The Indigobirds and Whydahs (Vidua) and the Cuckoo Finch (Anamalospiza) are small passerine birds native to Africa. They are all brood parasites which lay their eggs in the nests of estrildid finches.
Occasional host shifts can possibly lead to hybridization, for example hybrids between Long-tailed Paradise Whydah (V. paradisaea) and Village Indigobird (V. chalybeata) and hybrids between Long-tailed Paradise Whydah and Purple Indigobird (V. purpurascens) have been attributed to accidental host shifts (Payne, 1980; Payne & Sorenson, 2004). But mostly hybridization is not so frequently as to prevent speciation (Sefc, Payne & Sorenson, 2005). Indeed, speciation following a host shift has been documented (Sorenson, Sefc & Payne, 2003). However, a host shift does not immediately leads complete reproductive isolation. Two recently formed host races of the Cameroon Indigobird (V. camerunensis) still exchange genetic material (Balakrishnan, Sefc & Sorenson, 2009).
Balakrishnan, C. N., Sefc, K. M. & Sorenson, M. D. (2009). Incomplete reproductive isolation following host shift in brood parasitic indigobirds. Proceedings of the Royal Society B-Biological Sciences 276, 219-228.
Payne, R. B. (1980). Behavior and Songs of Hybrid Parasitic Finches. Auk 97, 118-134.
Payne, R. B. & Sorenson, M. D. (2004). Behavioral and genetic identification of a hybrid Vidua: Maternal origin and mate choice in a brood-parasitic finch. Auk 121, 156-161.
Sefc, K. M., Payne, R. B. & Sorenson, M. D. (2005). Genetic continuity of brood-parasitic indigobird species. Molecular Ecology 14, 1407-1419.
Sorenson, M. D., Sefc, K. M. & Payne, R. B. (2003). Speciation by host switch in brood parasitic indigobirds. Nature 424, 928-931.