Do wild boars eat better or worse after they move into the city?

Wild boars were spotted on the streets of Nanjing again. This time, a small wild boar crossed the road and got stuck in the guardrail because it was too fat. From Nanjing University in the suburbs to milk tea shops in shopping malls, wild boars frequently appear in Nanjing, making the city nicknamed "Wild Boar City". However, this is just a small microcosm of wild animals entering the city.

Wild boar: It’s a bit embarrassing | Weibo: @中国警察网

Urbanization is one of the most extreme forms of human environmental change. The expansion of cities has significantly changed natural habitats - large tracts of land have been developed and transformed, and the degree of its drastic transformation is far greater than that of traditional agriculture and logging. Some animals choose to retreat to smaller natural habitats, while others voluntarily or are forced to come to cities to coexist with humans.

However, for animals entering cities, there are hidden challenges everywhere, from eating, drinking, living and traveling to contact with humans. Take food for example. Some people think that there are more nutritious foods in cities, while others worry that food in cities is not suitable for wild animals. Do cities really make life better for animals?

Is eating better or worse in the city?

It is not surprising that wild boars (Sus scrofa) have entered Nanjing. Wild boars are one of the most widespread mammals in the world. They are very flexible in their behavior and can effectively utilize the concrete jungles and low-diversity habitats in cities . The proliferation of wild boars in urban areas is a global problem. Some European and American countries have even opened up hunting tourism, allowing tourists to hunt pigs with guns. Some farmers have even used helicopters to improve the efficiency of killing wild boars.

A herd of wild boars forage in a garbage dump on the outskirts of Berlin | Domski3 / Wikimedia Commons

One important reason why wild boars have been so successful in settling in cities is that they are not picky eaters. For animals that are not so picky, they can obtain a variety of foods in cities, including human garbage, crops (fruits and vegetables), small mammals, birds, pets, livestock or food fed by humans. In Spain, wild boars living in the urban area of ​​Barcelona often eat human food, which is often high in nutrition, than their cousins ​​living in non-urban areas . This also leads to changes in physiological characteristics: urban wild boars are larger, have higher body weights, and have higher triglyceride levels in their blood.

In order to adapt to the environment, the activities of urban wild boars are also very different from those in their original environment. In order to avoid humans, they are almost only active at night ; due to space constraints, their range of activities is also smaller. However, due to the increased difficulty of foraging in the city, their daily activity volume is twice that of wild boars in their natural habitat . This shows that they can flexibly adjust their lifestyle according to different environmental conditions, which allows their population in the city to grow rapidly.

In Barcelona, ​​targeting wild boars with tranquilizers | SEFaS/Ajutament de Barcelona

Wild boars flexibly change their activities and eating habits according to the urban environment. This phenomenon is called "adaptive response", which usually manifests itself within a few days to weeks after the animals enter the city. The high adaptability of wild boars makes them " urban pioneers "; those with slightly lower adaptability are " urban adapters ", such as some animals that are accustomed to eating insects and plant seeds. Both types of animals can successfully adapt to the urban environment. They will actively enter the city, use human resources, and settle down in the city. They are true urban residents. Their density in cities is often higher than in rural areas, and even higher than in natural habitats. Therefore, wild boars often become the protagonists of urban news.

Some carnivores are " city avoiders ", such as some small canines, which are more likely to conflict with pet cats and dogs in cities. For those supercarnivores - animals whose diet consists of 70% meat, such as bobcats (Lynx rufus) and weasels (Mustela sibirica), they need to hunt live prey, so they tend to actively avoid urban areas , only occasionally use human resources, and still rely mainly on natural resources. These animals are often found in areas bordering urban suburbs and natural habitats, where human density is lower and more natural environments are preserved.

Weasels, which need a lot of meat, are less fond of cities. | Dibyendu Ash / Wikimedia Commons

Not all animals like to live in cities. This is related not only to the habits of different animals, but also to the differences in urban environments. Different cities have completely different spatial scopes, population densities, urban forms and geographical locations - each city needs to be analyzed separately, and animals will also respond specifically to specific cities. The reason why Nanjing attracts so many wild boars is that the natural conditions in Nanjing are very suitable for wild boars : there are not only widely distributed hills, but also many water systems. The diversity of terrain provides a good habitat and food source for wild boars, and the density of wild boar populations in urban areas has increased year by year. Fortunately, in Nanjing, the activities of wild boar residents are limited to swimming and walking, and there has been no news of Nanjing citizens being attacked by wild boars.

