1st Workshop on Wildlife Fertility Control:
What Now? What Next? Where To?

June 17 – 18, 2024
University of York
York, United Kingdom


– – Scroll down to see all available abstracts – –

1. Development of an effective, versatile humane wild hog trap

DeNicola, A.J.1, V.L. DeNicola 1,2, A. Sumrall2, P. Pontiggia2, E. Gleich3, C. Gremse4
1 White Buffalo Inc., East Haddam, CT, USA. 2 Field Engine Wildlife Research and Management, East Haddam, CT USA. 3 Bavarian State Institute of Forestry, Wildlife Ecology and Wildlife Management, Germany. 4 Brandenburg Forest Service, Dept. of Wildlife Ecology and Hunting, Germany.

Contact: Pietro Pontiggia, pietro@pontiggia.com

Wild pigs (Sus scrofa) have become a pervasive and highly destructive invasive species, causing substantial ecological and economic damage worldwide. Monitoring and control are critical in areas where pigs are invasive or there is disease risk. Trapping is a critical tool used worldwide to handle wild pigs. Traditional trapping strategies often involve traps that require substantial investment to acquire, set up and manage. These devices can educate pigs and potentially require cellular service. Given the devastating worldwide impact of wild suids, a new trapping strategy that is adaptable, efficient, and humane is needed.

We aimed to design and evaluate a trap that: 1) decreased the costs, labor, equipment, and technology required; 2) offered the ability to catch multiple groups, and 3) reduced the impacts on trapped animals. The trap design featured a double-walled net with an internal skirt, internal anchors, and external supports. This trap was commercialized in 2020 and is used successfully in more than 30 countries across five continents to address disease, research, and damage management objectives. In addition, we examined the effectiveness and ethical considerations concerning the overall well-being of trapped wild pigs.

Results have demonstrated that the trap successfully captured wild pigs while minimizing the risk of injury to captured animals. Our trap’s low-cost construction and adaptable design represents a significant advancement in invasive species management and ensures it is accessible to wildlife agencies, landowners, and conservation organizations in a variety of settings, including capture- mark- recapture studies, translocation studies, fertility control efforts, and removal projects.

2. The future delivery of oral contraceptives to control the grey squirrel (Sciurus carolinensis): do age, sex, and reproductive status affect bait uptake?

Tiberi C.1, Beatham S.2,3, Roos, D.2, Coats, J.2, Rochester, I.2, Primi R.1, Vitali A.1,Massei G.4
1Tuscia University, Viterbo, Italy. 2 Animal and Plant Health Agency, York, UK.3 Durham University, Durham, UK. 4 Botstiber Institute for Wildlife Fertility Control Europe, University of York, UK.

Contact: Cristiano Tiberi, cristiano.tiberi@unitus.it

The grey squirrel is an invasive alien species in the UK. The annual economic impact of this species is es􀆟mated at €3 million, and its presence has caused the progressive decline of the native red squirrel. Fertility control delivered through oral baits has been proposed as a method to control populations of grey squirrels. We investigated whether sex, age and reproductive status affected bait uptake in four grey squirrels’ population of Yorkshire. Squirrels were captured, fitted with a pit-tag, released, and their feeding behaviour monitored using purpose-designed bait hoppers. Hoppers were baited daily for five days with hazelnut paste mixed with the biomarker Rhodamine B. Squirrels were then recaptured and dispatched. Each squirrel was categorised based on their sex, age and reproductive status. Hair samples from each squirrel were analysed for the presence of Rhodamine B. Overall, 49% of squirrels were found positive for Rhodamine B, with more sexually active females (67%) consuming the bait than males, juveniles and non-sexually mature animals. An analysis of the PIT-tag showed that squirrel category did not strongly influence time spent feeding from hoppers. However, adult squirrels made fewer daily visits to hoppers and visited fewer hoppers per day than immature squirrels and the variability in these parameters was much greater for immature squirrels. We conclude that it is possible to deliver bait equally to squirrels of different age, sex and reproductive status, with breeding females more likely to be targeted by baits than other categories. These results could provide information on the administration of oral contraceptives and vaccines.

