Assessing physiological, behavioral and movement responses to Suprelorin® implant delivery methods in free-ranging eastern grey kangaroos (Macropus giganteus)

Overabundant populations of eastern grey kangaroos (Macropus giganteus) in
peri-urban areas pose ecological and social challenges. Current management
strategies are often hindered by animal welfare and logistical concerns.
This study aimed to assess stress responses of kangaroos to two
contraceptive delivery methods. We assessed physiological and behavioral
responses of females treated with Suprelorin® (deslorelin acetate)
implants delivered remotely as an alternative to the traditional
capture-treatment method. Sexually mature females were assigned to one of
three groups: SC (4.7 mg implant via subcutaneous injection after
capture), Dart (4.7 mg implant remotely via dart), and Control (no
treatment or capture). We used a before-after control-impact framework to
quantify stress-induced response to both methods through assessment of
changes in behavior (which may also indicate pain) and fecal
glucocorticoid metabolite (FGM) concentrations. Additionally, we assessed
changes in movement patterns using GPS collars. No significant changes in
FGM concentrations, behavior, or movement were detected across treatments
or time periods. During the treatment window (5-9 April 2018), the Dart
group displayed a temporary reduction in step length while the SC group
shifted from nocturnal to crepuscular activity, with both groups returning
to pre-treatment patterns after the treatment window. The SC group showed
weak evidence of increased vigilance and decreased grooming throughout the
treatment window, though individual variability was high. Remote dart
delivery avoids risk associated with sedation and capture and imposes
fewer behavioral disruptions, presenting a safer alternative for
administering injectable contraceptives to kangaroos in a peri-urban area.
Therefore, remote delivery offers a less invasive, more welfare-friendly
and practically advantageous option for managing overabundant populations.
Future research should enhance the utility of remote delivery by
addressing logistical challenges (e.g., identifying treated animals) and
evaluating efficacy in other species. Adoption of remote delivery
contraceptives in wildlife management policies could enhance ethical and
practical management of overabundant populations.