Northern Bobwhite Chick Mortality Caused by Red Imported Fire Ants

Abstract

Northern bobwhite (Colinus virginianus) populations have declined throughout their range during the last 30 years. Change in land management is thought to be a primary cause of this decline, but the invasion of northern bobwhite habitats by the red imported fire ant (Solenopsis invicta) also may be involved. We compared hatching success and subsequent survival of wild northern bobwhite chicks on the Coastal Prairie of Texas in 1997 and 1998 between broods that hatched under natural conditions or following fire ant suppression treatments. In 1997, the fire ant suppression treatment resulted in a 70% reduction in the number of red imported fire ants on baits placed in treated nests on the day after hatch. Using 2 fire ant suppression treatments in 1998 reduced the number of red imported fire ants on baits by >99%. No year or treatment × year interaction effects were detected for hatching success or survival, and no treatment effect was detected for hatching success (P > 0.10). However, the proportion of chicks surviving to 21 days was higher (P = 0.010) for treated nests (n = 18) than control nests (n = 25; proportions of broods surviving: 53.5 8.6% [x SE] vs. 24.7 ± 6.6%; chick survival: 60.1 ± 7.6% vs. 22.0 ± 6.2%). The probability of chick survival decreased (P < 0.001) as our index of red imported fire ant activity in the nest increased. These results indicate northern bobwhite chicks can suffer high levels of mortality due to red imported fire ants, which could explain declines in some northern bobwhite populations following infestations by red imported fire ants. Current methods for controlling red imported fire ants are expensive and may last <3 months. Thus, strategies for mitigating the effect of red imported fire ants to northern bobwhite populations in this area should probably focus on reducing other mortality factors or increasing productivity.