http://news.bbc.co.uk/2/hi/science/nature/4874026.stm
Tuesday, 4 April 2006, 08:55 GMT 09:55 UK
Antarctic birds 'breeding later'
By Paul Rincon
BBC News science reporter
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.
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.
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."
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