In many cities around the world, there are wild animal species whose presence is enjoyed by some and a nuisance to others. Management of such species should be informed by economic analysis as well as ecological, ethical and animal welfare considerations.

I had better say this right away: this post was prompted not by the current Covid-19 pandemic, but by repeated sightings last summer of a fox around my London home.  Nevertheless, the pandemic does show that the proximity of wild animals can in certain circumstances have enormous adverse consequences for humans.  At the time of writing, the precise source of the initial outbreak in Wuhan, China, is not known, but it appears that the virus was transmitted from wild animals to humans at a market.  Quite possibly, however, it was a wild animal farmed outside the city and brought to market for sale, and not therefore urban wildlife in the sense considered in this post. 

Human attitudes to wildlife depend greatly on its nature, location and behaviour.  Large carnivores in what remains of their natural habitats are widely considered worthy of conservation efforts, but if such a creature should be on the loose in a city, as happens occasionally (1), then most people would  support its killing in the interests of public safety if other options are impractical or ineffective.  Very small animals encountered in or near people’s homes may evoke little affection or sympathy: many who would never harm larger animals will happily swat a fly or lay a mouse trap. 

Between these extremes are medium-sized wild animals present in and adapted to life in cities about which people may have differing or complex attitudes – animals not large or dangerous enough to present a major physical risk to human life, but capable of being a considerable nuisance while also evoking human sympathy and the protection of custom or law.  Table 1 below lists some examples (this has been compiled from numerous online sources which it would be tedious to list in full).

Trying to be objective, I have avoided any reference to animals “attacking” humans, as it is apparent that what one source considers an attack, another may view as defensive action in response to human provocation or to protect young.  In the same spirit, I have not stated that any of the animals “spread” human diseases.  Undoubtedly many urban wild animals carry pathogens that are potentially harmful to humans (2).  The questions then are the likelihood of transmission to humans, and whether transmission can be prevented by simple precautions such as washing hands after contact or requires more elaborate preventive measures.  It is also pertinent to consider whether or not the risks to humans are greater than those already encountered from pets and domestic animals.

There seems to be little literature on the application of economics to the management of such urban wildlife.  What literature there is on the economics of wildlife management focuses mainly on rural wildlife, as is apparent from the highlighting of costs from harm to livestock and crops, and benefits from hunting and recreation (11).  Nevertheless, the insight that there may exist an optimum population size which maximises benefits less costs (12) appears relevant to urban as well as rural wildlife.

Before pursuing this argument, I will briefly address some lines of thought that seem unlikely to be helpful in informing management strategies for species of the sort listed in the table.  Firstly, conservation is not normally an issue for such species.  It may be that their adaptation to urban environments is to some extent a response to loss of their natural habitats.  But all the listed species are classified by the International Union for the Conservation of Nature as of least concern (13), implying that their populations are large enough that they are far from any risk of extinction.  Secondly, and as a consequence of the above, a focus on such species’ contribution to biodiversity, and on the economic value of that contribution, is unlikely to yield useful information.  There is no foreseeable risk that that contribution will be lost.

Any attempt to measure the benefits and costs to humans of an urban wildlife species would require application of a judicious selection of non-market environmental valuation techniques.  Benefits from observing animals might be measured by adapting the travel cost method, typically used in valuing parks and other recreational sites, to allow for the fact that the animals are not concentrated at one site but spread out across an urban environment.  Thus the relevant travel costs are not those incurred in getting to a particular site but those incurred in getting to wherever, at a particular time, an animal can conveniently be observed.  The “travel” required to make such an observation when at home might be no more than getting up and coming to a window when alerted to an animal’s presence by a family member.  The fact that such “travel” may involve very little cost – the value of perhaps just a minute or two of a person’s time – does not mean that the benefit is correspondingly low.  This is because the travel cost method measures value in terms of consumer surplus – in simple terms the difference between the cost a person would have been willing to incur to view an animal and the cost they actually incur.  The cost they would have been willing to incur might be assessed from the costs actually incurred to view an animal by other people who happen to live where such animals are not present.