3. Too many wild boar: can fertility control help?

Simon Croft, S.1, Franzetti, B.2, Gill, R.3, Massei, G.4
1Animal and Plant Health Agency, York, UK. 2 Institute for Environmental Protection and Research, Rome, Italy. 3 Forest Research, Farnham, UK. 4 Botstiber Institute for Wildlife Fertility Control, University of York, UK.

Contact: Simon Croft, simon.croft@apha.gov.uk

Feral wild boar number and range are increasing worldwide in parallel with their impact on biodiversity and human activities. As traditional methods such as culling have failed to curb growth and spread, we explore whether fertility control could provide a solution. Based on empirical data from two long-term study sites we build a population model and use it to explore the efficacy of various management scenarios combining culling and/or fertility control. Our findings suggest that whilst fertility control on its own may not be sufficient to achieve target reductions in such high-density populations, adding it alongside traditional culling could halve the time to target reduction compared with culling alone. We conclude that, assuming the effort of adding fertility control to culling was found to be cost-effective in terms of population reduction, this strategy could provide a valuable, more socially acceptable tool to prevent new and mitigate existing human-wild boar conflicts.

5. Assessing the short-term impact of DiazaCon treatment on fertility indicators in grey squirrels

Pinkham, R.1, Mackenzie, G. 2,3,  Entract, G.2,3,  Corbitt, T.2, Massei, G.4,
1 Animal and Plant Health Agency, York, UK. 2 Sporomex Ltd, UK., 3 University of Hull, Hull, UK, 4 Botstiber Institute for Wildlife Fertility Control, University of York, UK.

Contact: Rebecca Pinkham, rebecca.pinkham@apha.gov.uk

Background. The impact of non-native invasive grey squirrels (Sciurus carolinensis) in the UK could be mitigated by reducing their numbers through oral contraceptives. One potential target for contraceptives is cholesterol which is a precursor for reproductive hormones. Reducing normal cholesterol levels by over 40% can induce infertility. We tested the contraceptive effect of a cholesterol mimic, DiazaCon, which acts by preventing the production of reproductive
hormones in both birds and mammals.

Methods. We mixed DiazaCon into a free-feeding bait given to captive male grey squirrels and monitored testosterone and cholesterol levels in treated and control animals. Results. We observed lower levels of testosterone in squirrels given DiazaCon, however there was high variation of hormone levels in both groups and a clear avoidance of DiazaCon-treated bait compared to control bait. To increase palatability of DiazaCon-treated bait, we explored taste masking of DiazaCon using Sporopollenin Exine Capsules (SpECs, Sporomex Ltd.), shellac, maize starch, and cocoa butter. Combinations of masking additives increased bait uptake compared to DiazaCon alone and produced an overall reduction in cholesterol, and in some animals reaching the 40% target level required for expected infertility at between fourand eight-weeks post-treatment.

Conclusions. DiazaCon-treated bait was unpalatable to squirrels, leading to insufficient uptake to affect fertility. However, the reduction of cholesterol in treated squirrels that did take bait suggests that DiazaCon could have a short-term contraceptive effect if palatability issues could be overcome. Further improvements concerning taste and odour masking are required to achieve effective uptake levels

7. Grey squirrels Sciurus carolinensis and the spread of tick-borne diseases: how does fertility control compare to traditional culling?

August, K.1, Belmain, S.1, Bray, D.1, Massei, G.2, Birtles, R.3, Marshall, H.4, Croft, S.5, Beatham, S.5, Broadhurst, H.3
1 University of Greenwich, London, UK. 2 Botstiber Institute for Wildlife Fertility Control, University of York, UK. 3 University of Salford, Salford, UK. 4 Forest Research, Edinburgh, UK. 5 Animal and Plant Health Agency, York, UK.

