Movement strategies and behavior of Nilgai antelope: Implications for Cattle Tick management in South Texas

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

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/24/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cattle fever ticks (CFT) Rhipicephalus microplus and R. annulatus are invasive livestock pests that are endemic to Mexico and invasive along the Texas – Mexico border. Acaricide resistance, alternate wildlife hosts, and pathogenic landscape forming weeds present challenges for sustainable eradication of this pest in the U.S. CFT are the vector for bovine babesiosis, a lethal disease causing high mortality particularly in cattle. Efforts to eradicate CFT from the United States have been successful; however, in recent years, there has been an increase in CFT infestations outside of the Permanent Quarantine Zone in Texas. One of the alternate wildlife hosts for CFT in South Texas are nilgai (Boselaphus tragocamelus), an exotic Asian bovid. Nilgai are highly mobile with large home ranges and are implicated in the spread of CFT, through the landscape. Insect and tick killing parasitic round worms (entomopathogenic nematodes) are under evaluation for eradication of CFT on nilgai. Nematodes can be applied as a water-based spray to nilgai. A remotely activated field sprayer was developed for application of nematodes on CFT infested nilgai as they transit fence crossings. The goals of this study were to 1) assess movement strategies of individual nilgai, 2) estimate home range sizes at different temporal scales (monthly, seasonally, and overall), and 3) calculate average movement metrics of nilgai to assess activity patterns and space use. We used hourly locations from 30 GPS-collared individuals to help understand nilgai movement behaviors. Movement strategies included dispersal (6.7%), use of seasonal ranges (23.3%), nomadic movements (13.3%), and resident (56.7%). Two young females made long-distance movements, traveling ~40 km from their initial capture location. Overall, nilgai had large and highly variable home ranges: annual median home range estimate for females was 593 ha (105–1,545) and for males 937 ha (221–1,602). Peak nilgai activity occurred during the morning and evening hours, and average movement for females was 126 m/hr and for males 152 m/hr. Large home ranges and long-distance movements by nilgai challenge the sustainability of CFT eradication efforts in the U.S.

Technical Abstract: Wildlife play an important role in the emergence of livestock diseases and can complicate disease management efforts. One of the most significant tick-borne diseases of livestock worldwide is bovine babesiosis, which is at risk of spreading from wildlife hosts to cattle. The Southern Cattle Fever Tick (CFT), Rhipicephalus microplus, is a vector of the pathogens that cause bovine babesiosis in cattle. Nilgai antelope (Boselaphus tragocamelus) are an exotic ungulate with over 30,000 free-ranging individuals in South Texas. Nilgai are a competent host for CFT. Nilgai infested with CFT can complicate eradication efforts because their ecology involves long-distance movements. The goals of this study were to 1) assess movement strategies of individual nilgai, 2) estimate home range sizes at different temporal scales (monthly, seasonally, and overall), and 3) calculate average movement metrics of nilgai to assess activity patterns and space use. We used hourly locations from 30 GPS-collared individuals to help understand nilgai movement behaviors. Movement strategies included dispersal (6.7%), use of seasonal ranges (23.3%), nomadic movements (13.3%), and resident (56.7%). Two young females made long-distance movements, traveling ~40 km from their initial capture location. Overall, nilgai had large and highly variable home ranges: annual median home range estimate for females was 593 ha (105–1,545) and for males 937 ha (221–1,602). Peak nilgai activity occurred during the crepuscular hours, and average movement for females was 126 m/hr and for males 152 m/hr. Large home ranges and long-distance movements by nilgai challenge the sustainability of CFT eradication efforts in the U.S.