Benefits from controlling species regarded as harmful might be measured using a combination of ecological and economic analysis.  Ecological analysis would attempt to quantify the effect of the population of the beneficial species on the population of the harmful species, and the relation between the population of the harmful species and specific forms of harm (theft of unprotected food, dispersion of pathogens, dropping of faeces, chewing of materials, etc).  It would then be for suitable economic analysis to attempt to value the benefit from a reduction in the relevant forms of harm.

The costs attributable to urban wildlife include numerous components.  Theft of food that would otherwise have been available for human consumption can as a minimum be costed at its market value or, where prepared at home from bought-in ingredients, at the market value of the ingredients plus the opportunity cost of the preparation time.  The cost of overturned bins might be taken to be the opportunity cost of the time spent in cleaning up, and that of disturbance to gardens and damage to buildings the cost of reinstatement or repair.  In the case of damage to overhead power lines, the cost of the power outage should be added to the repair costs.  Power outage costs will depend on how many users are affected and what they use electricity for, but can be very large (14).  The cost of injury or ill-health attributable to urban animals should include the costs of associated healthcare and of lost income (to employees) or lost production (to employers) due to time off work.  Given suitable information about the effect of education on children’s employment and earnings prospects, one might also include a cost element for time off school.  Estimating the costs of ill-health of retired people raises issues beyond the scope of this post (15).

Where nuisance attributable to animals is recurrent, further costs may arise. Various forms of avertive behaviour may be adopted in an effort to minimise the nuisance.  These may include: never eating out of doors; keeping windows closed (even in hot weather); buying larger or more secure waste bins; fitting spikes where birds might want to perch; setting deterrents  such as motion-sensitive lights, chemical sprays and imitation snakes; and going out of one’s way to avoid certain locations.  All these have costs: either direct monetary outlays, or time costs, or costs of restrictions on life-style. The last-named costs might be estimated using the hedonic property method, requiring comparison of house prices in locations with and without the need for such restrictions.

None of this is easy.  Even an apparently simple case such as theft of purchased food  requires reliable data on the quantities and types of stolen items, and the species responsible for theft.  Although the economics of environmental valuation has made great strides in recent decades, its application to the full range of benefits and costs of particular species, and collection of the necessary data, would present enormous challenges.

It is plausible to suppose that a higher urban population density of a wild species will not imply proportionately higher benefits to humans.  The principle of diminishing marginal utility suggests that someone who enjoys seeing a fox or a monkey is unlikely to obtain ten times as much enjoyment from seeing ten foxes or monkeys, or from seeing just one ten times as often.  That could be tested empirically by observing how much time and effort a person incurs to view such animals, and how that time and effort varies with the number of known opportunities for views.   

The costs to humans of a higher urban population density of a wild species, however, may be more than proportionately higher.  One overturned waste bin in a street may be seen as an exception. Many such bins not only create proportionately more clean-up work, but may also be perceived as lowering the tone of the neighbourhood, and may prompt efforts to address the problem by deterrent measures or obtaining more animal-proof bins. Occasional animal noises may be a minor issue, but persistent noise, especially at night when it may disturb sleep, can be a serious problem.  Similarly, occasional theft of food may be tolerable, but routine thieving may force changes in life-style, such as never eating out of doors, keeping windows closed even in hot weather, and abandoning businesses selling food at outdoor market stalls.

If these suggestions are broadly correct, then we can represent the situation in terms of the sort of diagram familiar from, for example, the economics of pollution control.

As in other contexts, net benefit is maximised when marginal benefit equals marginal cost.

However, such an approach should not be the sole determinant of how a species should be managed.  It is also important to consider, from the perspectives of effectiveness, cost and ethics, the means of getting from the current to the optimum population.  More fundamentally, an animal rights perspective would suggest that an approach based solely on benefits and costs for humans is to be rejected as an example of human supremacism (16). 

What would be missing, in an approach that only takes account of benefits and costs for humans, is consideration of animal welfare.  That implies, as a minimum, avoidance of direct cruelty to animals including, in particular, avoidance of practices such as blocking of dens and use of poisons that subject animals to lingering and unnecessarily painful deaths.  The importance of animal welfare in this narrow sense is widely recognised: in the UK, for example, use of such practices to kill foxes is illegal (17).