Is it safer or more dangerous in the city?

In Nara Prefecture, Japan, the city is full of about 1,000 sika deer (Cervus nippon nippon), which live here all year round. What attracts these large ungulates to the bustling metropolis? In addition to the natural environment, the settlement of sika deer here is largely related to their interaction with humans: tourists can buy snacks "deer senbei" to feed them, and some sika deer are no longer wary of humans and even beg for food from humans. These bolder individuals can get significantly more food from humans - this not only allows them to live better in the city, but also brings survival advantages to their offspring.

Sika deer in Nara | Dariusz Jemielniak / Wikimedia Commons

The case of Nara's sika deer may support the " predator relaxation " hypothesis for urban wildlife. This theory holds that cities are safer than natural habitats because there are fewer predators . Therefore, wildlife's vigilance behaviors to detect predators are less important, and they are spent less time and less frequently on detecting predators.

The opposite hypothesis is the " predation diffusion " theory. This theory predicts that some predators can adapt to urban environments and increase population density, so it is easier for prey to be preyed on in urban areas . In addition, in highly urbanized areas, habitats are highly fragmented due to the cutting of roads and buildings, and animals may be forced to stay in the same habitat as their natural enemies. Moreover, the most important residents in cities - humans - also bring new risks to wildlife. For example, half of New York residents said that they almost hit a deer while driving. With new and old risks appearing at the same time, wildlife in cities may have to strengthen their vigilance behavior and therefore sacrifice some of their foraging time.

New York authorities even need to remind citizens that fall is the season when deer are active, and vehicles should be careful of deer on the road｜Observer-Dispatch

These two hypotheses have been confirmed in different studies. As far as the limited research available so far is concerned, **birds in cities are significantly less likely to be preyed on than their counterparts in rural areas. **Mammals in cities also seem to relax their vigilance. Wild boars are less alert than in the wild. If they fall into traps set by humans, they will not stay away from the area around the traps after being released.

Unfortunately, research data other than birds is still scarce. But what is certain is that because the threats posed by urban environments are so varied and complex , wild animals need to flexibly adjust their responses and change their vigilance behaviors within hours or even seconds in response to external stimuli and environmental conditions - this has become an essential skill for them to live in cities.

Blue tits living near humans have even learned to steal milk | Steve Magennis

In the city, have we become braver or braver?

Will the personalities of wild animals change when living in cities? This may be the most challenging question when discussing the impact of cities on wildlife. Professor Kay Holekamp of Michigan State University tried to explore this question.

Researchers use boxes to study the boldness of young spotted hyenas | References [7]

They gave spotted hyenas (Crocuta crocuta) a series of small puzzles and found that young spotted hyenas living in areas with high human disturbance were more exploratory of objects they had never seen before, which helped them exploit new resources and use new habitats, but they were more timid when faced with boxes containing food. This increase in exploratory behavior is consistent with birds and small mammals in cities, but this decrease in boldness is the opposite of theirs.

Researchers speculate that the reason why young spotted hyenas are timid may be that these large mammals are more likely to cause fear and hatred in humans, and therefore are more likely to be involved in conflicts with humans - being driven away or even killed by humans. This threat forces them to curb their boldness and risky behavior.

Spotted hyenas in Amboseli National Park, Kenya | Sara&Joachim / Wikimedia Commons

Boldness reflects an animal's tendency to take risks, while exploratoryness is about how they respond to new things and new environments. These two are key personality traits of wild animals, and they are not only affected by human disturbance in cities, but also have a profound impact - animals with different personality traits have different behaviors such as foraging and responding to predators, and thus have different survival and reproduction situations. These personality changes may also be passed on to the next generation through physiological changes and behaviors , but these changes require years or even decades of accumulation before we can observe them.

How to live in harmony with animal residents?

Conflicts between humans and animals are always a big problem. Large animals living near humans may cause damage to livestock or humans, but this also brings risks to the animals - humans may harm them through large-scale poisoning and other means.

Rural areas have some experience with this problem. For example, in Xishuangbanna, Yunnan, conservationists set up buffer zones at the edge of elephant settlements and planted food that elephants love. When elephants are full in the buffer zones, they rarely harass farmland and do not harm farmers' interests. This solution has also been promoted in other countries that are plagued by elephant harassment.

