A new study of the wandering albatross - one of the largest birds on Earth - has shown that some of the birds are breeding earlier in the season compared with 30 years ago.

Reporting online this month (April) in the journal Oikos, a British team of scientists describe how they studied the breeding habits of the wandering albatross on the sub-Antarctic island of South Georgia. They have discovered that because some birds are now laying their eggs earlier, the laying date for the population is an average of 2.2 days earlier than before.

The researchers say the reasons for this change are unclear. Lead author Dr Sue Lewis at the University of Edinburgh's School of Biological Sciences said, "Our results are surprising.

Every year we can determine when the birds return to the island after migration, and the exact day they lay their egg. We knew that some birds were laying earlier - those who were older or had recently changed partner - but now we see that those which haven't bred successfully in the past are also laying earlier, and these birds are effectively driving this trend in earlier laying".

The researchers studied over 30 years of data from birds located near the British Antarctic Survey's research station on Bird Island (part of South Georgia). Nest sites were monitored daily during the pre-laying, laying, hatching and fledging periods to document breeding patterns.

Numbers of wandering albatrosses on South Georgia have been steadily declining largely because the birds swallow baited hooks on longlines set by fishing vessels, and are dragged under and drown.

Despite a recent increase in breeding success over the last 20 years, the number of birds at Bird Island has fallen by over 50% since the 1960s, from 1700 to only 800 breeding pairs.

British Antarctic Survey bird ecologist Dr Richard Phillips, also an author on the paper said, "This work is important for understanding more about the behaviour of these charismatic and threatened birds. In the Indian Ocean, an increase in the intensity of westerly winds has resulted in a shift in feeding distribution of wandering albatrosses. It is possible that earlier breeding in some females at South Georgia is a consequence of environmental change, but at the moment we are not sure if this is related to weather, a change in oceanographic conditions or food availability to which only some birds are responding."

This research is a collaboration between the University of Edinburgh and British Antarctic Survey and was funded by the Natural Environment Research Council (NERC).

Intrinsic determinants of a population trend in timing of breeding in the wandering albatross by Sue Lewis, Daniel H. Nussey, Andrew G. Wood, John P. Croxall and Richard Phillips is published online this month (April) in the journal Oikos.

Stunning broadcast-quality footage and stills of South Georgia, Antarctica and wandering albatross colonies are available from the BAS Press Office as above.

The wandering albatross is the largest of seabirds, with a wing span reaching 3m and a body mass of 8-12 kg. It lays a single egg, and breeds only every second year. The birds take ten years to reach sexual maturity.

They have very long life spans, with some individuals living to over 60 years of age. But many are now being killed off before they can reach half that age, as a result populations are in rapid decline. Albatrosses have one of the lowest reproductive rates of any bird.

Albatrosses cover huge distances when foraging for food, even during breeding, with the foraging ranges of most species covering thousands of square kilometres of ocean. Wandering albatrosses (Diomedea exulans) range from sub-tropical to Antarctic waters on trips covering up to 10,000 km in 10-20 days.

The wandering albatross arrives in November to breed in loose colonies on flat grasslands, giving plenty of room for its spectacular displays. It lays eggs in December, chicks hatch in April and are reared throughout the winter (on a diet mainly of squid and fish) fledging after more than a year, in November and December. Successful parents then take a year off, migrating to feeding areas all around the Southern Ocean.

The wandering albatross is site faithful and breeds every two years. Without BAS's individual based study on Bird Island, the differences between good and poor breeders would be lost. Knowing that such individual variation exists is crucially important if scientists want to understand population processes correctly, highlighting the incredible value of long term individual based studies such as this one.

Estimates suggest that 300,000 seabirds are killed annually in the world's longline fisheries. Since 2001, by-catch rates in well-regulated fisheries have decreased substantially, remained stable in less well-regulated ones and probably increased in pirate fisheries.

Several albatross species - legendary protectors of seafarers - are heading for extinction. Biologists have discovered that swordfish, tuna and other fishing fleets are killing more than 100,000 of these birds every year.

In a couple of decades some may be wiped out unless urgent action is taken. This is despite the availability of a range of measures that can massively reduce the number of albatrosses being killed.

These include weighting of lines so they sink quickly, retention of offal on board so that birds are not attracted to the vessel in the first place, setting lines at night, and setting up bird-scaring or 'tori' lines - made up of brightly-coloured streamers to startle seabirds.