Changes in photoperiod cause correlated changes in testes, cloacal glands, cloacal foam, and reproductive behavior of male Japanese quail. The cloacal protrusion may serve as a convenient external index of androgen, permitting repeated measurement without operation on or killing of the animal.

https://science.sciencemag.org/content/sci/157/3785/201.full.pdf

Photoperiodic Control of the Cloacal Gland of the Japanese Quail

Pituitary gonadotropins in the Japanese quail (Coturnix coturnix japonica) during photoperiodically induced gonadal growth

/pdf/histological-changes-in-the-regressing-reproductive-organs-b0zlfmkfo0.pdf

Mather B

Papers

Testicular response to gonadotropins and intermittent light in coturnix reared under limited light.