Set up a buffer zone for elephants | People's Daily Online

But the situation in cities is more complicated. The damage caused by animals in cities is often not as obvious as elephants trampling on farmland. Therefore, fencing them or even killing them directly - these traditional ways of mitigating conflicts are difficult to accept by the public. Moreover, human feeding of wild animals can have the opposite effect, encouraging animals to adapt to cities. The most effective and acceptable way at present is to selectively remove "problem animals" - animals that cause major damage and are often the more daring individuals in the group - from cities .

The limited means we have to address this problem is also related to the insufficient amount of research. So far, we still know a lot about how wildlife adapt to cities. But changes in wildlife behavior are often a precursor to conflicts with humans. Therefore, research in this area is an indispensable part of wildlife management. Only by knowing what happens to our animal neighbors in cities can we coexist with them more harmoniously on this increasingly urbanized and humanized planet.

References

[1] Barua, M., et al. (2013). "The hidden dimensions of human-wildlife conflict: Health impacts, opportunity and transaction costs." Biological Conservation 157: 309-316.

[2] Castillo-Contreras, R., et al. (2021). "Wild boar in the city: Phenotypic responses to urbanization." Science of the Total Environment 773.

[3] Contesse, P., et al. (2004). "The diet of urban foxes (Vulpes vulpes) and the availability of anthropogenic food in the city of Zurich, Switzerland." Mammalian Biology 69(2): 81-95.

[4] Ellington, EH and SD Gehrt (2019). "Behavioral responses by an apex predator to urbanization." Behavioral Ecology 30(3): 821-829.

[5] Eotvos, CB, et al. (2018). "A meta-analysis indicates reduced predation pressure with increasing urbanization." Landscape and Urban Planning 180: 54-59.

[6] Gallo, T., et al. (2019). "Urbanization alters predator-avoidance behaviors." Journal of Animal Ecology 88(5): 793-803.

[7] Greenberg, JR and KE Holekamp (2017). "Human disturbance affects personality development in a wild carnivore." Animal Behavior 132: 303-312.

[8] Newsome, SD, et al. (2015). "Individual variation in anthropogenic resource use in an urban carnivore." Oecologia 178(1): 115-128.

[9] Noske, R. (1998). "Breeding biology, demography and success of the rufous-banded honeyeater, Conopophila albogularis, in Darwin, a monsoonal tropical city." Wildlife Research 25(4): 339-356.

[10] Podgorski, T., et al. (2013). "Spatiotemporal behavioral plasticity of wild boar (Sus scrofa) under contrasting conditions of human pressure: primeval forest and metropolitan area." Journal of Mammalogy 94(1): 109-119.

[11] Ripple, WJ, et al. (2014). "Status and Ecological Effects of the World's Largest Carnivores." Science 343(6167): 151-+.

[12] Ritzel, K. and T. Gallo (2020). "Behavior Change in Urban Mammals: A Systematic Review." Frontiers in Ecology and Evolution 8.

[13] Rutten, A., et al. (2019). "Future distribution of wild boar in a highly anthropogenic landscape: Models combining hunting bag and citizen science data." Ecological Modeling 411.

[14] Sol, D., et al. (2013). "Behavioral adjustments for a life in the city." Animal Behavior 85(5): 1101-1112.

[15] Sorace, A. (2002). "High density of bird and pest species in urban habitats and the role of predator abundance." Ornis Fennica 79(2): 60-71.

[16] Stillfried, M., et al. (2017). "Secrets of Success in a Landscape of Fear: Urban Wild Boar Adjust Risk Perception and Tolerate Disturbance." Frontiers in Ecology and Evolution 5.

[17] UnitedNations (2018). "Revision of world urbanization prospects." United Nations: New York, NY, USA 799.

[18] Van Helden, BE, et al. (2018). "Use of urban bushland remnants by the western ringtail possum (Pseudocheirus occidentalis): short-term home-range size and habitat use in Albany, Western Australia." Australian Mammalogy 40(2): 173-180.

[19] Vila, C., et al. (1997). "Multiple and ancient origins of the domestic dog." Science 276(5319): 1687-1689.

Author: Yu Cong

Editor: Mai Mai

This article comes from the Species Calendar, welcome to forward