The deaths of up to 20,000 seabirds off the Dutch coast has left puzzled authorities searching for clues.
Hundreds of emaciated guillemot carcasses began appearing along the Wadden Island coast last month, wildlife conservation group Ecomare said, while thousands more are believed to be dead at sea.
The species is renowned for spending its life on the ocean, and only returns to land to nest.
"If a guillemot is on the beach, something is going on," Ecomare said in a statement, adding that a number of sickly birds had been taken into its care for treatment.
Researcher Mardik Leopold, who is investigating the deaths, told The Guardian he had not seen "such mass deaths since the 1980s and 1990s".
"The working hypothesis is that it is a combination of bad weather plus something else, and we are trying to find the smoking gun," he said.
"We have dissected some of the birds. They are clean but they were very skinny with gut problems which is indicative of starvation."
The deaths have prompted concerns the birds may have fallen victim to a container spill from the MSC Zoe, which lost hundreds of containers — including children's toys, furniture and televisions —when it encountered heavy seas off the Netherlands last month.
Mr Leopold said although the containers would "inevitably" contain plastic and chemicals, his colleagues in nearby Germany and Belgium had not encountered similar bird deaths.
"A dead bird is found on every kilometre of beach along the Dutch coast every day, and the rate is steady, it isn't dropping off," he said.
