I have been considering non-lethal deer (ungulate) management methods in urban and semi-urban areas.
While in most places the overabundance of deer is related to land management practices (clear-cuts, the elongation of forest edges due to forest fragmentation, intensive agriculture etc.) as well as lack of large predators, there is still the issue of regulating deer numbers near settlements where large predators normally do not live (due to human disturbance) even if they have recolonized the region, and where horticulture, orchards etc. are also present abundant resources to the deer that can increase deer numbers.
In such areas, culling is controversial and in some places it is even impossible due to safety reasons.
Personally, I am against deer culling in general.
From what I understand of deer social and reproductive behaviour, culling can actually lead to a denser deer population at least in red deer species (e.g., Coulson, T. et al., 2004).
This has been especially observed, for example, following the demographic and density patterns in red deer on the Isle of Rum where release from hunting led to the females becoming the dominating group which, through, direct and indirect mechanisms increased calf mortality; increased the female deer age to her first reproduction; increased emigration rates due to dispersal; and generally lowered the red deer population density.
In fact, the Isle of Rum researchers even suggested that in order to have more deer to harvest, female deer should be culled (Pemberton, J. & Kruuk, L., 2020).
While my objective is not one of attempting to benefit human hunters, this serves as evidence that deer inherent social and biological mechanisms lead to decreased density until ecological capacity is reached and, through hunting, these mechanisms are disrupted.
In relatively natural communities release from hunting might apparently lead to population increase during the first decade and then to gradual stabilization over approximately 30 years.
I have not encountered much information regarding such processes in roe deer who are different in both their reproductive and social organization.
I have been considering alternative methods to culling that might work in areas which are close to human settlements and which deer (ungulates) sometimes use as shields against predators.
Specifically, I have been considering urban and semi-urban areas.
On one hand, I have been reading about immune-contraceptives such as PZP which are non-hormonal and therefore less intrusive on the wild species behaviour.
They are also reversible meaning that the females do not lose their fertility and they can have a chance at reproducing later or sporadically during their lifetime.
On the other hand, I was wondering about a more novel approach which I would like to discuss.
My idea concerns ‘deer herding’.
There are several natural regulatory forces controlling ungulate populations: food abundance (which affects territory/home range size), mortality (due to predation by carnivores or due to inclement weather, disease, road accidents etc.), social mechanisms etc.
I have been wondering about combining food abundance (dispersing high-quality resources far enough in order for the animals to maintain larger home ranges which reduces their density) and a certain aspect of predator effects, namely, creating the ‘landscape of fear’ which, on this occasion, would translate into ‘landscape of disturbance’ or, if you may, nuisance 🙂
While large predators do not live in urban, semi-urban, peri-urban areas (which is why some ungulates who are more tolerant to human disturbance tend to settle closer to humans in order to escape predator pressure), the landscape of fear could be mimicked by certain ‘herding’ activities that would be carried out by employed (or volunteer) humans.
It might be possible to assess the area which needs to be managed by identifying zones where the deer are allowed to graze/browse and to move freely (their actual resources) and where their activities should be reduced.
In areas where natural resources of optimal quality are very scarce (if deer do not have access to optimal food resources, they will attempt to maintain their body condition by, for example, tolerating disturbance in order to be able to feed on suboptimal resources), these could be supplemented by creating wildlife grazing meadows with grasses, forbs, shrubs and brambles (see, e.g., Genghini, M. & Capizzi, D., 2005).
These could be the officially designed optimal quality deer areas and they should be patchy enough for the herd / individual to travel longer distances between them (to maintain larger territories).
These patches should also be connected by semiwild or wild corridors in a manner that disallows the deer to stray significantly from the predesignated path which could lead to crossing ‘areas of temptation’ such as orchards or fodder fields.
Meanwhile, areas that should not be receiving grazing pressure and that cannot be fenced due to some reasons (e.g., they are too extensive or they form a public-access park/area which cannot be closed) but that are in need of protection (e.g., parks), could be managed by hiring ‘deer herders’ who would routinely walk the area (perhaps with non-aggressive but barking dogs) to chase the deer away and to create sufficient disturbance for the deer not to prefer to visit these areas or to linger there.
This herding could be done every day during crepuscular hours and perhaps at night, as well, visiting the sites that the deer should not feel ‘as welcomed’ at and scaring the deer away from them.
Of course – while routinely – it should not be done following the same route, at the same times every day, otherwise the deer would simply habituate and learn the patterns of ‘herding’ attendance.
This method might be particularly applicable to large public parks which have their wilderness areas but which also have their areas that should be protected from large herbivore impact.
The ‘herders’ should not harm the deer.
The aim would be to cause enough disturbance (nuisance) for the deer to begin picking the ‘more peaceful’, optimal sites that are officially designated for their use.
(It is, however, important to remember that deer also need shelter and breeding sites as well as suitable areas while the females are moving around with their less mobile young.
If only foraging needs were taken into account, deer might still visit unwanted areas if those were the exclusive sites to provide other types of resources sought for daily or during specific life stages.)
Another benefit of deer herding might be the increased rate of movement and potential degrouping.
In many places, slight herbivory does not cause much damage but usually the problem is related to heavy grazing for prolonged periods of time (just like livestock grazing can improve the quality and biodiversity of semiwild habitats if it is not intensive and if it is extensive, rotational etc.).
In fact, predator fear effect ensures precisely this – the deer form smaller herds, they move around more, they stay in one place for less time etc.
This (if not overdone) could additionally improve deer fitness by reducing disease transmission rates and also by reducing fat accumulation rates which, for example, in red deer (as capital breeders) can lead to increased birth rates (although probably not in roe deer who are income breeders).
The birth rates might be lower if the female deer were less sedentary, more active and could not obtain their bulk forage in one patch.
Mobility and reduced opportunity to form large groups in abundant grazing/browsing areas can reduce disease rates in ungulates which might lower the burden of infections both within the wild population and between the wild population and domestic animals.
This might be a curious strategy to consider. It would make for an interesting project in some large public park or another area where deer can visit some places but should be kept out from others and where it is very difficult to establish these boundaries with fences and other physical obstructions.
Additionally, vegetation like brambles, forbs, flowering shrubs that might be introduced to attract deer to their optimal grazing/browsing grounds, is highly beneficial for many other species and could improve biodiversity in the area (so could natural migration corridors).
Large predators cannot solve all of our problems because they are less tolerant of human disturbance than many ungulates (especially, roe deer) and therefore there will always be areas where large predators do not hunt but where deer persist (perhaps even precisely due to the lack of large predators) and where we have to come up with alternative management methods.
Killing the deer is the ‘easiest’ option but it might be even counter-productive as demonstrated by research in wilder ecosystems.
Fences and high hedges cannot work in all places although they are effective.
‘Deer herding’ is a non-lethal method for mixed, complex areas and could possibly create jobs.
Notes by Ieva 