Suchergebnisse

Context
Feral horses are a growing problem in Australia, despite implementation of management strategies. The incidence of horse sightings and horse-associated vehicle collisions within the Tuan and Toolara State Forest (TTSF), a coniferous plantation in south-eastern Queensland, has increased in the past decade, indicating an increase in population and the necessity to undertake an accurate appraisal of population abundance.

Aim
To determine the feasibility of using dung counts, defecation and dung-decay rates to determine the distribution and abundance of feral horse population in a managed coniferous plantation where dense vegetation prohibits the use of visual-based animal detection methods.

Methods
Population distribution was assessed by dung count incorporated into a vehicle strip-transect survey on 582 km of forest tracks. Population abundance was estimated from dung density, the mean defecation frequency of feral horses, and the mean number of days required for dung to decay. Dung density was obtained from on-ground distance line-transect survey that sampled all representative plantation habitats and consisted of 111 transects totalling 44.3 km.

Key results
The strip-transect survey clearly showed that although feral horses were dispersed across the plantation, the distribution was uneven, with the central region of the plantation being the most heavily populated. The combination of dung counts, defecation rate (mean ± s.d., 7.97 ± 8.74) over 24 h and dung-decay rate (444 ± 150.7 days) provided an estimation of the density of feral horses in various habitats and indicated that the plantation was occupied by 1321 (95% CI 940–1965) horses, which corresponded to an average density of 1.8 horses km–2. The method clearly identified variations in horse abundance among the various habitats within the surveyed areas. Open habitats, created following harvesting, showed higher occurrence rates, whereas the habitats of mature forest were scantily occupied.

Key conclusions
Dung counts are a simple, effective and practical technique that can provide information on distribution and abundance of feral horse population in densely forested habitats where visual-based techniques are not applicable. However, unbiased and precise defecation and decay rates must be estimated.

Implications
The study validated the use of dung counts to provide information on feral horse distribution and abundance in densely forested environments where direct methods of census may be difficult to obtain. The methods are applicable to a range of ecosystems, but defecation and dung-decay rates must be determined separately for each ecosystem.

Context Understanding population dynamics of invasive species is crucial for the development of management strategies. Feral horses (Equus caballus) are a growing problem in the Tuan–Toolara State Forest (TTSF), a coniferous plantation in south-eastern Queensland, Australia. Aim The population dynamics of the TTSF feral horses was not known. Therefore, the study was designed to characterise the major vital parameters of this population and, using these data, develop a long-term management plan. Methods The study was conducted over 3 years (2011–14) involving 522 individually identified horses. Foaling rates were used to calculate fecundity. Body fat distribution was estimated using body condition score (BCS), which reflects the nutritional, metabolic and general health of individual animals. Multi state mark–capture population models were used to estimate age-specific survival, and the Leslie age-structured projection matrix model was used to determine the annual rate at which the population increased. Key results The mean annual fecundity was low (0.23 ± 0.07 s.d.). The mean BCS of the population was mid-range (2.55 ± 0.51 s.d.) with adult females having lower scores than other age and gender groups. Survival estimates were consistently high (0.92–0.95) across all age groups. The average annual finite rate of population increase (λ) for the 3 years of the study was 1.09. Sensitivity analysis demonstrated that the population growth rate was almost seven times more sensitive to changes in adult survival compared with juvenile survival, and almost twice as sensitive to changes in fecundity. Key conclusions Population dynamics of the TTSF feral horses were comparable to other feral horse populations similarly challenged by environmental nutritional limitations. Implications Defining population dynamics of the TTSF feral horses permits the formulation of management goals that can be audited and adapted as required. The most effective strategy for controlling population growth in the TTSF would involve the continuing removal of substantial numbers of adult females or manipulation of survival and/or fecundity. As selective removal will likely alter the adult sex ratio and age structure of the population, ongoing assessment is necessary to minimise adverse welfare outcomes.

Context The study of any wild animal's home range requires the collection of spatiotemporal data, obtained independently of climatic conditions or time of day. This can be achieved by the attachment of global positioning system (GPS) data loggers, which, in large species, is best achieved by remote immobilisation. Feral horses (Equus caballus) usually occupy remote areas of Australia; however, a considerable population increase has been observed in a close proximity to metropolitan areas of the Australian east coast, creating increasing conflict with human interests. Aim The aim of the present study was to investigate the efficacy of remote chemical immobilisation of feral horses with medetomidine combined with tiletamine–zolazepam to facilitate placement of satellite GPS collars. Methods Nine feral horses were darted from the ground with 60 mg (i.m.) medetomidine and 1500 mg (i.m.) tiletamine–zolazepam. The effects of medetomidine were reversed with 50–100 mg (i.m. or i.v.) atipamezole 30–40 min after induction (IV/IM). Physiological variables monitored during anaesthesia were heart rate, respiratory rate, temperature and oxygen haemoglobin saturation (Spo2). Key results All horses were successfully immobilised with between one and three darts (n = 9). The mean (± s.e.m.) dose of medetomidine was 0.15 ± 0.01 mg kg–1, whereas that of tiletamine–zolazepam was 3.61 ± 0.16 mg kg–1. Mean time from darting to lateral recumbency was 13.3 ± 2.7 min and mean recumbency time was 54 ± 13 min. Vital signs for all anaesthetised animals remained within the normal range during anaesthesia, with the exception of one animal exhibiting a transient drop in Spo2. There were no deaths. Key conclusions The combination of medetomidine and tiletamine–zolazepam provided adequate anaesthesia in feral horses in the field for application of GPS collars. Implications Although a limited number of horses was immobilised, the present study shows that the combination of medetomidine and tiletamine–zolazepam provides effective short-term anaesthesia for feral horses, affording a practical and field-accessible capture technique. This method could also be applied to other management actions requiring the safe and humane capture of feral horses.