THE BREEDING BIOLOGY OF THE PIED WATER-TYRANT AND ITS INTERACTIONS WITH THE SHINY COWBIRD IN VENEZUELA

We studied the breeding biology of the Pied Water-Tyrant (Fluvicola pi ca) in a seasonally inundated savanna in the Ilanos of western Venezue la. A total of 123 nests was located in the wet season (June-October). The water-tyrant nested mainly in trees and shrubs near water in the early part of the wet season (86%), but nested primarily in emergent m arsh vegetation during the latter parr (84%). The species was heavily parasitized (53% of nests) by the Shiny Cowbird (Molothrus bonariensis ). The rate of parasitism was nearly equal in both tree/shrub nests an d marsh nests, and declined only late in the season. Parasitized nests were more frequently abandoned (60%) than nonparasitized nests (30%). The number of host eggs in nests was nearly equal in non-parasitized (2.42) and parasitized nests (2.51). The number of cowbird eggs (1.23) was less than the number of host eggs in parasitized nests. Of 37 non -parasitized clutches of the Pied Water-Tyrant, 18 (49%) produced nest lings and 7 (19%) produced fledglings, and of 47 parasitized clutches, 2 (4%) produced nestlings and fledglings. Given the high level of par asitism on the Pied Water-Tyrant, it should be considered a major Shin y Cowbird host in the Ilanos of Venezuela. The Pied Water-Tyrant, howe ver, does not appear to be an optimal host as only 3 of 47 parasitized nests in which the outcome was known successfully fledged cowbird you ng.