However, appropriate management of urban wildlife requires a much broader conception of animal welfare that has regard to the extent to which animals lead worthwhile lives with a positive balance of well-being over suffering, and to how humans and the urban environment they create can affect that balance.  Positive features of an urban habitat may include a plentiful food supply and an absence of natural predators.  Negative features may include intense competition for territory and the risk of death or injury in road accidents.  The balance might be expected to vary between species and locations.  

Ideally, management of an urban species should be informed by knowledge not only of the actual welfare of its members but also of how their welfare might change if its population density were to increase or reduce, or if features of its environment were to change.  But rarely if ever do we have such knowledge (18).  Even our knowledge of actual welfare is very limited. 

There is a further difficult and contentious issue.  Philosophers have explored, in respect of humans, the ethics of policies that affect the size of the future population.  How should we choose between scenarios A and B, if people in A have greater well-being but people in B are more numerous?  Totalism asserts that we should maximise total well-being, calculated as population multiplied by average quality of life (19).  Averagism holds that we should maximise average quality of life, without regard to size of population.  Both these positions, and others, have been shown to have counter-intuitive implications.  A considerable literature in this field has not led to anything approaching a consensus.  The point here is this: the same ethical issue arises in respect of actions or policies which affect the size of an animal population. 

A plausible assumption is that the average well-being of an animal species is greatest when its population density is neither too small nor too large.  If it is too small, then it may be very difficult for individuals to learn behaviour from others or to find mates.  If it is too large, then competition for territory may become severe, diseases may spread more easily, and the available food supply may be inadequate.  Rather more speculatively, it might be argued that if population expands beyond the level that its food supply can support, then average well-being will decline so rapidly as to render the debate between totalism and averagism irrelevant (because total welfare will fall despite the extra population).  If so, then the relation between population density and welfare, according to whatever is our preferred measure of overall welfare of an animal population, could be represented as in the diagram below.

There is still much that this analysis leaves out.  It passes over the issue of what in an animal’s environment we are regarding as held constant as its population density varies.  Whatever management method might be chosen – for example shooting, poisoning or sterilization for a reduction in population, and providing extra food or nesting opportunities for an increase – would in itself amount to a change in the environment.  It also omits the ecological consequences of a change in the population density of an animal species.  Through food chains and in other ways, there are likely to be effects on the populations of other animal species, and so in turn on the welfare of those species.

Nevertheless, it is I believe of interest to consider the implications of putting together the economic analysis summarised in Diagram 1 and the animal welfare analysis summarised in Diagram 2.  I assert the following:

Proposition 1: There is no reason to suppose that the population density of an urban animal species that optimises its net benefit to humans is the same as, or even close to, the population density that optimises its own overall welfare.

The justification for Proposition 1 is simply that the bases of the optimum for humans and the optimum for the animal species are entirely different.  It would be entirely coincidental if these optima happened to be the same or close. 

For the next proposition it is convenient to represent the actual current population density of an urban animal species in a particular location as A, its optimum density for humans as O_H, and its optimum density for animal welfare as O_A.  We can then state:

Proposition 2:  For any urban animal species, there are 6 possible orderings by increasing animal population density of A, O_H and O_A.  For 4 of these orderings, there is available what might be termed a Pareto improvement (20), a change in population density that would yield a net benefit for humans and raise the overall welfare of the animal species.  For the other 2 orderings, a change in animal population density that was advantageous to humans would be disadvantageous to the animal species, and vice versa.

The 6 possible orderings are: 1) A < O_A < O_H ; 2) A < O_H < O_A  ; 3) O_A < O_H < A ; 4) O_H < O_A < A ; 5) O_A < A < O_H ; 6) O_H < A < O_A .

For ordering 1, an increase in population density from A to O_A would optimise the overall welfare of the animal species, but also bring the net benefit for humans closer to that at O_H.  For ordering 2, an increase from A to O_H would optimise for humans but also raise overall welfare for the animal species.  For orderings 3 and 4, a suitable reduction in population density would be beneficial for both humans and the animal species.  It is only for orderings 5 and 6, in which A is between O_A and O_H, that a change in density can be beneficial for humans or for the animal species, but not for both.

