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14- Patel, M.D. (1936). The physiology of the formation of “pigeon’s milk”. Physiol. Zool. 9: 129-152.

15- Silver, It (1984). Prolactin and parenting in pigeon family. The Journal of Experimental Zoology, 232: 617-625.

16- Sturkie, P.D. (1976). “Avian Physiology” Springer-Verlag, Heidelberg.

17- Tudor. D.C. (1991). Pigeon Health and Disease. Ames, Iowa State University Press, pp 1-244.

18- Whitman, C.O. (1919). The behaviour of pigeons. Carnegie Inst. Wash. Publ. 257 (3): 1-161.