Contact: Katherine August, Katie.August@greenwich.ac.uk

The grey squirrel Sciurus carolinensis is an invasive species in the UK, with detrimental impacts on trees and the conservation of native wildlife. Additionally, grey squirrels may carry the tick-borne bacterium Borrelia burgdorferi, which causes Lyme disease, a growing public health risk in the UK. As such, intense efforts are carried out in an attempt to control grey squirrel populations, and some experts argue that this may reduce the incidence of Lyme disease. Grey squirrel control traditionally involves culling through trapping or shoo􀆟ng; however, fertility control is being explored as an alternative. This project aims to 1. Quantify the importance of grey squirrels in the ecologies and transmission of ticks and Borrelia burgdorferi; 2. Compare the impact of grey squirrel control through culling and fertility control on 􀆟ck abundance and Lyme disease risk; and 3. Develop new tools for tick monitoring, surveillance and control. In the absence of oral contraceptives, we will mimic the results of fertility control by only removing juveniles. Using fourteen small (8-15 ha each), isolated woodlands in South Cumbria, we will assess grey squirrel and tick densities before and after each treatment: no culling (n = 6), culling (n = 4) and fertility control mimic cull (n = 4). Ticks will be tested for pathogen presence and blood meal analysis performed to assess the wildlife species being fed upon. The results of this study will elucidate the capacity of population control methods to reduce grey squirrel numbers and provide recommendations to limit the spread of ticks and their pathogens.

8. Grey squirrel impacts on biodiversity and ecosystem services in UK woodland habitats

Frost, M.1, White, P.1, Maskell, L.2, Massei, G.1, Haw, K.3,  Isted, R.4
1 Department of Environment & Geography, University of York, UK. 2 UK Centre for Ecology & Hydrology, Lancaster Environment Centre, UK. 3 UK Squirrel Accord, c/o RSST, London, UK. 4 Forestry Commission England, Bristol, UK

Contact: Molly Frost, lzr507@york.ac.uk

UK Government targets for carbon reduction and nature recovery include significant expansion of woodland. Non-native grey squirrels pose a major threat to these ambitions. Grey squirrels have successfully colonised much of the UK and have contributed to the decline of the native red squirrel. Bark stripping by grey squirrels reduces the economic value of tree products and increases the susceptibility of trees to pests and disease. It is likely that grey squirrels have other impacts on biodiversity and ecosystem services that have yet to be explored. This research is undertaking a systema􀆟c approach to investigating the impacts of grey squirrels on biodiversity and ecosystem services. This is a necessary area of focus to support Government policy on woodland expansion, as well as providing further evidence to strengthen policy on grey squirrel management. Research outputs will contribute to national strategic planning for both red squirrel conservation and grey squirrel management which aim to promote community support and involvement. The Common International Classification of Ecosystem Services (CICES) has been used as a framework for mapping out potential links between grey squirrel activities and their impact on ecosystem services and biodiversity. We present system maps summarising the available evidence and highlighting priority knowledge gaps, which will be addressed in the next stages of the research. Future work will model the benefits of grey squirrel management for the selected biodiversity and ecosystem services, including consideration of both traditional and emerging methods, such as culling, predator introduction and fertility control.

11. Evaluating safety and effectiveness of a single dose immunocontraceptive vaccine for fertility control in the invasive alien species coypu (Myocastor coypus)

Cotti, C.1,  Delogu, M.1,  Spinaci, M.1,  Govoni, N.1, De Santis, F.1, Pinkham, R.2, G. Massei3
1Department of Veterinary Medical Sciences, University of Bologna, Ozzano Emilia (BO), Italy; 2Animal and Plant Health Agency, York, UK. 3 Botstiber Institute for Wildlife Fertility Control, University of York, UK.

