The Role of Invertebrates in the Diet, Growth and Survival of Northern Bobwhite, Colinus virginianus, Chicks in the Southeastern United States.

Abstract

Invertebrates are the primary component in the diet of northern bobwhite, Colinus virginianus, chicks during the first two weeks of life. Despite this, few studies have described the composition of invertebrates in the diet of wild chicks and none have examined their effects on chick-growth and survival. Here, a three-year study was conducted to examine the role of invertebrates in the diet of northern bobwhite chicks in the southeastern United States.
Initially, laboratory feeding-trials were conducted to evaluate the use of faecal analysis for studying the invertebrate diet of northern bobwhite chicks. Then, by accounting for differential recovery of prey items, the invertebrate diet of bobwhite broods on farmland and forested plantations in Florida and Georgia was determined by analysing faeces collected from their nocturnal roost sites. These broods were also captured at 10-days old to provide data on chick-growth and survival. Invertebrate-selection by bobwhite chicks was studied by comparing the composition of invertebrates in the diet of chicks to that found in brood-rearing habitats. In addition, the invertebrate-selection of human-imprinted chicks in the same habitats was also examined and compared to that of the wild chicks. Finally, because cotton is a major crop in the southeastern United States, a field-scale study was conducted to examine how crop-management differences between insect resistant and non-insect resistant cotton varieties affect the abundance of bob white chick-food invertebrates.
Invertebrate selection by both wild and human-imprinted chicks was non-random. Although invertebrate composition in the diet of chicks differed between all sites, the three invertebrate groups most selected by wild bobwhite chicks, Hemiptera, Coleoptera and Hymenoptera, collectively formed over 70% of the invertebrate-diet on all study sites. Although invertebrate-composition in the diet had no effect on chick survival, growth rates of chicks were lower in those broods that had a high proportion of the least selected prey items in their diet. The invertebrate selection of human-imprinted chicks was similar to that of wild chicks, suggesting that invertebrate selection by bobwhite chicks is innate. In the cotton study, half-fields planted to an insect resistant cotton variety received fewer applications of insecticide than those planted to a non-resistant variety. Consequently, a greater abundance of bobwhite chick-prey invertebrates were found in the insect resistant cotton crops. This study has identified those invertebrate groups most important in the diet of wild northern bobwhite chicks. Management prescriptions can now be designed and developed to specifically increase the abundance of these prey items within brood-rearing habitats.