Bill
Bourne
Watching
seabirds can be discouraging. Lots of seabirds can be seen from the
shore, but
they are mainly familiar inshore species milling around- any
strangers are
liable to be too far away or to pass too quickly for reliable
identification.
Trips in small boats are liable to be similar with the addition of
sea-sickness. During longer trips on larger boats little may be
seen out
at sea for much of the time except for terns calling at night in the
tropics,
until you go below to pack when approaching port, when you are
liable
to be told on returning that thousands of unrecognisable birds
appeared
over hundreds of cetaceans and tuna while you were below.
Nobody will
believe what you see anyway. In order to do better it is necessary to
consider
what is going on, and this is an attempt to describe some outstanding
past
investigations and summarise my own contributions.
The
sea
used to be regarded as a large quantity of undrinkable water mainly
notable for
unreliable weather. The distribution of birds over it begun to be
plotted in
the eighteenth and nineteenth centuries using guns, which was
then
necessary because they were still often new species, and nobody knew
what any of them looked like alive. One of the first
attempts to
identify this was made by Edward Wilson during his trips to the
Antarctic a
century ago, for which he had to prepare his own field guide, now in
the
Alexander Library at Oxford; unfortunately he did not return to publish
it.
Then in the 1920s W.B. Alexander himself prepared what Roger Peterson
recognised as the first proper field guide, The Birds
of the Ocean,
after trips to Australia and round the Southern Ocean, with guidance
from
Robert Cushman (Bob) Murphy who had made a trip to
South Georgia with
sealers (Murphy 1947).
One
of
the first attempts to work out what controls seabird distribution was
made by
Poul Jesperson (1930) during a Danish marine research expedition
in 1920-22. He found that the number of birds seen in ten
degree
rectangles in the North Atlantic varied with the density of the
plankton. Then
Vero Wynne-Edwards (1935) recorded the birds seen in five-degree
stretches
during eight voyages between the UK and Canada in 1933, and showed that
they
could be divided into inshore, offshore and pelagic communities, with
migrants
passing by at certain seasons. Neither of these paid much attention to
the bird
communities of the subtropical boundary currents, but meanwhile Bob
Murphy
(1936) was relating the information about the seabirds of South
America, and
especially the Humboldt Current, to the knowledge emerging about
oceanography
from the Discovery investigations
(it
is a pity there is still nothing comparable for the northern
hemisphere).
I
became
interested in the seabirds of the Canary Current during a student
expedition to
the Cape Verde Islands in 1951, which led to the study of the
world-wide sea
reports of the Royal Naval Bird-watching Society, and comparisons with
the
similar birds of the Arabian Sea (Bourne 1963). It became clear that
there was
a need for better organisation of British and Irish observations, which
led to
the formation of the first Seabird Group in 1966 (Bourne 1983a, 1989).
While
this was originally devoted to "sea-watching"- that is, watching
birds from the shore- it soon emerged following the wreck of the oil
tanker Torrey Canyon off Cornwall
in 1967
(Bourne et al.
1967), and
then a mass mortality of auks in the Irish Sea in 1969 (Bourne
1976a) that there was room for concern about both oil and
toxic chemical
pollution (Bourne 1976b). Funds were obtained for a national census of
breeding
seabirds named "Operation Seafarer" by the pioneer James Fisher, who
unfortunately did not live to complete it (Cramp et al. 1974), and then a study of birds
at sea around Scotland
(Bourne 1982a). Full development of the latter required the use of
computer
technology by the Natural Environment Research Council (Tasker et al. 1987, Webb et
al.1990).
The
conclusion from all this is that seabird distribution tends to be
controlled by
water movements, and especially mixing which brings the nutrients that
support
the growth of plankton at the bottom of the food chain to the surface.
In high
latitudes this is promoted by bad weather in the winter, which
is followed
by the growth of plankton in the spring. In the summer here and in
lower
latitudes the nutrients are soon exhausted and the water becomes
stratified
with a sterile surface layer. Mixing occurs in the oceanic boundary
currents,
reinforced by tidal movements along the shore, and where currents
diverge or
converge out at sea, notably where the Antarctic, Subantarctic and
Subtropical
water masses characteristic of the main belts of winds meet in the
southern
hemisphere and along the Equatorial Currents and
central Counter-current.
