P
peter hayes
Guest
This is what the BBC have to say about seabirds:
Most seabirds can easily tolerate weather conditions which man finds
appalling. To survive life in the open they have to be capable of
withstanding gales, low temperatures, considerable wind chill and the
full measure of precipitation from which there is no escape. In response
to the needs of finding food they migrate vast distances and while some
species have fixed breeding and wintering areas others are highly
nomadic and are opportunistic breeders.
Of all the forces of nature, wind has the greatest influence on the
lives of seabirds. On the one hand it is an element to be battled
against, on the other it is the means by which travel is assisted and
globetrotting journeys are made possible. Shearwaters perform
semi-continuous migrations and roam the oceans in both hemispheres of
the Earth. To do this they synchronise flying skills with detailed
knowledge of the world's wind circulation.
Flight in calm conditions is labour intensive so, even if birds are in
transit over barren feeding grounds, they prefer to save energy and sit
on the sea to await favourable winds. Conversely, strong headwinds sap
energy and less powerful fliers opt to settle rather than persevere in
the face of adversity. Hence, for all species the wind has both an
optimum strength and direction. Computing these two variables is the key
to high-mileage, energy-efficient travel.
Seabirds are genetically programmed to detect shifts in barometric
pressure and, especially during autumn in the northern hemisphere, they
move south in the wake of eastward-moving depressions. Weather fronts
laden with cloud and rain are associated with low pressure. Behind them
pressure rises and visible signs of improvement are clearing skies and a
brisk, cool breeze.
Seabirds grasp the ideal flying conditions by instinct, but we have to
pay close attention to weather charts if we wish to spot the window of
opportunity that they exploit. Many birdwatchers have an ulterior motive
for keeping an eye on the weather. They want to see the birds themselves
and because mass movements coincide with blustery west or north-west
winds it is possible to see many individuals in the course of just a few
hours. Predict the timing of wind veering into the desired quadrant and
a glittering array of species can be seen. However, if the wind dies or
fails to shift direction (or if meteorologists got the forecast wrong)
then the parade of seabirds will not form.
The scale of numbers is one exciting ingredient in what passes, the
presence of birds from far afield is another. Species that forage over
inaccessible oceanic waters during the northern hemisphere's summer, or
nest in polar regions but spend the winter in the southern oceans, are
on their way south in autumn. As recently as 30 years ago no one
imagined that it was possible to see such sights comparatively close to
home.
The trick is being in the right place at the right time. And, for once,
it is possible to use a cliché with conviction: identifying the range of
types is an exact science. However, never mind the subtle differences
between species, nothing compares to the spectacle of lines of seabirds
rising and falling against the backdrop of a stormy sea.
Recognising unusual or seldom seen birds gives an added sense of
wonder. Leach's storm petrels inhabit deep offshore waters and nest on
remote, tiny islands where they come and go under the cover of darkness.
During winter they shift southwards and vanish over tropical seas. Yet,
come September, they can be deflected along windward coasts of the
British Isles by north-west winds. Pursuing them may be pomarine skuas
from the tundra of arctic Russia; another species en route to the
southern hemisphere but present off western Europe at the same time.
Any bird whose name is prefaced by that of the person credited with
discovering it usually denotes an absorbing piece of history. Sabine's
gull was found by Edward Sabine i
n 1818 while searching for the
north-west passage along the west coast of Greenland. He shot several
individuals of a delicate, tern-like gull that he found accompanying
flocks of Arctic terns. The specimens were exhibited in London and the
bird was named in his honour. Nothing more was heard of the species
until another was found four years later. This time the location was not
so distant but nonetheless amazing for a bird so new to science: one was
killed on Belfast Lough on 18 September 1822.
Today we know that this beautiful small gull breeds in several regions
of the high Arctic and winters locally over cold currents off South
Africa and South America. This much became clear in the middle of the
twentieth century. It took longer to understand its true status west of
Europe. The fact that we now realise that many hundreds accumulate in
the Bay of Biscay during autumn is not news to the birds. Moreover,
should a vigorous Atlantic depression sweep over the United Kingdom in
mid-September, the winds in its tail will probably speed Sabine's gulls
southwards through our inshore waters. And, to prove it, they still
appear on Belfast Lough - no prize for guessing the peak date!
