Mortality rates have been well observed in birds; there have been instances where no young have survived to adulthood in areas with high fire ant density. Many birds including cliff nesting swallows, ducks, egrets, quail, and terns have been affected by red imported fire ants. Ground nesting birds, particularly the least tern ("Sterna antillarum"), are vulnerable to fire ant attacks. The impact of red imported fire ants on colonial breeding birds is especially severe; waterbirds can experience a mortality rate of 100%, although this factor was lower for early-nesting birds. Brood survival decreases in American cliff swallows ("Petrochelidon pyrrhonota") if they are exposed to foraging workers. Songbird nest survival decreases in areas with red imported fire ants present, but survival rates in white-eyed vireo ("Vireo griseus") and black-capped vireo ("Vireo atricapilla") nests increase from 10% to 31% and 7% to 13% whenever fire ants are not present or when they are unable to attack them. Red imported fire ants may indirectly contribute to low brood survival in the Attwater's prairie chicken. It was first thought that the ants were linked to the decline of overwintering birds such as the loggerhead shrike ("Lanius ludovicianus"), but a later study showed that ant eradication efforts using the pesticide Mirex, which was known to have toxic side effects, was largely to blame.