SOME OF THE REASONS I KEEP BIRDS
are that I love watching their behaviours,
learning about how better to provide
for their needs and, ultimately, being
successful in supporting them to have
more successful breeding seasons. I think
this is a common thread throughout the
avicultural community, supported by the
outstanding positive innovations to emerge
in the hobby over the past 20 years. We
have far surpassed ‘the dark ages’ in which
birds were thrown into an aviary and left
to their own devices to either survive and
perhaps breed, or die and be replaced.
But could there be intricacies of weather
patterns and environmental variables that
are just beyond our control? This question
may have a hint of climate change, but do
not jump to conclusions. I am thinking
about shorter-term climate cycles of
perhaps less than 10 years that infl uence
rainfall or temperature and, ultimately,
the health and survival of our birds. These
are patterns that have been running for
thousands of years yet are still something
of a puzzle.
SOUTHERN OSCILLATION INDEX
Anyone that watches the nightly weather
reports will hear mention of the Southern
Oscillation Index and perhaps see graphs
as the data dips and rises throughout the
year. If you are like myself, you may have
a general idea of what this entails but, not
being a meteorologist, a true understanding
is sadly lacking. This phenomenon of the
El Nino Southern Oscillation (ENSO)
has a great infl uence on the climates of
land masses bordering the Pacifi c Ocean,
causing irregular but periodic variation in
wind and sea surface temperatures.
There are three phases—the warming
phase is referred to as El Nino, the cooling
phase is La Nina and there is a neutral
phase. The cooling and warming phases
typically last a few months but may not
occur every year, instead being replaced by
the more frequent neutral phase. Several
components are interacting with each
other that eventually cause changes in
ocean surface temperatures and a gradient
of colder water in the eastern Pacifi c
(Peru and Chile) and warmer water in the
western Pacifi c (Australia).THE WALKER CIRCULATION
The pattern of differing atmospheric
conditions where a low pressure system
dominates the area around Indonesia and a
high pressure system occurs in the eastern
Pacifi c is called the Walker Circulation.
During La Nina conditions, this circulation
causes easterly equatorial winds to push
eastern very cold surface waters towards
the west. The result is that waters become
warmer and are associated with a moister
atmosphere, delivering increased rainfall
to eastern Australia. This is referred to as
the cold phase—even though water is being
warmed along the equator—because, as a
result of the Walker Circulation, the water
at the beginning of this phase is colder
because of the depth from which the water
originates along the coast of Peru.
During periods when the Walker
Circulation declines in intensity, a warming
phase or El Nino commences. A lack of
circulation results in reduced upwelling
of deep cold ocean water and, therefore,
the waters eventually fi nding their way to
eastern Australia (western Pacifi c) have
already started at a signifi cantly higher
temperature and an associated drier
atmosphere. The result is less rainfall inThis New Holland Honeyeater is one of
the many species of woodland bird
adapting nesting attempts to the Southern
Oscillation IndexCoastal woodlands in southern Australia hold a wealth of bird species which are
disappearing with the pressure of land clearing for urban expansionAustralia. El Nino episodes are seen as
negative fi gures in the Southern Oscillation
Index (SOI) and La Nina have positive
SOI fi gures. The sea surface temperatures
during La Nina are about 3–5oC below
normal, whereas in an El Nino event, the
temperatures are the reverse.
We know very well that the El Nino
Southern Oscillation (ENSO) strongly
infl uences rainfall and, as Australians,
we are all too aware of the prevalence of
droughts when El Nino is at its peak.EL NINO AND BREEDING
Precipitation is correlated with the
breeding success of numerous bird
species. Under poor rainfall conditions,
birds in Australia tend to either reduce
their breeding efforts or not breed at all
and wait until higher rainfall in following
seasons. However, it was not until very
recently that academics investigated theLooking to the Skies
THE WISE OWL
AUTHOR AND IMAGES DR MILTON LEWIS BSc (Hons) PhD