Most seabirds can easily tolerate weather conditions which man finds
appalling. To survive life in the open they have to be capable of
withstanding gales, low temperatures, considerable wind chill and the
full measure of precipitation from which there is no escape. In response
to the needs of finding food they migrate vast distances and while some
species have fixed breeding and wintering areas others are highly
nomadic and are opportunistic breeders.
Of all the forces of nature, wind has the greatest influence on the
lives of seabirds. On the one hand it is an element to be battled
against, on the other it is the means by which travel is assisted and
globetrotting journeys are made possible. Shearwaters perform
semi-continuous migrations and roam the oceans in both hemispheres of
the Earth. To do this they synchronise flying skills with detailed
knowledge of the world's wind circulation.
Flight in calm conditions is labour intensive so, even if birds are in
transit over barren feeding grounds, they prefer to save energy and sit
on the sea to await favourable winds. Conversely, strong headwinds sap
energy and less powerful fliers opt to settle rather than persevere in
the face of adversity. Hence, for all species the wind has both an
optimum strength and direction. Computing these two variables is the key
to high-mileage, energy-efficient travel.
Seabirds are genetically programmed to detect shifts in barometric
pressure and, especially during autumn in the northern hemisphere, they
move south in the wake of eastward-moving depressions. Weather fronts
laden with cloud and rain are associated with low pressure. Behind them
pressure rises and visible signs of improvement are clearing skies and a
brisk, cool breeze.
Seabirds grasp the ideal flying conditions by instinct, but we have to
pay close attention to weather charts if we wish to spot the window of
opportunity that they exploit. Many birdwatchers have an ulterior motive
for keeping an eye on the weather. They want to see the birds themselves
and because mass movements coincide with blustery west or north-west
winds it is possible to see many individuals in the course of just a few
hours. Predict the timing of wind veering into the desired quadrant and
a glittering array of species can be seen. However, if the wind dies or
fails to shift direction (or if meteorologists got the forecast wrong)
then the parade of seabirds will not form.
The scale of numbers is one exciting ingredient in what passes, the
presence of birds from far afield is another. Species that forage over
inaccessible oceanic waters during the northern hemisphere's summer, or
nest in polar regions but spend the winter in the southern oceans, are
on their way south in autumn. As recently as 30 years ago no one
imagined that it was possible to see such sights comparatively close to
home.
The trick is being in the right place at the right time. And, for once,
it is possible to use a cliché with conviction: identifying the range of
types is an exact science. However, never mind the subtle differences
between species, nothing compares to the spectacle of lines of seabirds
rising and falling against the backdrop of a stormy sea.
Recognising unusual or seldom seen birds gives an added sense of
wonder. Leach's storm petrels inhabit deep offshore waters and nest on
remote, tiny islands where they come and go under the cover of darkness.
During winter they shift southwards and vanish over tropical seas. Yet,
come September, they can be deflected along windward coasts of the
British Isles by north-west winds. Pursuing them may be pomarine skuas
from the tundra of arctic Russia; another species en route to the
southern hemisphere but present off western Europe at the same time.
Any bird whose name is prefaced by that of the person credited with
discovering it usually denotes an absorbing piece of history. Sabine's
gull was found by Edward Sabine i
n 1818 while searching for the
north-west passage along the west coast of Greenland. He shot several
individuals of a delicate, tern-like gull that he found accompanying
flocks of Arctic terns. The specimens were exhibited in London and the
bird was named in his honour. Nothing more was heard of the species
until another was found four years later. This time the location was not
so distant but nonetheless amazing for a bird so new to science: one was
killed on Belfast Lough on 18 September 1822.
Today we know that this beautiful small gull breeds in several regions
of the high Arctic and winters locally over cold currents off South
Africa and South America. This much became clear in the middle of the
twentieth century. It took longer to understand its true status west of
Europe. The fact that we now realise that many hundreds accumulate in
the Bay of Biscay during autumn is not news to the birds. Moreover,
should a vigorous Atlantic depression sweep over the United Kingdom in
mid-September, the winds in its tail will probably speed Sabine's gulls
southwards through our inshore waters. And, to prove it, they still
appear on Belfast Lough - no prize for guessing the peak date!
