ABSTRACT
The reason for the unilateral development of female genital organs might be to reduce weight for flying (see discussion by Gilbert, 1979). The question than arises why the falconiforms allow themselves the luxury of two genital tracts. To reduce weight their hard-shelled eggs are perhaps relatively small and are laid down at an early stage of development. The weight of the egg in relation to the maternal body weight in falconiforms varies from 2.75% in the Whitetailed eagle, Haliaeetus albicilla (Accipitridae) to 8.5 % in Falco (Falconidae) and thus is at a lower level compared with non-falconiforms (Starck 1965). A relatively long incubation time and a small number of eggs laid are also found in falconiforms in comparison with other birds. Yet, these data do not yield an entirely satisfactory explanation for either a single or a double female genital tract. When ovulation occurs, the mature follicular oocyte is released from the ovary and is received by the oviduct. This tract surrounds the ovum with the albumen, the shell membranes, and the shell to form the characteristic avian
egg. In addition to forming and transporting the egg, the oviduct is the site of sperm storage, sperm transport, fertilization and early embryonic development. (See Chapter 11 for more details about the role of the oviduct in reproduction.).
