The secret life of seabirds
They scoot the skies, and ride the waves, journeying far into a salty wind.
Birds not of land, or sky alone, but the channels, oceans and sea.
Seabirds hold a particular place in our affections. Bridging land and ocean like no other animal, they have become the subjects of poetry, books and film.
But their supposed abundance and place in our popular culture belies an underlying truth; that we still know very little about many of our sea-faring feathered friends.
Recent research is now helping to rectify that; revealing new insights into the lives of petrels, puffins and penguins, and how supposed land-loving birds are secret seabirds too.
Perhaps the biggest discovery though, is that seabird colonies have a previously unknown, global impact on the environment.A world of poo
British researchers have conducted the first global assessment of how much ammonia is produced by seabird colonies.
Birds on the box
The results, published in the journal Atmospheric Environment, are startling: seabirds excrete 404 Gigagrams (Gg) of ammonia each year.
That is 2% of all the ammonia produced in the world. Around 270 Gg is thought to enter the nitrogen cycle, with the rest being locked up due to cold temperatures.
Most of this ammonia is produced by a few key species; penguins account for 80% of all the ammonia produced globally by seabirds.
Macaroni penguins are prodigious excretors, accounting for a quarter of all seabird-produced ammonia, report researchers led by Stuart Riddick of the Centre for Ecology & Hydrology, Edinburgh, and King's College, London.
One colony of Macaroni penguins on Willis Island, South Georgia, excretes 15.6 Gg of ammonia per year, the highest rate ever estimated.
That makes penguin colonies the biggest biogenic source of ammonia on the planet, far exceeding that produced by poultry farms containing millions of birds.
Indeed, the only comparable natural source of ammonia was during the eruption of the Mount Mijake-jima volcano in Japan in 2000, which is thought to have released around 400 Gg of ammonia over the year.
The study, which combines data from 323 seabird species living in more than 30,000 colonies across 180 countries, also reveals there are far more seabirds alive today than thought.
In total, there are 1.18 billion seabirds in the world, compared to earlier estimates of 700 million. There are 261 million breeding pairs.Seabirds with talons
Last month, European scientists discovered that storm petrel seabirds can smell their relatives.
The study is the first evidence that birds are able to sniff out a suitable mate, and the researchers think this behaviour prevents the birds from "accidentally inbreeding".
Recently, scientists have also found that some bird species that were never considered seabirds in the first place actually depend on the marine environment for much of their food.
In 2009, scientists discovered that gyrfalcons living in the high Arctic overwinter out at sea, spending long periods living and hunting on pack ice.
Gyrfalcons are the world's largest falcon and it was the first time any falcon species has been found regularly living at sea.
The birds likely rest on the ice and hunt other seabirds such as gulls and guillemots, over what appears to be one of the largest winter ranges yet documented for any raptor.
Similar research published in 2011 in the Journal of Avian Biology showed that snowy owls are also secret seabirds.
Researchers fitted satellite trackers to 12 female snowy owls living on southern Bylot Island in Nunavut, Canada.
They discovered that the owls gather on sea ice around patches of open water, targeting other seabirds as prey, and that snowy owls rely on this marine source of food to survive the harsh Arctic winters.
Unable to fly
Evidence published earlier this year in Polar Research has also unveiled a previously unknown courtship behaviour by spectacled eider ducks.
Using a camera mounted on a helicopter, scientists zoomed in to film wintering flocks of eider containing tens of thousands of individuals.
The footage revealed that the ducks engage in "courtship scrums", where hundreds of birds, male and female, intermingle excitedly.
The scrums are so intense it seems unlikely that individuals can track one another to see how attractive they are; rather the scrums may serve to accelerate the hormonal development of the ducks, moving them from winter survival to breeding mode.Restoration projects
Our lack of knowledge is also reflected in the challenges that still face seabird conservation.
Nearly one in three seabird species are threatened with extinction due to various causes; including entanglement with fishing gear, pollution and the destruction of nesting sites by people or invasive species such as rats.
The UK-based Royal Society for the Protection of Birds has announced that kittiwake populations are declining at an alarming rate in Scotland.
Counts by RSPB Scotland and the Joint Nature Conservation Committee (JNCC) of Orkney's "seabird cities" reveal numbers of kittiwake breeding pairs have fallen 82% in just over a decade.
Populations on the Orkney mainland fell from nearly 11,000 pairs in 2000 to under 2,000 this year.
At Mull Head on the Orkney mainland, once bustling cliffs were empty this year as kittiwakes failed to return to the colony to breed, while experts fear a few colonies may go extinct within three years.
"The counts this year are deeply shocking, especially the loss of kittiwakes at Mull Head," says Doug Gilbert, RSPB Scotland Head of Reserves Ecology. He and his colleagues believe climate change is altering the marine environment in which the kittiwakes lives, triggering their decline.
Earlier this year, Holly Jones of the University of California and Stephen Kress of the National Audubon's Society's Seabird Restoration Project in Ithaca, New York published a review of the world's active seabird restoration projects, highlighting what we know and which techniques appear to work best to restore seabird populations.
Return of an elusive petrel
- In 2009, one of the world's rarest and most elusive birds was finally seen flying in its natural habitat.
- The Fiji petrel, a seabird that once "went missing" for 130 years, was sighted flying at sea, near the island of Gau in the Pacific Ocean.
- The culmination of a meticulously planned bird hunt, Birdlife International researchers sighted the birds 25 nautical miles south of Gau.
Their review, published in The Journal of Wildlife Management, identifies 128 active projects around the world trying to restore populations of 47 seabird species in 14 countries.
It includes some salutary lessons for the effort required to save seabirds.
For example, a pioneering seabird restoration project began in 1973 to return 954 Atlantic puffins to their historical nesting site on Eastern Egg Rock Island in Maine, US.
The project was the first to use decoy birds to attract the puffins back, but it still took four years for the first puffin to return, and eight years for the first egg to be laid on the island for more than a century.
Other more recent restoration projects rely on techniques such as translocating chicks from captivity or playing back sounds of nesting seabirds to entice new arrivals.
Pilot projects using such techniques and others have helped rescue Laysan albatrosses in Hawaii, Pycroft's petrels, Australasian gannets and Arctic and common terns.
"The opportunities for future research in seabird restoration is enormous," the researchers write.
But to save these sea-faring birds we need to know more about them, and their once secret habits.