Antarctic birds 'breeding later'

[Guest guest]

By Paul Rincon

BBC News science reporter

 

 

Birds such as this Cape petrel have been arriving and breeding later

Antarctic seabirds may be breeding later in response to climate

change, according to a scientific study.

French researchers analysed records stretching back to the 1950s and

think the breeding delays are linked to changes in East Antarctic sea

ice.

Bird species are arriving at their colonies an average of nine days

later and laying eggs on average two days later than they did in the

1950s.

Details appear in Proceedings of the National Academy of Sciences

journal.

Researchers have found that spring events such as the arrival of

migrant birds and the blossoming of trees, have been occurring

progressively earlier in the Northern Hemisphere during the 20th

Century.

But little information exists for the Southern Hemisphere due to a

paucity of long term data sets.

Late arrivals

Christophe Barbraud and Henri Weimerskirch from the Centre d'Etudes

Biologiques de Chize in Villiers en Bois, France, have now analysed

the only long term record of arrival and egg-laying for all species

of seabird that come to breed in continental Antarctica.

 

Changes in sea ice may be behind the breeding delays

Data on the nine species of bird were collected by ornithologists at

the Dumont d'Urville Antarctic research station between 1950 and

2004.

Over this period, four species showed a clear trend towards arriving

later in Antarctica and two showed a clear trend toward later

breeding.

Most other species arrived and bred later, but the trends were not

statistically significant at levels set by the French team.

This is the opposite pattern to that seen in the Northern Hemisphere.

It is likely that progressively warmer Northern Hemisphere spring

temperatures since the mid-20th Century have increased the

availability of food supplies.

In eastern and continental Antarctica, no warming or cooling has been

observed since the early 1950s.

Breeding success

Here, a 12-20% reduction in the extent of sea ice over the last 50

years has been linked to a decline in numbers of the krill and other

marine organisms that are the major food source for seabirds.

In addition, the sea ice season has been getting longer since the

1970s. The late break-up of sea ice is known to delay access to

seabird colonies and food resources at sea.

 

There are few long-term data sets for Antarctic fauna

These two factors reduce the quantity and accessibility of food

supplies available in early spring, with birds requiring more time to

build up the reserves they need to breed.

" We think both these factors contribute to the delays observed but do

not explain all of the delays observed, " Dr Barbraud told the BBC

News website.

The changes in sea ice explain only 24% of the variation in arrival

and egg-laying, so other factors must be at work. Dr Barbraud said

these would need to be identified before predicting how the observed

trends would affect breeding success.

But if seabirds continue to arrive and breed later and later, it

looks likely that juveniles will fledge - gain the ability to fly -

just before winter.

" They would face very harsh conditions just after fledging, " Dr

Barbraud explained, " They would have less time to learn how to find

resources on their own. "

Paul.Rincon-INTERNET