Round-trip South Africa Northeast Greenland – a busy flier reveals its travel route
Long-tailed skua recaught at Zackenberg, Northeast Greenland – two years after fitting a light logger to the leg of this arctic migratory bird. The small logger contains detailed information on two trips back and forth from northern Greenland to southern Africa.
Back on the tundra at Zackenberg. The long-tailed skua NJ is here to breed and hatch a chick or two. It has arrived after a nearly 13,000 km long flight from the southernmost tip of Africa and has now found its way back to its childhood home where it was once hatched itself.
It is two years, almost to date, since the researchers for the first time caught the small skua and fitted a small light logger and an orange ring with the painted initials NJ to its right leg.
And now it is here again and has almost voluntarily given its small data box back to the scientists. A small box that, like the black box in an airplane, reveals the bird’s movements since it was fitted around its leg on 29 June 2012.
Cunning, dexterity and cheap bait
Well, “voluntarily” may not be exactly true. How do you catch a bird with the same size as a black-headed gull? The answer is use of cunning, dexterity and cheap bait.
Long-tailed skua is extremely difficult to catch. So far, it has only been done with success when the bird is nesting. For the purpose, the researchers may place a flap-net next to the nest and release it with a string. When released, the net falls over the nesting bird.
However, this year long-tailed skua has not started nesting at Zackenberg, Northeast Greenland. Perhaps it is yet too early and too cold. Or perhaps it is due to lack of food. It is well-known that the skua needs a rich diet of fat lemming – the small arctic rodent – to breed. When the number of lemming is limited, the bird postpones egg-laying until the next year where food in the meagre arctic larder is hopefully more plentiful. And as long-tailed skua may live for up to 20 years, it has time to wait.
This year, many signs indicate that this is a poor lemming year, and if the skua chooses not to attempt breeding it will soon fly south again. Therefore, time is pressing for the biologists at the Zackenberg Research Station to re-catch the skuas that they caught last year on their nests and fitted with small black boxes.
The biologists Jannik Hansen and Jannie Linnebjerg therefore chose to abandon the flap-net trap and use their own artistic skills instead. A plastic model of a magpie was painted over and fitted with a slender, long tail to look like a real long-tailed skua. And it does, at least if you are a small curious skua wanting to keep your territory to yourself.
If the artificial decoy on the ground is supplemented with a small loudspeaker playing sound recordings of another skua’s call, the temptation is almost too overwhelming. The stranger must be inspected.
And now comes the cunning plan – small pieces of chicken wire are fixed in the ground with solid pegs. On the top of the wire small loops – or snares – of thin fishing line are fastened, a job requiring great patience. It is almost impossible for a skua not to be tangled up in the snares when wading around with its large webbed feet.
And they were curious. The skua pair of which NJ is the male partner.
It took some time and some sweeps over the cheeky foreign bird before they landed to check it out. They approached it slowly and answered its call and very elegantly placed their feet outside the loops, to the great frustration of Jannik Hansen and Jannie Linnebjerg who followed each bird step at about 30 m’s distance through sharp binoculars. But finally NJ’s female partner had one of its legs caught in a snare.
Foul words were replaced by a loud “Yes” and four biologists scrambled across the arctic tundra, only to stop 5 m from the bird. Mrs. Skua flew freely into the semi-cold morning, which instantly would have been much warmer if four-letter words could be translated into heat.
To be so close and then not succeed! The two birds flew off and settled far away – but of course not too far away not to be annoyingly visible.
Two gram data collector
But curiosity is a difficult thing to control. And this strange bird – what was it up to?
The rest of the story is not difficult to figure out: they came back. Both of them. Again they dexterously avoided all snares until NJ was finally caught in one of the small, almost invisible loops. And this time – bingo. Jannik Hansen and Jannie Linnebjerg were on the spot and calmly extricated NJ from the snare only 100 m from the place where the small skua was caught two years earlier.
For two years NJ has flown with the small datalogger around its right leg. It weighs only 1.9 grams and every 5 minutes it records the hour and light status at the bird’s location. By combining the data, a computer program is able to track with great accuracy the route and resting places of the skua during its southward migration.
The datalogger has been checked. It is brimming with data that are now to be treated and thoroughly analysed. However, a quick glance at the information in the small data box confirms that the small skua flies all the way from Northeast Greenland to South Africa and back again for next year’s breeding season.
NJ brought data from two trips, and it appears that it has flown from Zackenberg in Northeast Greenland to the British Isles, continued to Portugal and further down the coast of West Africa, rounded the shores of South Africa and had a well-deserved rest in the waters surrounding Madagascar before it flew back north to the barren plains of Zackenberg. On the face of it, the bird seemingly followed the same route in both years, which remains to be confirmed by a more detailed analysis back in Denmark.
In total, the long-tailed skua flies up to 50,000 km in a year, this is more than round the world. Quite a performance by a bird weighing approx. 300 grams.
And perhaps NJ will already next year supply more details on the routes followed by the skuas and where they rest to fatten up during migration. Because before he was released, a new transmitter was fitted around his leg after which he flew off, settled annoyingly near and looked as if he thought: “What was that?”
Read also: (http://www.dr.dk/Nyheder/Viden/Naturvidenskab/2014/07/11130121.htm (in Danish)
Academic employee Jannik Madsen, Arctic Research Centre, Aarhus University. Biobasis.ZacBasis@skyfile.com, tel.: 00881641464327
Academic employee Jannie Linnebjerg, Arctic Research Centre, Aarhus University. Biobasis.ZacBasis@skyfile.com, tel.: 00881641464327
Senior scientist Niels Martin Schmidt, Arctic Research Centre, Aarhus University. email@example.com, tel. +45 87158683/+4541915664