Proposition 2 should not be taken to imply that the 6 orderings are equally likely: such a claim would be way beyond what can be supported by current knowledge.  What it does suggest, however, is that, in the management of an urban animal species there is not necessarily a conflict between what is good for humans and what is good for the species.  Where an urban animal species is, on balance, a nuisance to humans, it is possible that a reduction in its population would also be good for the species. 

However, that is just a possibility.  It is also possible that a reduction in the population of an urban animal species would be good for humans but bad for the species.  Much more research is needed to enable us to make well-supported decisions on the management of urban animals.

Notes & References

1. The Guardian (29/9/2016) Lion shot dead at Leipzig zoo after escaping from enclosure https://www.theguardian.com/world/2016/sep/29/two-lions-escape-from-leipzig-zoo-enclosure
2. “Pathogen” is a general term for micro-organisms that can cause disease, including viruses, bacteria, fungi, protozoa and worms.
3. Metro (8/9/2018)  Inside the secret world of London’s urban foxes  https://metro.co.uk/2018/09/08/inside-the-secret-world-of-londons-urban-foxes-7923273/
4. Aberdeen City Council  Living with Urban Gulls  https://www.aberdeencity.gov.uk/sites/default/files/2018-05/Living%20with%20Urban%20Gulls.pdf
5. Reuters (11/12/2018)  Monkeys run amok in India’s corridors of power  https://uk.reuters.com/article/us-india-monkeys/monkeys-run-amok-in-indias-corridors-of-power-idUKKBN1OA01R
6. East Coast Radio (30/8/2017) Monkey-ing around – harmless or menace?  https://www.ecr.co.za/shows/terence-pillay-iinvestigates/monkey-ing-around-harmless-or-menace/
7. San Francisco Animal Care and Control  Coyotes  https://www.sfanimalcare.org/living-with-urban-wildlife/coyote-sightings/
8. The Humane Society of the United States  Coyotes and people: what to know if you see or encounter a coyote   https://www.humanesociety.org/resources/coyotes-people-encounters
9. The Guardian (3/9/2019)  Swooping magpie shot by Sydney council after ‘particularly aggressive’ attacks  https://www.theguardian.com/environment/2019/sep/03/sydney-council-shoots-aggressive-swooping-magpie
10. The Guardian (10/12/2017)  Magpie edges out white ibis and kookaburra as Australian bird of the year  https://www.theguardian.com/environment/2017/dec/11/magpie-edges-out-white-ibis-and-kookaburra-as-australian-bird-of-the-year
11. See for example Gren I-M, Haggmark-Svensson T, Eloffson K & Engelmann M (2018)  Economics of Wildlife Management – an overview  European Journal of Wildlife Research 64:22  https://link.springer.com/article/10.1007/s10344-018-1180-3  – start of Introduction
12. See for example Gren et al as 12 above, p 3
13. This can be confirmed at the IUCN Red list website https://www.iucnredlist.org/, entering in turn the names of the species.
14. Trotti, J 9/7/2018 The Human and Economic Costs of Power Cuts and Blackouts https://www.distributedenergy.com/home/article/13034360/the-human-and-economic-costs-of-power-cuts-and-blackouts
15. See for example Huter K et al 2016 Economic evaluation of health promotion for older people – methodological problems and challenges BMC Health Services Research 16 (Suppl 5) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5016726/
16. Positive.News 8/3/2017  Are you a human supremacist?  https://www.positive.news/environment/are-you-a-human-supremacist/
17. UK Government  Foxes, moles and mink: how to protect your property from damage  https://www.gov.uk/guidance/foxes-moles-and-mink-how-to-protect-your-property-from-damage
18. Hecht, L (2019) Optimal population density: trading off the quality and quantity of welfare   https://www.wildanimalinitiative.org/blog/optimalpopulationdensity   See especially the final paragraph.
19. Wikipedia  Population Ethics https://en.wikipedia.org/wiki/Population_ethics
20. I use the term Pareto improvement here in a specialised sense.  It is not implied that such a change would leave each individual human and each individual animal no worse off, only that overall welfare for humans and overall welfare for animals would both be improved.