The Giant Cowbird is a tropical species which specializes on parasitizing the nests of Oropendolas and Caciques. It is known to search for insects on the backs of Capybaras (Hydrochoerus hydrochaeris) to rid them of horse flies (Tabanidae). In this photo the Capybara seemed to enjoy it immensely. Thus we have the world's largest cowbird preening the world's largest rodent. Eye color in the Giant Cowbird is variable. It is dark in immatures but light yellow to red or orange in adults. Two subspecies currently recognized with the larger nominate race occurring in South America. Clements considers M. o. violeus a synonym and some authors consider the species to be monotypic.
References:
Jaramillo, A., and P. Burke. 1999. New World blackbirds. The icterids.
Princeton University Press, Princeton, NJ.
Lowther, Peter E. 2010. Giant Cowbird (Molothrus oryzivorus), Neotropical
Birds Online (T. S. Schulenberg, Editor). Ithaca: Cornell Lab of
Ornithology; retrieved from Neotropical Birds Online.
Nikon P510