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By:
Paul Rincon
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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BBC
News -
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