Arctic tern's epic journey mapped

The Arctic tern's extraordinary pole-to-pole migration has been detailed by an international team of scientists.

The researchers fitted the birds with tiny tracking devices to see precisely which routes the animals took on their 70,000km (43,000 miles) round trip.

The study reveals they fly down either the African or Brazilian coasts but then return in an "S"-shaped path up the middle of the Atlantic Ocean.

The long-distance adventure is described in the US journal PNAS.

"From ringing, we knew where the Arctic tern travelled," said Carsten Egevang of the Greenland Institute of Natural Resources.

After setting out (yellow line) the birds pause in the North Atlantic (red circle) to feed. Going home (orange line), they follow the winds Total distance travelled 70,900km On southbound leg: 34,600km Daily progress south: 330km On northbound leg: 25,700km Daily progress north: 520km Within Winter grounds: 10,900km

"The new thing is that we've now been able to track the bird during a full year of migration, all the way from the breeding grounds to the wintering grounds and back again."

The avian world is known for its great migrations.

Albatrosses, godwits, and sooty shearwaters all undertake epic journeys. But none can quite match the Arctic tern's colossal trip.

Starting in August and September, this small bird - which weighs little more than 100g (3.5oz) - will head away from Greenland with the intention of getting to the Weddell Sea, on the shores of Antarctica.

It will spend about four or five months in the deep south before heading back to the far north, arriving home in May or June.

A team from Greenland, Denmark, the US, the UK and Iceland attached small (1.4g/0.05oz) "geolocators" to the animals to find out exactly where they went on this polar round trip.

The devices record light intensity. This gives an estimate of the local day length, and the times of sunrise and sunset; and from this information it is possible to work out a geographical position of the birds.

The geolocators were provided by the British Antarctic Survey (BAS).

"The use of these devices on seabirds is not only revolutionising our understanding of migration patterns, but the resulting data on distribution also help address the requirement to identify important biological hotspots," said Richard Phillips from BAS, a co-author of the PNAS paper.

With such a small bird, the trackers also need to be tiny

The first surprise is that the terns do not make straight for the Antarctic when they leave the Arctic, but make a lengthy stop-over in the middle of the North Atlantic, about 1,000km (620 miles) north of the Azores.

Here, they feed on zooplankton and fish to fuel themselves for the long journey ahead.

"We were able to compare biological productivity in the ocean from satellite imagery and we could see a high productive area that the birds will spend time in," said Mr Egevang.

"Even more importantly, it's the last high productive area before they enter tropical waters where we know productivity is low."

THE LONG DISTANCE FLIER Scientific name: Sterna paradisaea Average wingspan of 75-85cm Breeds in Arctic and sub-Arctic Lays eggs in small ground scrape Feeds on fish and crustaceans Birds live more than 30 years

The birds then head south along the coast of western Europe and western Africa before making a choice, either to continue hugging Africa or sweep across the Atlantic from the Cape Verde Islands to continue the journey along the Brazilian coast.

About half the birds that were tracked decided to take the South American path. It is not clear why, but the researchers believe wind might make either route seem favourable to the terns.

After spending their northern winter months in Antarctic waters, the terns then fly back towards the Arctic.

But rather than retracing their southward flight paths, the birds follow a gigantic "S" pattern up the middle of the Atlantic Ocean.

"This is completely new knowledge," Mr Egevang told BBC News.

"They make a detour of several thousand km but once we start comparing the route to the prevailing wind system, it makes perfect sense - moving in a counter-clockwise direction in the Southern Hemisphere, and clockwise in the Northern Hemisphere.

"It's just more energy-efficient for them to do that even though they are travelling several thousand more km than if they flew in a straight line."

Witch-doctors reveal extent of child sacrifice in Uganda

A BBC investigation into human sacrifice in Uganda has heard first-hand accounts which suggest ritual killings of children may be more common than authorities have acknowledged.

One witch-doctor led us to his secret shrine and said he had clients who regularly captured children and brought their blood and body parts to be consumed by spirits.

