| Using both an aviary and radiotelemetry on wild populations, I experimentally manipulated northern bobwhite (Colinus virginianus) covey group size to investigate its effect on (1) vigilance behavior, (2) predator detection, (3) feeding efficiency and mass change, (4) the existence of a stable covey size, (5) the effect of movement in maintaining a stable covey size, (6) covey persistence in relation to covey size, (7) individual survival in relation to covey size, and (8) the effect of harvest on coveys. I conducted research on 12 independent 259 ha study areas (6 control areas where 0% of the population was removed and 6 treatment areas where 60% of the population was removed) in east central Kansas between 8 November--31 January, 1997--00. Small groups (≤7 individuals) had reduced group vigilance, slower predator detection time, lower group persistence and lower individual survival. Small coveys used increased movement to create or join larger groups where survival was higher. Large groups (>15 individuals) had higher group vigilance and increased time to predator detection, however had lower individual survival, increased group movement, and individual mass loss. It is possible that density-dependent feedbacks (e.g. lower survival and increased competition) lowered larger coveys to a stable size. A stable covey size of 11 birds was promoted by high group persistence, low group movement, improved feeding efficiency, and improved individual survival from predation. My results suggest that the occurrence of local movement acts as a compensating factor to density reduction. Therefore, natural mortality pressure remained constant on each covey indicating harvest was an additive form of mortality. Additionally managers should note when monitoring bobwhite populations, covey size is a misleading measure of density. |
