Red imported fire ants may be killing as many as a fifth of baby song birds before they leave the nest, according to research recently completed at Texas A&M University.
Andy Campomizzi, graduate research assistant in the department of wildlife and fisheries sciences, studied black-capped vireos and white-eyed vireos in Coryell County over a span of two years Campomizzi kept records on a total of 72 nests of both species. Of the nests where there was no pesticide treatment, only 10 percent of the young birds fledged and were able to leave the nests. Of the nests with treatment to protect them from fire ants, 32 percent fledged. Nearly 70 percent are lost to other causes, and fire ants knocked the survival rate down an additional 22 percent.
"That was a bigger difference than we thought it would be," he said. "Fire ants were definitely a mortality factor for song birds."
The black-capped vireo – which breeds only in the Edwards Plateau of Texas, a couple of areas in Oklahoma and northern Mexico – is an endangered species. The white-eyed vireo is found more extensively throughout the southeastern U.S. and is not endangered.
In his research, Campomizzi would find nests with eggs and attach Arinix – a nylon plastic cable wrap developed for use in protecting electrical equipment from fire ants – around branches. Some of the wraps were permeated with permethrin insecticide and some not.
A sticky insect trap coating was applied to the branch on the limbs with the insecticide, so the ants could not get around the trap to the nest, he explained. Nests were isolated so access was limited to one or two routes for the fire ants, he said.
He checked the nests every three or four days. He counted the nest as a success if the adults could raise at least one of their young until it could fly out of the nest, which takes about 10 to 12 days from hatching.
Campomizzi believes fire ant predation may occur among any song bird species, although mortality rates would vary depending upon local populations of the red imported fire ant and how close to the ground the birds were nesting.
Management for black-capped vireos is ongoing on both public and private land, he said.
"Current management includes providing breeding habitat and removing brownheaded cowbirds, a brood parasite," Campomizzi said.
Land managers interested in improving black-capped vireo habitat may want to consider managing fire ants around nesting areas to increase the chances that they can successfully raise their young. This will perhaps contribute to the species' recovery from being endangered, he said..
The research was funded by the Texas A&M Institute of Renewable Natural Resources.
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