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Blockstein, David E. (1989). "Crop milk and clutch size in mourning doves". The Wilson Bulletin. 101 (1): 11–25. JSTOR4162684. The fact that none of the nearly 300 species of Columbiformes has a clutch size larger than two eggs suggests that there is limited plasticity in crop-milk production.
Vandeputte-Poma, J.; van Grembergen, G. (1967). "L'evolution postembryonnaire du poids du pigeon domestique". Zeitschrift für vergleichende Physiologie (in French). 54 (3): 423–425. doi:10.1007/BF00298228. S2CID32408737.
stanford.edu
Ehrlich, Paul R.; Dobkin, David S.; Wheye, Darryl (1988), "Bird Milk", stanford.edu