These
phenomena
are less marked in the closed oceans of the northern hemisphere, where
the
Corioli's force due to the rotation of the earth causes
currents to
deviate to the right, leading to a figure-of-eight circulation where
the water
moves clockwise around the oceans in the lower latitudes and
anticlockwise in
the higher ones, with upwelling in the intermediate area comparable to
the
southern subtropical convergence which seems to have received little
attention.
Where the prevailing wind drifts the surface water offshore there is
additional
upwelling along the boundary currents, reinforced by turbulence due to
the
tide, which incidentally combined with the SW prevailing wind may help
explain
the strong seabird communities off north-east Britain and Ireland.
All
this
results in the abundant birdlife offshore feeding largely on fish (and
not only
sand-eels: Bourne 1982a) which we all know about. In north-west
European waters
there is a wide continental shelf, so that until recently we have been
less
aware of events further out to sea, which are more obvious where the
shelf is
narrow, as on both coasts of the Americas. Here there tends to
be further
upwelling where deep currents hit the continental slope and
other
irregularities in the sea floor, such as submarine volcanoes or
"sea-mounts" (Bourne 1986, 1992b), and birds such as the
shearwaters, gadfly petrels tend to feed more on cephalopods,
and
possibly South Polar Skuas on the goose barnacles on
floating objects
(Bourne & Curtis 1994). There are no possible breeding-places
so far
offshore, so the birds feeding out there tend to breed to the south in
our
winter in the North Atlantic Islands and southern hemisphere, and are
only seen
exceptionally inshore.
The
situation is further complicated by variations in classification and
nomenclature. Basically the Victorians went on splitting species until
there
were an impossible number. Then in the last century people started
sticking
them together again as races and superspecies including some rather
distinct
entities in the process. I first encountered this with the observation
that the
variation of giant petrels included two fairly distinct entities that
bred at
different times and moved in different directions (Bourne &
Warham 1966).
Then it emerged that the same thing was happening in the north with
both the
"soft-plumaged" petrels (Bourne 1983b) and the "Manx"
shearwaters (Bourne et al. 1989).
The
main thing to remember about such things is that the birds
remain the same
whatever the fashionable variations in classification and nomenclature.
It
may be
asked what still needs to be done. Along the coast there is a need for
the more
methodical analysis of the vast accumulation of results of sea-watching
along
both sides of the British Isles (Wallace & Bourne
1981, Verrall &
Bourne 1982) in relation to the season and weather using computer
technology. Out at sea there is a need to get further out, a
couple of
hundred miles to the edge of the continental shelf, where
there are
sometimes a lot of interesting birds (Bourne 1986). The big
break-through
has come with observations from the UK-Spanish ferries which cross the
deep
water in the Bay of Biscay, where people appear to have become so
intoxicated
with the cetaceans that the birds have not been properly studied yet.
These
observations need to be made methodically, with timed counts
(I used to be
subject to interruptions, so made them for ten minute periods,
but tried
to accumulate at least a hour's worth two or three times a day) and
precise
positions- I have usually been able to use the bridge with charts
showing exact
positions and depths with the water temperature recorded
regularly, so that one knew where one was in relation to
shelfbreak fronts
and sea-mounts and upwelling, but it is now possible for anyone to
obtain a
satellite position indicator and find out at least their position for
themselves. There are a lot of birds out there somewhere, if you can
work out
the right places.
References
Bourne,
W.R.P. 1963. A review of oceanic studies of the biology of seabirds.
Proc. Int.
Orn. Congr. 13: 831-854. (Discusses the work of the Royal Naval
Bird-watching
Society, and among other things compares the seabird communities of the
subtropical areas of upwelling off West Africa and southern
Arabia).
Bourne,
W.R.P. 1972. Threats to seabirds. I.C.B.P.
Bull. 11: 200-218.
Bourne,
W.R.P. 1976a. The mass mortality of Common Murres in the Irish Sea in
1969. J. Wildl. Mgmt. 40: 789-792.
(Reviews a
lot of discussion. Originally attributed to pollution, it now seems
more likely
it was due to gales breaking up a front where the birds moult).
Bourne,
W.R.P. 1976b. Seabirds and pollution. Pp. 403-502 in Johnston, R. (Ed.)
Marine Pollution. Academic Press,
London.
Bourne,
W.R.P.
1980. The habitats, numbers and distribution of northern seabirds. Trans. Linn. Soc. New York 9: 1-14.*
Bourne,
W.R.P. 1981. Some factors underlying the distribution of seabirds. Pp.
119-134 in Cooper, J. (Ed.) Proc.
