Life in the city: urban carnivores

by Bill Bateman & Trish Fleming.  Our paper “Bateman P.W. & Fleming P.A. (2012). Review Article. Big city life: carnivores in urban environments. Journal of Zoology, 287, 1–23” has made it on to the list top cited papers of 2013 for Journal of Zoology.  Obviously enough, it pleases us that our research is making an impact.  But it is also worth thinking about why this review is making an impact.  Why is the success, or otherwise, of some taxa in urban areas worth exploring?

We live in an urbanised world: more people live in some sort of modernised, urban conurbation than do not, and the size and fundamental nature of cities is also changing.  Cities now contain millions of people, the landscape within urban areas is one of small patches of green ­­­surrounded by concrete, metal and stone, with most soil covered up and the majority of water flow directed and managed.  Even across farmland and small villages, human activities are influencing our environment.  Where, in all this, is there room for wildlife?

Well, undoubtedly much of the wildlife that used to live where cities now are, have gone.  The large mammals, the mega carnivores, the specialists, the species that are susceptible to disturbance.  These species are all ‘urban avoiders’.  At the other extreme, synanthropic species (e.g. rats, mice, cockroaches, pigeons) are ‘urban exploiters’ – making use of copious resources such as refuse available in cities to reach higher densities than they are found under natural environments.  Between these two extremes are the ‘urban adapters’, animals that opportunistically live alongside us in cities.

In this paper, we reviewed the presence of carnivores in cities.  What makes species like the red fox, Eurasian badger, raccoon, stone marten and bandicoot successful in cities?  The graph below looks at the body size of carnivores by family and by success as an urban carnivore.

graph1

Regardless of family, urban carnivores are medium-sized generalists.  Big carnivores may be too obvious and threatening; small animals find it hard to move around the urban matrix.

Urban carnivores can have access to so much food that territories collapse and multiple individuals live the life of Riley in an urban paradise.  Foxes in Zurich have stomachs crammed with leftover takeaway food, while raccoons in a city in Florida reach four hundred times the density of populations in non-urban areas.

This is not to say that life is easy in the big city, or even in a small town.  Roads are bad news for most species and road kill is one of the most common causes of death for many urban carnivores (although it is sometimes difficult to tell how common, as comparable data for mortality for non-urban populations is often lacking; see the figure from our paper below).

graph2

So, getting to the point, why does this paper matter?  As cities spread, perhaps we need to think of their value as conservation areas (for some species at least).  We need to make a choice about whether we welcome or reject urban carnivores, and we need to make a plan about how we do that.

There may be space in some cities for even the big carnivores: American black bears seem to do well in some cities.  Female bears in urban areas breed younger although those young rarely get to breed themselves, and mortality rates are high.  Are there practices and policies we can develop and implement that would allow these carnivores to live peacefully alongside humans in urban landscapes?

Who wants to live in an environment with no animals?  We need more research to ensure that doesn’t happen, not just in the last remaining wilderness spaces of the world, but also in the towns and cities in which we live.

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