­fi­cult it is to keep tabs on a bird – let alone dozens of birds – when it is head­ing out into the freez­ing ex­panses of the North At­lantic, or plung­ing into the steamy un­der­growth of sub-sa­ha­ran Africa.

How to solve the prob­lem? Well, we can al­ways ring birds, and see where they end up.

“There was only one re­cov­ery of a ringed Cuckoo in Africa,” points out Chris Hew­son of the Bri­tish Trust for Or­nithol­ogy (BTO). “That was in 1928, re­cov­ered in Cameroon.” He adds that the find­ing ac­tu­ally set us off on the wrong track: for a long time it was thought that the birds win­tered in Cameroon, when in fact the Cuckoo in ques­tion was prob­a­bly al­ready head­ing north­wards, back to its Euro­pean breed­ing grounds, when it was caught. Chris is head­ing up a pro­gramme of bird­track­ing projects de­signed to bring the lat­est in 21st Cen­tury tech­nol­ogy to bear on this most en­dur­ing of prob­lems. Since 2011, the BTO has been de­ploy­ing satel­lite tags to mon­i­tor the move­ments of Cuck­oos as they head to their African win­ter­ing ter­ri­to­ries. The tags trans­mit sig­nals to the Ar­gos satel­lite network, which re­lays the in­for­ma­tion to a ground-based com­po­nent that is able to use a wave­length phe­nom­e­non known as the Dop­pler ef­fect, which serves to cal­cu­late the birds’ ap­prox­i­mate lo­ca­tions.

It’s a lot of trou­ble to go to for a hand­ful of birds. What’s it all for?

“The main driver is the big de­cline we’ve seen in Afro-palearc­tic mi­grants,” Chris ex­plains, “par­tic­u­larly those that go fur­ther south than the Sa­hel, those that go into the hu­mid trop­ics of western and cen­tral Africa. In a lot of cases, we knew very very lit­tle about what our birds did, cer­tainly once they left Europe and, in some cases, once they left Bri­tain. “So, if we were to have any chance of find­ing out what’s go­ing on with these birds in terms of their pop­u­la­tion de­cline, we re­ally needed to know a lot more about what they were do­ing through­out the rest of the year when they’re not here on their breed­ing grounds.”

The summer of 2016 saw eight new birds – from Sher­wood For­est, the New For­est, Thet­ford For­est and Dart­moor – join­ing the BTO’S corps of tagged Cuck­oos, which now num­ber 12 in to­tal. The data sent back from the tags (which are fas­tened between the bird’s wings, ‘like a lit­tle back­pack’) will help Chris and his team gain a more com­plete un­der­stand­ing of the threats fac­ing the species. Twelve birds is a big enough sam­ple for what the BTO’S Cuckoo Project is hop­ing to achieve, as Chris ex­plains: “If you’re try­ing to get a gen­eral idea of what the over­all mi­gra­tion strat­egy is, then the gen­er­ally con­sid­ered min­i­mum is about four birds.”

There are dif­fer­ent ap­proaches to tag­ging birds

But other kinds of project re­quire a more widescreen ap­proach. The RSPB’S seabird track­ing project, launched in 2010, has so far mon­i­tored the move­ments of some 1,200 in­di­vid­ual birds from 27 breed­ing colonies. “The RSPB got Euro­pean fund­ing from the Future of the At­lantic Ma­rine En­vi­ron­ment (FAME) pro­gramme, and that al­lowed us to start the big­gest track­ing project that has ever been un­der­taken in the UK,” says RSPB Con­ser­va­tion Sci­en­tist Dr El­lie Owen. El­lie’s part of the project was de­signed to ad­dress the big­gest data gap in our knowl­edge of seabird move­ments: where the birds go to feed dur­ing the breed­ing sea­son. Be­fore the ad­vent of high-tech tags, re­searchers re­lied on in­di­rect meth­ods to es­ti­mate the birds’ for­ag­ing ranges – look­ing out for birds at sea car­ry­ing fish land­wards, for in­stance, or tim­ing the birds’ trips to and from the nest. Tag­ging has rev­o­lu­tionised the field. “The data was break­ing all the rules straight away,” El­lie says. “Birds were for­ag­ing fur­ther from the colony than any­one thought pos­si­ble, and seabirds of the same species at dif­fer­ent colonies were trav­el­ling very dif­fer­ent dis­tances.

