Bait-delivered cabergoline for the reproductive control of the red fox (Vulpes vulpes): estimating mammalian non-target risk in south-eastern Australia

Abstract

Cabergoline (CAB) is a potent dopamine agonist and an inhibitor of prolactin (PRL). In red foxes (Vulpes vulpes), a single oral dose of 100 g kg^–1 CAB can cause abortions and postnatal cub mortality from at least Day 21 of the 52-day pregnancy. The abortifacient activity of CAB is owing to the suppression of PRL, which is essential for luteotrophic support in some eutherian species. Postnatal cub mortality probably results from a reduction in the development of the mammary ductile system, which is also partially dependant on PRL during pregnancy. This paper investigates the potential risks faced by non-target mammalian species that may consume CAB baits intended for fox control. Baiting with CAB is proposed from 1 August until 1 October each year, to correspond with the time that most vixens are pregnant in south-eastern Australia. Thirty-four endemic mammals in south-eastern Australia (9 eutherians and 25 marsupials) are considered to be potentially bait-consuming (PBC) species. The percentage overlap of pregnancy and birth periods for each PBC species was compared with the duration of the proposed CAB baiting period. Only Antechinus (3 species) and Sminthopsis leucopushave greater than 40% overlap, whereas overlap in endemic rodents ranges from 0% to 22%. Overall, most PBC rodent populations appear to face little risk from CAB baiting, as their period of pregnancy does not overlap significantly with the proposed CAB baiting period. The Antechinus species, Phascogale tapoatafa and Dasyurus maculatus are the only PBC mammals that are seasonally mono-oestrous and are thus probably more susceptible to disruption of breeding compared with polyoestrous species that may breed many times a year. At a baiting density of 8 baits km^–2, theoretical bait availability for small dasyurids, rodents and peramelids is low. This suggests a low potential for affecting these populations if CAB was indiscriminate in affecting reproductive success in all mammal groups. Presently, studies in a limited range of marsupials suggest that, unlike eutherians, the marsupial corpus luteum is independent of pituitary control and thus suppression of PRL is not likely to cause abortions in marsupials. As yet, CAB has not been shown to be orally active in any PBC species other than rodents and carnivores. Oral doses of CAB given post partum have not been found to affect lactation in Sminthopsis crassicaudata,Trichosurus vulpecula, Macropus eugenii andSetonix brachyurus. Further studies are required in order to assess the potential for high doses of oral CAB to affect pre-partum mammary development and early lactation post partum, especially in peramelids and larger dasyurids. Highly target-specific baiting techniques, may eliminate most PBC species from being exposed to CAB and these are briefly discussed.