Movement ecology of exotic nilgai antelope: A threat to the re‐emergence of cattle fever ticks in the southern USA

Abstract

Wildlife plays an important role in the emergence of livestock diseases, and their movements can complicate disease management efforts. One of the most significant vector-borne diseases of livestock worldwide is bovine babesiosis, spread by cattle fever ticks (CFTs; Rhipicephalus [=Boophilus] microplus and Rhipicephalus [=Boophilus] annulatus). Although CFTs were eradicated from the United States by 1943, bovine babesiosis and CFTs are prevalent in México. Recently, management of CFTs in the Texas-México region has been complicated by the presence of free-ranging, exotic nilgai antelope (Boselaphus tragocamelus). Nilgai are abundant in this region and are competent hosts for CFTs. The goal of this study was to better understand nilgai movements and space use to inform CFT treatment strategies. We analyzed hourly locations from 40 GPS-collared nilgai in Cameron County, TX, USA, from April 2019 to September 2020. We assigned each nilgai a movement behavior using the net squared displacement metric. We estimated nilgai home range sizes at different temporal scales (monthly, seasonally, and overall) using Brownian bridge movement models. We observed movement patterns consistent with residency (52.5%), seasonal movers (17.5%), dispersal (5%), and unclassified (25%). Resident nilgai had an average maximum axial distance of 7.8 km, while two young females made separate dispersal movements of about 40 km within a year. Overall, nilgai had large and highly variable home ranges: annual median home range estimate for females was 563 ha (range = 105-1545 ha), and for males, it was 937 ha (range = 221-1602 ha). Peak nilgai movements occurred during crepuscular hours, and median hourly movement for females was 57 m/h, and for males, it was 66 m/h. Nilgai home ranges and long-distance movements have the potential to overlap multiple ranches, as the typical ranch size in South Texas ranges from 250 to 6000 ha. Resident nilgai were more likely to maintain local infestations of CFT. Dispersal events took place during peak tick season, demonstrating the potential for nilgai to

Nilgai antelope display no signs of infection upon experimental challenge with a virulent Babesia bovis strain

“…microplus in this area [11,12] as well as in the Tick Eradication Quarantine Area that is an integral region within the CFTEP [5,15]. The documented long-range movement of nilgai antelope [13,35] increases the possibility that these nilgai could transport infected ticks originating from Mexico, where B. bovis and B. bigemina are endemic. Given the overlapping habitat of alternative hosts with primary cattle hosts, it is imperative to understand the impacts of exotic species that are a new addition to the ecology and epidemiology of this disease system.…”

“…microplus in this area [ 11 , 12 ] as well as in the Tick Eradication Quarantine Area that is an integral region within the CFTEP [ 5 , 15 ]. The documented long-range movement of nilgai antelope [ 13 , 35 ] increases the possibility that these nilgai could transport infected ticks originating from Mexico, where B . bovis and B .…”

“…These species are viable alternative hosts for cattle fever ticks, as the ticks can reproduce on these hosts [8][9][10], and various life stages of the tick have been recovered from them [11,12]. As such, they provide a dispersal mechanism for ticks, as they can travel large distances and occupy areas previously free of cattle fever ticks [13][14][15]. Further, wildlife can readily cross the border between Mexico and the USA [16].…”