Contact: Claudia Cotti, claudia.cotti@unibo.it

The coypu (Myocastor coypus) is an aquatic rodent native to South America which was imported for fur farming into Europe, Asia, Africa and North America. In these areas, the coypu has a significant negative impact on biological diversity, ecosystems, crops and irrigation systems. In order to mitigate these impacts and to test an alternative to culling, we proposed a European Union-LIFE project (LIFEGREEN4BLUE) aiming to carry out a pilot trial to evaluate the short-term effectiveness of a single dose of the immunocontraceptive GonaCon (USDA-APHIS Wildlife Services) in captive coypu. In 2023, 8 sexually mature female and 2 male coypus were housed in purpose-built pens, and after a period of acclimatization, animals were assigned to Treatment and Control groups. On February 1st, 2024, treatment females were administered with a 1 mL single dose of GonaCon, whilst Control animals received the same dose of a saline solution. No differences in behaviour and adverse injection site reaction have been observed between vaccinated and untreated coypu so far. Forty-five days after vaccination females of both Treatment and Control groups will be housed with nonvaccinated males. Blood was collected at vaccination and will be collected every month for 8 months following vaccination. The effect of GonaConTM will be assessed by measuring anti-GnRH antibody titres, hormone profiles (progesterone and testosterone) and by ultrasound scans of the females to detect pregnancies. These data will provide the baseline for future field applications of fertility control to reduce the number of coypu.

14. Fertility control in rodents provides ecological balance and improves animal welfare of the food chain.

Mayer, L.1, Shuster, S.2, Dyer, C.1
1 Wisdom Good Works, Flagstaff, AZ, 2 Northern Arizona University, Flagstaff, AZ

Contact: Loretta Mayer, lmayer@wisdomgoodworks.org

The lethal approach to rodent control has been the most common method for pest management in human populations. Clearly, after centuries applying this strategy, we have enough data to conclude lethal approaches, particularly poison, is not sustainable. Fertility control, on the other hand, has not been extensively investigated. The literature in this area is growing and new strategies are emerging. We believe that the barriers to fertility control for invasive rodents are: poor public awareness of this method and of the effects of rodenticides on rodent welfare and the food chain, difficult to demonstrate success in a model where the “absence” of an observation is the goal, and solutions that to date are too costly and therefore impractical. We have formulated an organic plant-based rodent feed that is nutritional, and costs less than poison, and is effective at blocking fertility in a contraceptive manner. We have conducted trials feeding Norway Rats (Rattus norvegicus), Black Rats (Rattus Rattus), and House mice (Mus domesticus). These trials have been conducted in “open” and “closed” field populations. In all settings, rodent populations (utilizing a population index of consumption and camera trapping) declined by 98% (closed) and 60% (open) in 5 months. The aim of using this contraceptive will be to achieve a reduced number of rodents that can be consumed without effects on predators and scavengers. We are currently collecting individual rodent DNA samples to investigate markers for immune system improvement and poison resistance. We believe the benefits of fertility control by feeding a natural contraceptive can improve human-animal conflicts.

15. Immunocontraception and Human Elephant Conflict Another Tool in the Conflict Mitigation Toolkit.

Delsink, A.1, Bertschinger, H.2, van Altena, JJ1.3, Schulman, M.2, Cryer, P.4, Bindumadhav, S.5
1 Humane Society International/Africa, Cape Town, Republic of South Africa. 2 University of Pretoria, Section of Reproduction, Onderstepoort, Tshwane, Republic of South Africa. 3 Global Supplies, Gauteng, Republic of South Africa. 4 Bio-Diversity Conservation Foundation, Salt Rock, Kwa-Zulu Natal, Republic of South Africa. 5 Humane Society International/India, Bangalore, Karnataka, India

