The resolution of conflicts between human and wildlife interests often involves lethal control to reduce problem wildlife populations. However, lethal control has always had its limitations, the acceptable methods are becoming fewer, and public opposition is on the increase. Fertility control offers a potential alternative approach that is widely regarded as being inherently more benign. Furthermore, in some circumstances fertility control may have specific advantages over culling. The development of “single-shot” injectable immunocontraceptive vaccines that inhibit the fertility of individual animals for several years is leading to practical applications that exploit this novel technology. Further advances can be expected to lead to the emergence of a new generation of wildlife management tools. A key issue in this process is predicting what the population consequences will be for a particular species, given a specific level of induced infertility. Here, we use population modelling techniques to explore how much fertility control is enough to achieve different levels of population reduction, how long it will take to realise these reductions, and to understand how these effects are shaped by the population biology of the target species. This offers some generic conclusions, with low levels of infertility having little impact on species with high population turnover rates, while modest levels of infertility may yield useful population reductions for species with low intrinsic rates of increase, although such effects take longer to be realised in long-lived species. We also observed that there is potential for optimising the intensity of induced infertility, in terms of the proportion of breeding animals rendered infertile, and the frequency of application; so, for instance, biennial application could be more efficient than annual application for some forms of fertility control in certain species. There is increasing evidence from field studies that the survival of infertile animals is enhanced, probably because they do not incur the costs of reproduction. Our model predicts that this effect will be of limited importance for short-lived species with high intrinsic rates of increase, but it is more likely to compromise population reduction in long-lived species. We suggest that the generic modelling approach can help develop an evidence-based platform for discussing when fertility control can be regarded as a feasible, desirable, and sustainable option to manage problem wildlife.

There is increasing demand for benign approaches to the resolution of conflicts between human interests and wildlife. One non-lethal method to reduce the growth and expansion of overabundant wildlife populations is fertility control. Significant progress has been made in recent years on the development of fertility control agents, culminating in the availability of single-dose injectable immunocontraceptive vaccines that inhibit the fertility of individuals for several years. The potential application of such technology is explored here using the European rabbit, gray squirrel, wild boar, and European badger as examples of species that pose problems of damage to agricultural and forestry interests, disease transmission and threats to biodiversity. A simple model is developed that predicts the likely general population consequences of varying levels of infertility for species with differing demographic characteristics. This suggests that low levels of fertility control will have little impact on population size in species with high reproductive rates and high population turnover rates. Modest levels of infertility can significantly reduce the populations of species with relatively low intrinsic rates of increase. However, these reductions may take longer than those arising from high levels of imposed infertility in species with rapid population turnover rates. The modeling approach, as outlined here, could be used to inform future field studies by identifying suitable target species and making predictions about population responses that can be tested empirically. These studies will be necessary to realize the potential of the emerging fertility control technologies in the form of practical wildlife management applications.

Food security and international trade require healthy livestock. A wildlife reservoir can compromise control of livestock disease. When disease is suspected in wildlife, initial questions include whether their behaviour, ecology and proximity to livestock pose a significant risk. Then, what options are there for mitigating risk? If we respond, how should we measure success? Following action, lessons must be learned so that we are more effective during the next disease outbreak. At least 4 discrete populations of feral swine currently exist in England at relatively low densities. In the event of a suspected classical swine fever (CSF) outbreak, investigation zones and control strategies may need to be initiated, and so new models need to be created to fit these English populations. Here, we present an approach to using data collected during scientific research projects and wildlife management exercises to aid decisions on how to resource a program of disease detection and control if CSF was suspected to have broken out in feral swine populations in England. Culling efficiency was estimated through trapping and shooting records. Results were used to create predictive models which determined resources and costs required to carry out an efficient cull within various possible scenarios. Trapping over 26 months at one 427-ha site resulted in the capture of 130 swine at an average of 0.21 swine per trap-night and US$477 per animal. Shooting by two government hunters over 12 months at another site resulted in the culling of 56 swine, equating to 1 swine shot for every 18 hrs 40 mins; total effort was 41 hrs 44 mins with total cost around US$75,628 (US$1,350) per animal. Using simulation models, we estimated the costs of delivering a cull via a combined approach of trapping and shooting to detect CSF at 1% and 5% seroprevelance. Costs ranged widely, depending on scenario, with minimum costs of US$51,404 and $69,029, and maximum costs of US$231,545 and $203,109, respectively. Results suggest that at present it is feasible to deliver a sampling strategy that could detect and potentially resolve the occurrence of CSF in feral swine in England.