The hunt is beginning to find a mysterious and rare seabird off the coast of Wales.
Conservationists will be searching two Pembrokeshireislands, Skokholm and Skomer, for the most enigmatic seabird in Wales - the European storm petrel.
They are related to the world's most famous ocean wanderers, the albatross, but weigh only about as much as a sparrow.
Despite their diminutive size, they range far out at sea for most of the year, braving the wildest of weather and spending winter off the coasts of South Africa.
As summer approaches, the Atlantic's tiniest seabird comes ashore to the breeding colonies among the rocks, boulders and scree slopes of these wild Welsh islands.
It is thought about 5,000 European storm petrels breed on Skokholm Island, representing up to 20% of Europe's breeding population, and a few hundred on Skomer, but no-one really knows because they are notoriously difficult to count.
Vicky Taylor, who is volunteering to count the bird, said: "We play the sound of a singing storm petrel to a likely nest site and if there's a bird in there it often calls back.
"It's supposed to sound like a fairy being sick but I think it's more like a purring cat with the hiccups."
The distinctive smell of storm petrels can also reveal a nest.
"It's a musty, oily smell, but distinctly pleasant," said Skomer assistant warden Jason Moss.
"If you get a strong whiff it can help to locate a nest burrow or a new breeding colony."
This year, conservationists will be attempting to complete a census of the "Quarry" on Skokholm Island, which is the largest breeding colony in England and Wales.
Warden Richard Brown says: "The Quarry is a natural amphitheatre of old red sandstone where hundreds of storm petrels nest in fragile crevices.
"Work there is challenging and requires careful planning, but what an office!"
The project is being carried out by the Wildlife Trust of South & West Wales and the University of Gloucestershire, with funding and support from Natural Resources Wales and forms part of the national seabird census.
The islands form the Skokholm and Skomer Special Protection Area and are world-famous for their seabirds, with internationally-important numbers of breeding Atlantic puffins and common guillemots delighting visitors by day, and half the world's population of Manx shearwaters coming out of their burrows by night.