The data was break­ing all the rules straight away,” El­lie says. “Birds were for­ag­ing fur­ther from the colony than any­one thought pos­si­ble, and seabirds of the same species were trav­el­ling very dif­fer­ent dis­tances

“Some were able to feed on their doorstep, while oth­ers had to travel hun­dreds of kilo­me­tres, prob­a­bly be­cause of a failure of food re­sources near the colony.” The study – which ini­tially cov­ered Ra­zor­bill, Guille­mot, Ful­mar, Kit­ti­wake and Shag pop­u­la­tions at 30 UK colonies – found an in­verse cor­re­la­tion between the dis­tance birds had to travel and their rates of breed­ing suc­cess. Af­ter six years of study, the team now has what El­lie calls a ‘gap-free map’ of where four of the target species are likely to be ac­tive dur­ing the breed­ing sea­son. It’s hoped that the map will be used in assess­ing the po­ten­tial im­pacts of off­shore de­vel­op­ments – wind farms, say, or gas plat­forms – as well as in helping to iden­tify op­ti­mum lo­ca­tions for Ma­rine Pro­tec­tion Ar­eas (MPAS). The miss­ing species is the Ful­mar. The track­ing project used tags that had to be re­cov­ered, so re­searchers had to re-cap­ture the target bird in or­der to ac­cess the data. Ful­mar are tricky birds to catch, and not just be­cause of their habit of vom­it­ing fishy fluid over their cap­tur­ers. “Once you’ve been work­ing with Ful­mars for a while, you work out how not to get cov­ered,’ El­lie laughs. ‘But the prob­lem is that they go on re­ally long trips.”

Tags are prob­lem­atic and many are li­able to be lost

The tags used on the birds are only tem­po­rary, and are li­able to fall off; the win­dow of op­por­tu­nity for

cap­tur­ing a re­turned Ful­mar be­fore the tag comes loose can there­fore be very small. In some cases, as many as two-thirds of tags go un­col­lected. El­lie talks me through the cap­tur­ing process for cliff-nest­ing species. It’s ac­tu­ally very sim­i­lar to the method used for cen­turies by the peo­ple of St Kilda, who re­lied on seabirds for their sur­vival – “we use the new­est tech­nol­ogy, but the old­est tech­niques,” El­lie says. A re­searcher, safely roped, will ap­proach the cliff-edge and lower a long pole to­wards the target bird. The pole has a loop on the end, which is used to en­snare the bird. It’s tricky, painstak­ing work – es­pe­cially for re­cap­tures, when the bird has been through the same process just days be­fore. “They know ex­actly what you’re do­ing,” El­lie said, though the ad­vance of tech­nol­ogy prom­ises to make life eas­ier for both the re­searchers and the birds. GPS tags that re­lay data to a ra­dio bases­ta­tion – and there­fore needn’t be re­cap­tured – have been suc­cess­fully used on Puffins and also Black Guille­mots. But progress comes at a price: the new tags can cost up to 10 times more than the old ones, while satel­lite tags like those used in the BTO’S Cuckoo project can set you back more than £2,000. New ground is al­ways be­ing bro­ken, es­pe­cially with re­gard to minia­tur­i­sa­tion. Tiny ge­olo­ca­tors, which are small enough to fas­ten to a leg-ring and mon­i­tor light lev­els to pro­vide a lo­ca­tion to a pre­ci­sion of around 150km, have long been in use, but now GPS – which is up to 10,000 times more pre­cise – is catch­ing up. De­vices weigh­ing just 0.23g have been at­tached to 10g Wood War­blers; El­lie’s team has been Gps-tag­ging Storm Pe­trels, which is the UK’S small­est seabird. Chris Hew­son is pas­sion­ate about the wider im­pacts of the BTO’S tag­ging pro­grammes. “It’s been re­ally im­por­tant for pub­lic en­gage­ment, rais­ing aware­ness of mi­grant de­clines,” he says. “In do­ing that you’re re­mov­ing im­ped­i­ments to future re­search and also the con­ser­va­tion ac­tion that needs to be taken. “Peo­ple aren’t go­ing to care about what they don’t know about. It’s part of the process of try­ing to raise the pro­file of mi­grants and mi­grant de­clines,” he added. The Cuckoo project, he said, has been the Trust’s most im­por­tant so far. The ad­vanced tech­nol­ogy in use has been a game-changer.

