Here is another installment of readings on the cormorants. Its getting a
little bit more difficult to gather and read articles now that I'm working.
But no excuses! I still have three longer articles to digest and report on.
My thanks to Anna Coles for directing me to the Journal of Experimental
Biology. My research techniques are rusty.

Cormorants

Cambridge Encyclopedia of Ornithology
Pg. 138 Feather Care and Moult

Although the oils produced by the preen gland are formed from a mixture of
fatty substances, there is considerable intraspecific variation, and even
individual variation as to the precise nature of the oils. The size of the
preen gland and the nature of the oils produced may also vary with season.
For example, in waterfowl, the makeup of the preening oil is different at the
time of the eclipse (basic) plumage than it is for the breeding )alternate)
plumage. These changes are apparently brought about the by the direct
influence of specific hormones to which the gland is sensitive.
Preening oil assists waterproofing in birds. This may result from its own
oily properties or its ability to help preserve the physical structure and
flexibility of the feathers. Its effectiveness as a water repellent, however,
shows interspecific variation. For example, although cormorants and anhingas
possess preen glands, their flight feathers become waterlogged during diving.
As a result, they frequently spread their wings and tails to dry after
periods of diving. During preening, oils are applied to the naked parts of
the body including bills and feet. Thus, oils may be essential to maintaining
the condition of exposed parts of the skin. Preening oils may even possess
antibiotic substances that could help to control bacterial and fungal
infections. Finally, it has been suggested that components of the oils, when
exposed to sunlight, become converted to vitamin D. The vitamin could then be
absorbed through the skin or ingested during preening. 


Dictionary of Birds, Campbell and Lack eds. Buteo Books 1985
Cormorants pg. 110
... Modified barbs on the contour feathers allow air to escape and water to
penetrate the body plumage, thus reducing buoyancy. Ingested pebbles also
reduce buoyancy, and may serve to adjust the centre of gravity. Cormorants
swim low in the water. Ashore the water is shaken and aired out of the
plumage. Secretions from the oil gland help the plumage shed rain and spray.
Most species spread their wings to dry, but not sub-Antarctic forms of
Leucocarbo. In addition to drying, the spreading of wings may have several
other functions, including thermoregulation and grooming. 


Living Birds of the World, Thomas Gilliard, Doubleday, 1958
Cormorants
..Unlike many swimming and diving birds, cormorants presumably cannot remain
long in water or sleep afloat because their plumage is not water-repellent
and soon becomes sodden. Even after short submersions they must therefore dry
their plumage, and often sit in the sun with wings outspread.



Handbook of the Birds of the World, Volume 1 1992
Cormorants pg. 331
The Wing-spread position is very characteristic of these birds, and is a
posture they often maintain for long periods. The significance of the posture
has been interpreted in various different ways: for thermoregulation; for
drying the wings; to help the bird keep their balance in an upright stance;
or for producing intraspecific signals, such as the announcement of
successful fishing. However, studies of several species indicate that its
only purpose seems to be for drying the wings. Hence the thermoregulatory
function in the Wingspreading of the darters is lacking in cormorants,
although the ultimate aim in cormorants might be to conserve energy.


The Water Repellency and Feather Structure of Cormorants, Phalacrocoracidae,
A. M. Rijke
Journal of Experimental Biology, 48, 185-189
Summary
1. The water-repellency of the feathers of ducks is greatly increased by a
structural feature which can be expressed in terms of diameter and spacing of
the barbs and barbules.
2. This structural parameter is smaller for cormorants feathers and causes a
lesser extent of water repellency.
3. The resulting wetness of the feathers is the proximate cause of the
cormorants characteristic habit of wing-spreading.


thats all for now. more later


Jim Rosso
Issaquah
206-392-8440