For a tern in the northern hemisphere, life may be about to take a turn for the worse. For murres or guillemots, as the temperature rises, the chance of survival takes a dive. Many of the world’s seabirds could be in trouble.

And for a mix of reasons, the birds of the southern hemisphere could also be heading into difficulties, but at a slower pace. A worldwide team of 40 ornithologists has looked at 50 years of breeding records for 67 seabird species to find that as global temperatures notch up, breeding rates are down. That may be just an indicator of deteriorating conditions on and below the surface of the oceans: the researchers call their seabird subjects “ecosystem sentinels”.

The scientists report in the journal Science that they used their data to test a proposition: that seabird productivity − the numbers that survive each breeding season − would track “hemispheric asymmetry” in ocean climate change and human use.

Put simply, because there is less land and fewer people south of the Equator, because the southern waters are less overfished and subjected to lower pollution levels, and because a bigger ocean space ought to absorb extremes of heat more effectively, seabird survival rates would be worse north of the line than to the south.

And that is because the fish and plankton that seabirds eat can move with the climate, but the seabirds cannot: during the breeding season, they return to the same colonies.

“Seabirds travel long distances — some going from one hemisphere to the other — chasing their food in the ocean. This makes them sensitive to changes in things like ocean productivity, often over a large area,” said P. Dee Boersma, a conservation biologist at the University of Washington in the US.

“They have to compete with us for food. They get caught in our fishing nets. They eat our plastic, which they think is food. All of these factors can kill off large numbers of long-lived seabirds.”

Read the full article about seabird warnings on ocean conservation by Tim Radford at Eco-Business.