Data is king for mon­i­tor­ing birds

Al­mut Sch­laich, a re­searcher at the Uni­ver­sity of Gronin­gen who works on track­ing the threat­ened Mon­tagu’s Har­rier, is an­other evan­ge­list for satel­lite tag­ging. “[Satel­lite] bird tag­ging is the tool to fol­low birds year-round,” she says. “With mon­i­tor­ing and ra­dio-track­ing you can gain im­por­tant in­for­ma­tion on pop­u­la­tions and move­ment dur­ing the breed­ing sea­son, but where birds spend the rest of the year,

De­vices weigh­ing just 0.23g have been at­tached to 10g Wood War­blers; El­lie’s team has been Gps-tag­ging Storm Pe­trels

which routes they use for their mi­gra­tions, where they stop over, where they winter, can only be fol­lowed by us­ing track­ing de­vices,” she added. “The data that we re­trieve gives us in­for­ma­tion on pop­u­la­tion-spe­cific routes, con­nec­tiv­ity between breed­ing and win­ter­ing ar­eas, stop-over sites. An­other very im­por­tant thing is that we see where birds die dur­ing the an­nual cy­cle.” Al­mut says this is very im­por­tant to in­fer bot­tle­necks for a pop­u­la­tion. But Gps-log­ging tags which link to a ground­based an­tenna sys­tem rather than a satel­lite also have their uses. “Nor­mally, we build up a network of an­ten­nas in the breed­ing area that tagged birds con­nect to when they ar­rive back,” Al­mut says. “The ad­van­tage of these data is that you col­lect very de­tailed move­ment and be­havioural data (up to a po­si­tion ev­ery three sec­onds), and with this we can an­a­lyse habi­tat use on a much smaller scale,” she added. “This is needed to un­der­stand how birds use the land­scape and to in­ves­ti­gate which mea­sures could help them sur­vive and breed suc­cess­fully.” The em­pha­sis on tech­nol­ogy might sug­gest that bird re­searchers risk be­com­ing desk-bound lap­top-jock­eys, for­ever chained to data feeds and satel­lite link-ups. Far from it! Al­mut’s re­search has taken her far from the UK and the Nether­lands, to the har­ri­ers’ reg­u­lar win­ter­ing grounds in the Sa­hel re­gion of Africa. “It’s one thing to see the tracks on a map, which is al­ready amaz­ing, but an­other to see the birds from so close by, fol­low them down to their stop-over sites in east­ern Morocco and their win­ter­ing ar­eas in Niger, Burk­ina-faso, Mali and Sene­gal, and see­ing the same birds you held in your hand some months be­fore fly­ing over the sa­van­nah land­scape hunt­ing grasshop­pers! Just amaz­ing,” she says. “The com­bi­na­tion of track­ing data and field­work is the key to find­ing out more about the re­quire­ments of the species.” Sim­i­larly, El­lie Owen from the RSPB first ex­pe­ri­enced the won­ders of track­ing data at one of the UK’S wildest spots, the is­land of Copin­say, east of Orkney. “In­cred­i­bly ex­cit­ing,” she re­calls. “Just an amaz­ing place: there are enor­mous waves right next to you, and you’re right be­low thou­sands and thou­sands of Ra­zor­bills and Guille­mots and Kit­ti­wakes, and add to that the fact that the data we were get­ting back was show­ing some­thing com­pletely new… “Ev­ery time we went through the tur­moil of ‘will we catch this bird back?’, ‘did the tag work?’ – then you fi­nally get this data pop­ping up – and it’s pretty cool.” For more about the BTO visit bto.org and for the RSPB visit rspb.org.uk

Which routes they use for their mi­gra­tions, where they stop over, where they winter, can only be fol­lowed by us­ing track­ing de­vices

BACK­PACK COM­PACT A to­tal of 12 Cuck­oos have been tagged by the BTO. The tags are fas­tened between the bird’s wings Tech­nol­ogy used to trans­mit in­for­ma­tion to the BTO is packed into a de­vice no larger than a 50p piece

BIRD TRACK­ING Chris Hew­son of the BTO is head­ing up a pro­gramme of projects us­ing the lat­est tech­nol­ogy to track birds, such as the Cuckoo

ON THE MOVE A Puf­fin in flight has been fit­ted with a tag and is be­ing mon­i­tored by the RSPB

LIGHTWEIGHT Some tags weigh as lit­tle as 0.23g and have been fit­ted to 10g Wood War­blers

TAG­GING Puffins are tagged to help re­searchers mon­i­tor pop­u­la­tion and move­ment

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