Hourly locations and survival data of Nilgai Antelope (Boselaphus tragocamelus) in South Texas

Wildlife play 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, Rhipicephalus (=Boophilus)
microplus and R. (B.) annulatus. Although cattle fever ticks were
eradicated from the U.S. by 1943, bovine babesiosis and cattle fever ticks
are prevalent in México. Recently, management of cattle fever ticks in the
Texas-México region has been complicated by the presence of free-ranging,
exotic nilgai antelope (Boselaphus tragocamelus). Nilgai are abundant, are
competent hosts for cattle fever ticks, and make long-distance movements.
The goal of this study was to better understand nilgai movements and space
use to inform cattle fever tick treatment strategies. We analyzed hourly
locations from 40 GPS-collared nilgai in Cameron County, TX, USA, from
April 2019–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 calculated average movement
metrics, activity patterns, and space use of nilgai using the Euclidean
distance between locations. We observed movement patterns consistent with
residency (52.5%), seasonal movers (17.5%), dispersal (5%), and
unclassified (25%). Two young females made separate dispersal movements of
about 40 km from their initial capture location. Overall, nilgai had large
and highly variable home ranges: annual median home range estimate for
females was 563 ha (range = 105–1,545) and for males was 937 ha (range =
221–1,602). Peak nilgai movements occurred during crepuscular hours, and
median hourly movement for females was 57 m/hr and for males was 66 m/hr.
Nilgai home ranges and long-distance movements have the potential to
overlap multiple ranches, as the typical ranch size in South Texas ranges
from 250–6,000 ha. Female dispersal can increase the rate at which viable
nilgai populations can be established in new areas with implications for
disease spread and management. Understanding these behaviors will help the
Cattle Fever Tick Eradication Program develop more efficacious treatment
strategies to treat infestations in nilgai.