Causes for earlier egg-laying not yet understoon
By Summit Voice
SUMMIT COUNTY — British scientists say they’ve measured a significant change in egg-laying dates for the wandering albatross – one of the largest birds on Earth. After studying the birds on the sub-Antarctic island of South Georgia, They have discovered that the laying date for the population is an average of 2.2 days earlier than 30 years ago.
At some nesting sites, wandering albatross populations have dropped by half in just a few decades, partly due to the impacts of expanding commercial fishing activities in the world’s southernmost oceans. Changing wind and weather patterns in some regions may also make foraging more challening.
“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,” said Dr, Sue Lewis, of the University of Edinburgh’s School of Biological Sciences. “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 more than 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.
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.
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 percent since the 1960s, from 1700 to only 800 breeding pairs.
“This work is important for understanding more about the behavior of these charismatic and threatened birds,” said British Antarctic Survey bird ecologist Dr. Richard Phillips, also an author on the paper. “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.”
Albatrosses cover huge distances when foraging for food, even during breeding, with the foraging ranges of most species covering thousands of square kilometers of ocean. Wandering albatrosses (Diomedea exulans) range from sub-tropical to Antarctic waters on trips covering up to 10,000 kilomters in 10to 20 days.
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.
Albatross deaths can be prevented by weighting fishing lines so they sink quickly, retaining of offal on board so that birds are not attracted to the vessel in the first place, setting lines at night, and deploying bird-scaring or ‘tori’ lines — made up of brightly-colored streamers to startle seabirds.
The wandering albatross is the largest of seabirds, with a wing span reaching 3m and a body mass of 8 to 12 kilos. It lays a single egg, and breeds only every second year — one of the lowest reproductive rates of any bird. The birds don’t reach sexual maturity until they’re 10 years old and live as long as 60 years. But many are now being killed off before they can reach half that age, as a result populations are in rapid decline.
The wandering albatross is site -faithful. 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.
This research is a collaboration between the University of Edinburgh and British Antarctic Survey and was funded by the Natural Environment Research Council.