Movements and home range sizes of nilgai antelope: Implications for management of cattle fever ticks in South Texas

Authors: SLIWA, KATHRYN - Texas A&M University; BAUMGARDT, JEREMY - Texas A&M University; DEYOUNG, RANDALL - Texas A&M University; ORTEGA-S, ALFONSO - Texas A&M University; HEWIIT, DAVID - Texas A&M University; Goolsby, John; Perez De Leon, Adalberto - Beto

Submitted to: The Wildlife Society
Publication Type: Proceedings
Publication Acceptance Date: 9/27/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Nilgai antelope are implicated in the long-range movement of the southern cattle fever tick (SCFT), Rhipicephalus microplus, especially in Cameron and Willacy Counties in South Texas. This research was conducted to: 1) determine seasonal home-range sizes of nilgai using hourly locations from 26 satellite-collared individuals; and, 2) examine nilgai movement behaviors. Overall, nilgai had large and highly variable home ranges. Two young female nilgai made long-distance movements of over 40 kilometers within a month, sometimes traveling 2-5 km/hr. These movements resemble dispersal behavior which is not common for female hoofed animals and may result from the social structure of nilgai where males are territorial. Large home ranges and long-distance movements are clearly an obstacle for SCFT management. These research outcomes enhanced our understanding of nilgai movements in South Texas. The scientific knowledge generated through this study can be adapted by the Cattle Fever Tick Eradication Program to keep the U.S. SCFT-free.

Technical Abstract: In 1906, the Cattle Fever Tick Eradication Program was created by the USDA to combat the tick vectors of bovine babesiosis. Rhipicephalus (Boophilus) microplus and R. (B.) annulatus, collectively known as cattle fever ticks (CFT), can still be found in the borderlands between South Texas and Mexico. Bovine babesiosis is endemic to Mexico, threatening U.S. cattle herds with disease. Wild ungulates, such as nilgai antelope (Boselaphus tragocamelus), can complicate CFT eradication because these alternative host species have the ability to make long-distance movements. Nilgai are an exotic species introduced to South Texas in 1924, and have since spread throughout the region. Its current population size is estimated to be 30,000-50,000 individuals. A previous study suggested nilgai have large home range sizes, however little is currently known on this topic. The goals of this study were to: 1) determine seasonal home range sizes of nilgai using hourly locations from 26 GPS-collared individuals; and 2) examine nilgai movement behaviors. Overall, nilgai had large and highly variable home ranges: males (n=9), median = 693 ha (range=76–4677 ha), females (n=15) median = 529 ha (range=29–5611 ha). In our study, 2 young females made long-distance movements of over 40 km within a month, sometimes traveling 2-5 km/hr. These movements resemble dispersal behavior which is not common for female ungulates, and may result from the social structure of nilgai, in which males are territorial. Large home ranges and long-distance movements are clearly an obstacle for CFT management. With the frequent invasion of CFT, a better understanding of nilgai movements will provide key information needed to eradicate this tick vector.