Predation control through the induction of conditioned prey aversion could be used as an alternative to predator control to reduce predatory pressure on nests of partridges or other threatened ground-nesting birds.
La predation It is a type of ecological interaction in which one animal – the predator – hunts another animal of a different species – the prey – to feed on it. This biological relationship is one of the causes of historical conflict between man and certain wild predators, which are perceived as a threat to the use of game species and/or livestock. Furthermore, predation can be a determining factor of reproductive success and conservation status of some prey species, especially in the case of those whose populations are already in decline for other reasons, generally of anthropic origin.
The predation exerted by the fox (Vulpes vulpes) on the sunsets red-legged partridge (Alectoris rufa) is a good example of a somewhat conflictual predator-prey relationship. Historically, the fox has been considered a threat to the hunter's interests as it is a prominent predator of partridges. For her part, the queen of small game hunting in Spain has suffered a significant population decline in recent decades due to multiple factors, especially the intensification of agriculture. In this situation, increased predatory pressure by the fox, which can become relatively abundant under certain circumstances, can influence the abundance and population dynamics of the partridge, aggravating its population decline.
The fox is an outstanding predator of partridge eggs and chicks, being able to influence its abundance and population dynamics and generate a human-wildlife conflict as it is seen as a threat to partridge hunting.
Currently, the resolution of this type of conflict goes through the so-called "predator control”, a hunting management practice that consists of reducing the populations of certain opportunistic predators, such as the fox, to avoid excessive abundance. However, it is a relatively expensive practice, it means the death of predators, it has negative effects on ecosystems, the effectiveness and selectivity of the legal methods used are not always the desired ones, and sometimes illegal methods are resorted to. control, such as the use of poison, to achieve the desired end. In this way, it seems recommendable to work on the development of new tools aimed at reducing conflicts derived from predation.
The control of predators supposes the death of the controlled species by means of expensive methods and of reduced selectivity in occasions, being necessary the development of more effective, sustainable and ethical tools.
In this sense, the predation control by induction of conditioned aversion (CA) to prey could be a valuable alternative to predator control. The AC consists of using chemicals on the prey (or an imitation of it) that produce an unpleasant adverse effect –such as vomiting, nausea and/or diarrhea– on the predator, so that it learns to reject this prey in subsequent encounters. It is about triggering a survival mechanism that many animals develop to avoid the consumption of toxic or spoiled food once they have had a first bad experience.
Conditioned aversion (AC) to the prey can be used for the fox to reduce its appetite for partridges, or for the wolf (Canis lupus) hates feeding on domestic livestock, reducing human-wildlife conflict with these predatory species.
Members of the Wildlife Toxicology Group and the Game Resources and Wildlife Management Group of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM) have advanced in the development of this non-lethal tool for predation control.
For 2 years, a total of 26 foxes were captured and tagged with GPS transmitters in 2 hunting boundaries, in which a treatment area for the application of the CA and other control zone, that is, without AC application. Just before the galliforme laying period, they placed partridge artificial nests in the areas of maximum use of the marked foxes, and these were monitored with camera traps. In the treatment areas of both bounded, the artificial nests contained eggs with the aversive substance, a chemical compound of low toxicity selected from previous studies with dogs in captivity.
Capture for radiolabeling and subsequent release of one of the foxes participating in the research work.
After 3 weeks, new partridge nests were placed in the treatment and control areas, but this time without the aversive chemical, in order to check whether the foxes in the treatment areas had acquired an aversion towards them. Throughout all this time and simultaneously, Partridge productivity and density were estimated before and after CA treatment in both areas., in order to verify the real effect of this predation control method on the partridge population.
One of the radio-tagged foxes is detected by a camera-trap preying on a partridge nest.
The results show that CA can stop predation of partridge nests in 78% of conditioned foxes for an entire breeding season, and temporarily (for 20-46 days) in all other conditioned foxes. The partridge population responded positively to this reduction in the level of predation, increasing their productivity between 132 and 677% compared to the control areas in which CA was not applied. This increase in productivity caused the density of partridges to increase much more –between 193 and 292%– in the treatment areas than in the control areas.
This research work shows that it is possible to generate CA in wild canids, and it can be used as a non-lethal hunting management tool or conservation to reduce predatory pressure on nests of partridges or other birds, improving the cost-effectiveness of the objective pursued with predator control. In addition, it opens the door to the potential use of this technique to alleviate the human-wildlife conflict derived from wolf predation (Canis lupus) on domestic livestock, or the conservation of some endangered birds that nest on the ground such as capercaillie, bustard or little bustard. The use of this method can also contribute to reduce predator control measures and, especially, the use of illegal control methods, such as poison, which seriously affect species of carnivores and protected birds of prey and scavengers.
The scientific publication of this research is available at:
- Tobajas, J., Barefoot, E., Mateo, R., Ferreras, P. 2020. Reducing nest predation of ground-nesting birds through conditioned food aversion. Biological Conservation 242, 108405.