STUDIES ON THE PHYSIOLOGY OF REPRODUCTION IN BIRDS

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Abstract
Adult breeding pairs of birds (28 common pigeons, 30 ring doves) in individual full-size cages, were permitted to complete one or more reproductive cycles under measurement involving daily weighings of food consumed, and the weighing of the 2 parent birds at 2 or 3 day intervals for 6-7 wks.; crop-contents, when present, were carefully estimated and deducted from the total wt. of the birds. The body wt. undergoes a cyclic increase of ca. 8% during the 15 or 18 days spent in incubation of the eggs. Max. wt. is attained at the end of incubation. Nearly 1/2 of this increase occurs in the crop-glands under the specific stimulus of prolactin. The remainder of the increased wt. seems to occur in the body in general (except skeleton) ; it is now indistinguishable from true body growth, and is believed to have a hormonal basis which in time relations at least is associated with the release of prolactin. A cyclic decrease in body wt. begins as soon as parent birds begin to feed their young and continues for approximately 15 days. Probable causes of this loss of wt. are considered. The amt. of food consumed during the several stages of the reproductive cycle was measured. For more than 1/2 of these birds the cyclic period of growth was a period of subnormal consumption of food[long dash]23 gm. daily for a pigeon in the "resting" stage and 20 gm. while incubating eggs. At 10-12 days after hatching the young pigeon daily consumes a quantity of relatively dry grain approximately equal to 1/5 of its own body wt.

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