Hi folks,

Kelly et al.'s discussion on pigeons' milk sent me back to my old copy
of Carl Welty's "The Life of Birds" (2nd Edition, WB Saunders Co) to
see what I've (once again) forgotten from my old ornithology courses...

In the chapter on reproduction, the discussion on reproductive
hormones tells us:

"The pattern of growth and maturation of the ovarian follicles is
regulated by the follicle-stimulating hormone of the anterior pituitary
gland or adenoohypophysis. In males the pituitary provides a similar
hormone which sitmulates testis growth. A second pituitary secretion,
the luteinizing hormone, stimulates the growth and activity of the
interstitial cells in both the ovary and testes, and controls the discharge
of the ovum from its follicle. Later in the reproductive cycle, the
pituitary gland liberates a third hormone, prolactin, which depresses
the production of both the follicle-stimulating and luteinizing hormones,
and initiates broodiness (nesting and incubation) in a bird. Prolactin
also causes milk secretion in mammals and crop secretion ("pigeon's
milk") in pigeons and doves."....

Later, in the section on "Care and Development of the Young", Welty
discusses regurgitation of food to the nestling, then goes on to say:

"All pigeons and doves regurgitate "pigeon's milk," a creamy substance
with a make-up very similar to rabbit's milk. Typical pigeon's milk
contains about 72 per cent water, 15 per cent protein, 10 per cent fat
1.5 per cent ash, 1.5 per cent other nitrogen compounds, and no
carbohydrates. It is rich in calcium and in vitamins A, B, and B1. Even
more remarkably, as Lewis (1944) has revealed, the same endocrine
mechanisms are involved in each animal. The milk of pigeons and
mammals comes from fatty cells shed from the epithelial tissues in
either the bird's crop or the mammal's mammary glands. If prolactin
from the anterior pituitary gland is injected experimentally into these
animals, both crop and mammary glands will begin producing milk.
Not only will the crop walls of the pigeon begin functioning, but the
pigeon will exhibit broodiness and protective care of eggs and young.
As little as 0.1 microgram of prolactin injected subcutaneously will
cause the crop of a pigeon to begin manufacturing milk. Young
domestic pigeons feed on pigeon's milk some 5 days; then, for up to
18 days, they eat a mixture of pigeon's milk and crop-softened grain."

"Oily fluids from the digestive tract are used by other species to feed
their newly hatched young...."

Although most of my reference books note the general "fondness" of
pigeons and doves for salt, and mention attendance at mineral springs
or beaches, I do not have any reference on the contribution of the
minerals or mineral springs to the bird's production of the pigeon's milk.
Is the salt/mineral an aid to - or is it a requirement for - the physiological
production of the milk?

Interesting discussion.

Jon. Anderson
Olympia, Washington
festuca at olywa.net