Meanwhile, a former witch-doctor who now campaigns to end child sacrifice confessed for the first time to having murdered about 70 people, including his own son.

The Ugandan government told us that human sacrifice is on the increase, and according to the head of the country's Anti-Human Sacrifice Taskforce the crime is directly linked to rising levels of development and prosperity, and an increasing belief that witchcraft can help people get rich quickly.

In the course of our investigation we witnessed the ritual torching of the shrine of a particularly active witch-doctor in northern Uganda by anti-sacrifice campaigners.

The witch-doctor allowed ceremonial items including conch shells and animal skins to be burned in his sacred grove after agreeing to give up sacrifice.

He told us that clients had come to him in search of wealth.

"They capture other people's children. They bring the heart and the blood directly here to take to the spirits… They bring them in small tins and they place these objects under the tree from which the voices of the spirits are coming," he said.

Asked how often clients brought blood and body parts, the witch-doctor said they came "on average three times a week - with all that the spirits demand from them."

We saw a beaker of blood and what appeared to be a large, raw liver in the shrine before it was destroyed, although it was not possible to determine whether they were human remains.

Extortion

The witch-doctor denied any direct involvement in murder or incitement to murder, saying his spirits spoke directly to his clients.

He told us he was paid 500,000 Ugandan shillings (£160 or $260) for a consultation, but that most of that money was handed over to his "boss" in a nationwide network of witch-doctors.

Three-year-old Mukisa had his genitals cut off by a witch-doctor In pictures: Children in danger

Head of the Anti-Human Sacrifice and Trafficking Task Force, assistant commissioner Moses Binoga of the Ugandan police, said he knew of the boss referred to - involved in one of five or six witch-doctor protection rackets operating in the country.

"The senior ones extort money from lower people because they deal in illegal things," he told us.

Mr Binoga said police had opened 26 murder cases in 2009, in which the victim appeared to have been ritually sacrificed, compared with just three cases in 2007.

"We also have about 120 children and adults reported missing whose fate we have not traced. We cannot rule out that they may be victims of human sacrifice," he said.

But child protection campaigners believe the real number is much higher, as some disappearances are not reported to police.

Activism

Former witch-doctor turned anti-sacrifice campaigner Polino Angela says he has persuaded 2,400 other witch-doctors to give up the trade since he himself repented in 1990.

Mr Angela told us he had first been initiated as a witch-doctor at a ceremony in neighbouring Kenya, where a boy of about 13 was sacrificed.

"The child was cut with a knife on the neck and the entire length from the neck down was ripped open, and then the open part was put on me," he said.

When he returned to Uganda he says he was told by those who had initiated him to kill his own son, aged 10.

"I deceived my wife and made sure that everyone else had gone away and I was with my child alone. Once he was placed down on the ground, I used a big knife and brought it down like a guillotine."

Asked if he was afraid he might now be prosecuted as a result of confessing to killing 70 people, he said:

"I have been to all the churches… and they know me as a warrior in the drive to end witchcraft that involves human sacrifice, so I think that alone should indemnify me and have me exonerated."

Uganda's Minister of Ethics and Integrity James Nsaba Buturo believes that "to punish retrospectively would cause a problem... if we can persuade Ugandans to change, that is much better than going back into the past."

Child protection activists in organisations such as FAPAD (Facilitation for Peace and Development) and ANPPCAN (African Network for the Prevention and Protection against Child Abuse and Neglect) have highlighted recent cases of ritual killing and called for new legislation to regulate so-called "traditional healers".

Witness testimony

In some cases against alleged witch-doctors due to come to trial later this year, police will use the testimony of children who managed to survive abduction.

One such witness is a three-year-old boy called Mukisa, who was left for dead after his penis was hacked off by an assailant.

He survived thanks to quick work by surgeons, and later told police he had been mutilated by a neighbour who is known to keep a shrine.

Mukisa's mother told us: "Every time I look at him, I ask myself how his future is going to be - a man without a penis - and how the rest of the community will look at him, with private parts that can neither be attributed to a man or a woman. Every time I recall the normal birth that I had and the way Mukisa is now, it is like the end of the world."