Vulture-cattle interactions at a central Florida ranch
2004
Humphrey, John S. | Tillman, Eric A. | Avery, Michael L.
Black vulture depredations to newborn livestock, poultry, and other captive animals have been reported from at least 15 states, and during the 1990s, reports of depredations increased annually by an average of 18%. In response to this issue, we initiated a study at Buck Island Ranch of the MacArthur Agro-Ecology Research Center in central Florida to examine interactions between cattle and vultures. Based on previous reports, we hypothesized that vulture predation selectively targets calves of young, inexperienced cows. To document vulture activity, we conducted point counts of vultures in pastures throughout the ranch from January 2000 to March 2001. During point counts, turkey vultures accounted for 78% of the observations compared to 22% for black vultures. We noted that vultures used certain pastures preferentially, with over 70% of the vultures in 3 pastures where heifers were calving and the remainder spread among 7 pastures containing yearling heifers only or cows and calves. Turkey and black vultures were often present during the 19 calving events we observed, but usually neither species exhibited threatening behavior toward calves or calving heifers. Instead, the birds seemed intent on gaining access to the afterbirth. On one occasion, however, we observed an attempted depredation by black vultures on a calf as it was being born. The cow was able to chase the buds off, however, and the birth proceeded successfully. We conclude that predation by black vultures occurs when the buds identify and then exploit vulnerable animals, although there is still much to be learned regarding the circumstances that promote such activity. Current management recommendations include dispersing nearby black vulture roosts and providing careful oversight to protect inexperienced cows that are first-time breeders.
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