Re: feathers as parasite protection?

[Dino Guy and a Lady <gigi.babcock@alumni.usc.edu>]

Sorry to nitpick, but...

Regarding birds and parasites, _Life Nature Library: Ecology_ states:

"'Birds,' wrote the scientist A. E. Shipley, 'are not only birds but aviating
zoological gardens.'  The range of tiny creatures that birds carry aloft with
them is truly impressive: their feathers are eaten by lice and mites, their
skin by certain flies; fleas, lice, mosquitoes, leeches, ticks and others suck
their blood from the outside while protozoa destroy their red blood corpuscles
from the inside; varieties of parasitic worms are located in practically every
organ of a bird's body.  From the time that it is born in its snug nest, which
is also favorable habitat for intruders, the hatchling encounters the grim
realities of parasitism.  One study of the nests of 56 species of birds
revealed the presence of no less than 529 species of arthropods -- most of them
mites and beetles.  Throughout its life, the bird is attacked by
representatives of nearly every group of parasitic animals, ranging from
one-celled microorganisms up the evolutionary ladder to birds themselves --
such as the European cuckoo, American cowbird and African honey guide -- which
induce other birds to feed and rear their broods for them.  Not only do a wide
variety of parasites attack birds, but also the numbers of any single parasitic
species are often extremely high: more than 1,000 feather lice, for example,
were taken from the plumage of a single curlew."

Later, the book goes on:

"By dust bathing and preening, the host holds down their numbers on the
feathers and skin, and special blood cells and antibodies fight to prevent
overcrowding in the lungs, liver, trachea and blood.  If this balance is upset,
the parasites take over, bringing disease and often death to the host."

It seems to me that furry or feathery integuments provide an irresistible
habitat for external parasites, providing ample surfaces which are easy to
cling to, easy to attach eggs to, and easy to hide within.  I would think that
it would be far easier for an animal to locate and remove lice and nits from a
relatively hairless or featherless region of the body than one which is thick
with hair or feathers.  As for the utility of shedding infested filaments to
facilitate the eradication of parasites, it seems to me that this method would
be ineffectual, given the slow rate of shedding and the rapid life cycles of
parasites.  Besides, some parasites, such as fleas, ticks, and mosquitoes,
spend much of their time not on the host, but rather in the general vicinity,
such as the nest.

 _Nature_ magazine reported on the discovery of a 120 million year old feather
from the Crato Formation of northeast Brazil with 100 small structures believed
to be feather mite eggs attached, in the article, "Did dinosaurs come up to
scratch?," (Martill, David M., and Davis, Paul G., _Nature_ Volume 396, 10
December 1998, pp. 528-529).  A brief commentary on page 26 of the March 1999
issue of _Scientific American_, entitled "Feathers, Flight and Faith" refers to
this paper, saying: "So it would seem that feathers, a supreme evolutionary
achievement, were fouled from nearly the start."

So, yes, I would think that feathers do serve as excellent parasite protection
-- they protect parasites very well!

On the other hand, as Ken Kinman suggests, many animals successfully groom
themselves to minimize parasite populations (also see earlier posts on
"anting"), and a good looking set of feathers is believed to assure females
that a male bird is relatively free of parasites and therefore may make for a
suitable mate.  The pressure to prove one's relative absence of external
parasites is believed to have been among the forces which led to the beautiful
display feathers we see in birds today.  They act as a billboard to broadcast
to the female birds: "I'm clean, baby.  Come and get it!"

Mutual grooming is often an essential aspect of bonding behavior and would
certainly qualify as a useful behavioral adaptation.  C'mon, documentarians,
let's see a tender grooming moment between a pair of feathered non-avian
maniraptorans.

-- Ralph W. Miller III   ralph.miller@alumni.usc.edu

"'Tis better to groom the goose than to goose the groom."