Multiple parasitism is likely to be costly for Baywings because Screaming and Shiny cowbirds often puncture host eggs during nest visits, which may reduce host clutch size even in unparasitized nests (Hoy and Ottow 1964, Fraga 1998, Massoni and Reboreda 2002, Astie and Reboreda 2006).
We observed nest reuse in 51/ 51 cases within breeding seasons when the nest failed due to clutch ejection by hosts in response to multiple parasitism, but we only observed nest reuse in 1/46 cases when the nest failed due to predation.
Thus, multiple parasitism can arise as a consequence of a limitation of suitable nests, high fecundity rates of female cowbirds, or high population density of the parasite relative to the number of host breeding pairs (Martinez et al.
Spatial patterns of egg laying and multiple parasitism in a brood parasite: a non-territorial system in the Great Spotted Cuckoo (Clamator glamdarius).
Genetic and temporal patterns of multiple parasitism by Brown-headed Cowbirds (Molothrus ater) on Song Sparrows (Melospiza melodia).