Abstract: This field study of feral stallions in Montana and Idaho examines and correlates the seasonal pattern of plasma androgens and specific sociosexual behaviour and reports the effect of a long-acting androgenic steroid on this behaviour and on fertility. Plasma testosterone was measured by competitive protein binding assay in samples obtained by jugular venepuncture from captured animals. In samples taken from 34 sexually mature stallions in 6 different months during the year, a definite seasonal pattern in testosterone was present, with a peak in May (3.04 +/- 0.63 ng/ml) and a nadir in December (1.55 +/- 0.34 ng/ml). Values were less than 2.0 ng/ml in non-breeding months and greater than 2.4 ng/ml in breeding months. Behavioural endpoints measured were (1) stallion scent marking in response to elimination by mares (elimination marking), (2) mounting and (3) copulation. The frequencies of each of these endpoints followed closely the seasonal pattern seen for plasma androgens. In the fertility study microcapsulated testosterone propionate (microTP) was administered i.m. to 10 harem stud stallions 3 months before the 1980 breeding season. In these stallions and in 10 control harem studs, the above behavioural endpoints were examined in the 1980 and 1981 breeding seasons, and foal counts were made in 1981. There were no direct inhibitory or stimulatory effects of microTP treatment on any of the behavioural endpoints in either year. In 1981 foals were produced in 87.5% of the control bands and 28.4% of the microTP-treated bands. These results indicate that microencapsulated testosterone propionate can provide effective fertility control in feral horses without causing significant alterations in sociosexual behaviour.

Abstract: Patterned string tasks are a test of perceptual capacity and the understanding of means-end connections. Primates can solve complex forms of this task in laboratories. However, this may not indicate the level of such cognition that is commonly employed in the wild, where decision-making time is often short and distractions such as predator avoidance and competition between conspecifics are often prevalent. The current study tests whether wild common marmosets (Callithrix jacchus) can successfully complete the simplest form of the patterned string task, parallel strings, while in their natural environment. Although 12 out of 13 marmosets could successfully complete the task, in previous laboratory-based studies on primates, the errors at this task by all primate species tested were consistently lower than in the present study. This is probably explained by the added difficulties imposed by the natural setting of the task in the present study, exemplified by a significant increase in observed vigilance behaviour by subject animals prior to attempts at the task that were unsuccessful. The undertaking of such tasks by common marmosets in situ probably provides a more reasonable representation of the levels of cognitive capacity expressed by this species in the wild than do laboratory-based studies of the task.

Abstract: Contraception is becoming a common approach for the management of captive and wild ungulates yet there are few data for contraceptive effects on entire populations. Management-level treatment of mares with porcine zona pellucida (PZP) vaccine resulted in zero population growth of the Assateague Island wild horse population within 1 year of initiation of treatment. Contraceptive efficacy was 90% for mares treated twice in the first year and annually thereafter. For mares given a single initial inoculation, contraceptive efficacy was 78%. The effort required to achieve zero population growth decreased, as 95, 83 and 84% of all adult mares were treated in each of the first 3 years, compared with 59 and 52% during the last 2 years. Mortality rates for mares and foals after the initiation of management-level treatments decreased below historic and pretreatment mortality rates of approximately 5%. Two new age classes have appeared among treated animals (21-25 years and > 25 years), indicating an increase in longevity among treated animals. Body condition scores for all horses, all adult mares and non-lactating mares increased significantly between summer 1989 and autumn 1999 but did not change significantly in lactating mares. These results provide reliable data for the construction of realistic models for contraceptive management of free-roaming or captive ungulate populations.