Contact: Audrey Delsink, adelsink@hsi.org

For >25 years, the native porcine zona pellucida (pZP) vaccine has been successfully used for immunocontraception of wild horses, white-tailed deer, wild African elephants, and approximately 100 other species in zoos. In South Africa, about a third of the country’s elephants occur in fenced reserves, under management of multiple stakeholders with diverse land uses. In 1996, an international team established proof of concept and contraceptive efficacy in African elephants in Kruger National Park (KNP). A field study to test population and behavioural effects of pZP on cows in the Greater Makalali Private Game Reserve (GMPGR) was initiated (2000). Subsequently, pZP was administered in approximately 50 reserves with populations ranging from 95%. Safety and lack of impact on social behaviour were demonstrated. pZP fertility control is a management tool that reduces and stabilizes local population growth rates in the medium to long-term. Thus, competition for local resources, particularly amongst bulls who may seek out new ranges outside perimeter fences due to high local population growth, is achieved, contributing to human elephant conflict mitigation in the long-term. An emerging context is the potential management of Asian elephants with pZP.

16. Community Support for the Use of Rodent Fertility Control in Washington DC

Gerberich, H., University of Exeter, Exeter, UK

Contact: Holly Gerberich, hg507@exeter.ac.uk

Urban rodent control is an ongoing challenge in Washington DC, one of the top five ‘rattiest cities’ for the past eight years. Lethal methods of abatement have fallen short, and social appetite for poison and killing rats (rattus norvegicus) is diminishing. The swell of research on the potential of fertility control as a more humane and effective approach to managing rodent populations is promising, but such a novel tool requires both community support and political will. This research explores Washingtonians’ attitudes towards rats in DC and their appetite for testing rodent fertility control. Overwhelmingly, focus group participants in this study responded in favor out of a profound mix of frustration and helplessness as a result of their personal struggles with rats and reticence to kill them. Conversations with DC Health officials to convey this sentiment revealed several obstacles to employing rodent fertility control, namely an inconclusive pilot study using ContraPest® (Senestech). The experience soured officials’ willingness to explore the use of a chemosterilant any further. Other problems include a lack of sufficient metrics to define and measure success, questions around the uptake speed of the bait, the amount of bait needed to sustain goal numbers, and a lack of practical ways to count individual rats. Given the widespread resident support, DC Health is encouraged to repeat the ContraPest® field study in a way that is methodical, iterative, and replicable to determine if wider application is merited. A recommended framework is outlined for consideration.

17. Working With Communities In The United States To Reduce Suburban Deer Populations Using Pzp Immunocontraception:  Strategies For Success

Rutberg, A.1, and Pereira, K.1
1Center for Animals and Public Policy, Cummings School of Veterinary Medicine at Tufts University, North Grafton, Massachusetts, USA

Contact: Allen Rutberg, allen.rutberg@tufts.edu

After more than 35 years of research on wild and captive horses, deer, elephants, and dozens of species of zoo animals, the safety and effectiveness of porcine zona pellucida (PZP) vaccine as a remotely deliverable wildlife contraceptive has been definitively established. More challenging, however, has been demonstrating that PZP or any contraceptive can be used to stabilize or reduce free-roaming wildlife populations in situations of intense human-wildlife conflict. Non-lethal reduction of wildlife populations using porcine zona pellucida (PZP) vaccines has been achieved in wild horses, deer, and other species in a variety of physical, social, and political environments across the United States.   We draw several important lessons from three decades of population research on white-tailed deer (Odocoileus virginianus) using native PZP (registered as ZonaStat-D with the U.S. EPA) and the longer-acting PZP-22 in different environments.  Successful projects require  (1) a committed and patient implementation team; (2) a wide base of supporters and strong partnerships with local authorities and landowners; (3) significant time and resources invested in learning about the behavior, demographics, and accessibility of the local deer population; (4) commitment by partners to long-term allocation of resources; (5) informing and engaging the public; (6) specifying goals, measuring outcomes, and re-evaluating; and (7) incorporating immunocontraception into a comprehensive plan for addressing local conflicts related to wildlife abundance.  As an ethical imperative, any application of fertility control to wildlife should minimize harm to and respect the wild lives of the treated population.