Symp. Birds of the Sea and Shore, 1979. African Seabird
Group, Cape Town.*
Bourne,
W.R.P. 1982a. The distribution of Scottish seabirds vulnerable to oil
pollution. Mar. Pollut. Bull. 13:
270-273. (Shows the relation to satellite views of, fronts, and that
their diet
is not entirely composed of sand-eels).*
Bourne,
W.R.P. 1982b. The manner in which wind drift leads
to seabird
movements along the east coast of Scotland. Ibis
124: 81-88.
Bourne,
W.R.P. 1983a. Seabird problems. Pp. 226-231 in Hickling, R. (Ed.) Enjoying Ornithology. Poyser, Calton.
Bourne
1983b. The Soft-plumaged Petrel, the Gon-gon and the Freira, Pterodroma mollis, P.
feae and P. madeira. Bull. Brit. Orn. Cl. 103: 52-58.
Bourne,
W.R.P. 1986. Late summer seabird distribution off the west coast of
Europe. Irish Birds 3: 175-198.
(Unfortunately a
satellite photo of the shelfbreak front SW of Britain did not reproduce
well).
Bourne,
W.R.P. 1989. Viewpoint- The Organization of Seabird Research. Mar. Pollut. Bull. 20: 158-163.
Bourne,
B. 1990. Bird movements about the North Sea. Pp. 71-82 in Alexander,
S.M.D.
(Ed.) Birds and the North Sea. 10th
Anniversary Publication of the North Sea Bird Club. North Sea Bird
Club,
Aberdeen. (Also covers radar observations of landbird migration).
Bourne,
W.R.P. 1992a. Debatable British and Irish seabirds. Birding
World 5: 382-390. (All the best unaccepted marine
hoodwinks).
Bourne,
W.R.P. 1992b. A concentration of Great Shearwaters and White-bellied
Storm-petrels over the RSA Seamount in the South Atlantic east of Gough
Island.
Sea Swallow 41: 51-53.
Bourne,
W.R.P. & Curtis, W.F. 1994. Bonxies, barnacles, and bleached
blondes. Brit. Birds 87: 289-298.
(Includes the
distribution of the South Polar Skua in the northern hemisphere).
Bourne,
W.R.P., Mackrill, E.J., Paterson, A.D. & Yesou, P. 1989. The
Yelkouan
Shearwater Puffinus (puffinus?) yelkouan.
Brit. Birds 81: 306-319.
Bourne,
W.R.P., Parrack, J.D. & Potts, G.R. 1967. Birds killed in the Torrey Canyon Disaster. Nature
215: 1123-1125. (Analysis of the
beached birds).
Bourne,
W.R.P. & Warham, J. 1966. Geographical variation in the giant
petrels of
the genus Macronectes. Ardea
54:45-67.
Cramp,
S., Bourne, W.R.P. & Saunders, D. 1974. The seabirds of Britain and Ireland.
Collins, London. (The first
complete census).
Jesperson,
P. 1930. Ornithological Observations in
the North Atlantic Ocean. Oceanogr, Rep. Danish 'Dana' Exp.
1920-1922. 7:
1-36. (First marine census).
Murphy,
R.C. 1947. Logbook for Grace: whaling
brig Daisy 1912-1913. MacMillan, New York. (How it used to
be).
Murphy,
R.C. 1936. The Oceanic Birds of South
America. 2 vols., American Museum of Natural History, New
York. (The most
monumental pioneer study).
Tasker,
M.L., Webb, A., Hall, A.J., Pienkowski, M.W. & Langslow, D.R.
1987. Seabirds in the North Sea.
Nature
Conservancy Council, Aberdeen.
Verrall,
K. & Bourne, W.R.P. 1982. Seabird movements around western
Islay. Scott. Birds 12: 3-10. (What
happens on
the west coast).
Wallace,
D.I.M. & Bourne, W.R.P. 1981. Seabird movements along the east
coast of
England. Brit. Birds 74: 417-426.
(What happens on the east coast- the title should have referred to
Britain).
Webb,
A.,
Harrison, N.M., Leaper, G.M., Steele, R.D., Tasker, M.L. &
Pienkowski, M.W.
1990. Seabird distribution west of
Britain. Nature Conservancy Council, Aberdeen.
Wynne-Edwards,
V.C. 1935. On the habits and distribution of birds on the North
Atlantic. Proc. Boston Soc. Nat. Hist.
40:
233-346. (Pioneer transects).
(I
still
have reprints of the obscure publications with asterisks).
W.R.P. Bourne