Sunday 7 April 2024

Wild Mammals of London

Arguably the single biggest threat to the continued survival of animal and plant species is loss of habitat. Even if an animal isn't actively hunted, the ever-growing human population means that there are simply fewer suitable places for them to live. Logging and the expansion of agriculture are probably the biggest factors here, at least in terms of the area affected, but it's hard to argue that the recent growth of urban sprawl isn't another.

The urban environment is obviously a difficult or impossible one for most wild mammals to exploit. House mice and rats are an obvious exception, and there are also domesticated pets, but for truly wild creatures it's a different matter. While it may no longer have (say) bison or wolves, upstate New York is still home to seven species of shrew, three moles, four hares or rabbits, 22 different kinds of rodent, ten bats, nine mustelids, two foxes, and three deer, plus coyotes, bobcats, raccoons, striped skunks, and black bears. Manhattan... not so much.

The UK, in comparison, has an even smaller number of wild mammal species due to a combination of being an island and a dense population requiring substantial agricultural land. (Yes, even including northern Scotland, the UK has a population density 72% higher than that of NYS). We do have New Yorkers easily beaten on bat species - we have seventeen of those - but that's it. Although some are locally endangered, most of those that survive have done so by learning to live alongside humans to at least some extent. In some cases, that can include exploiting urban habitats.

For the right sort of animal, urban environments aren't as bad as one might think. They contain parks, gardens, allotments, and patches of undeveloped land that can provide dense plant cover that's great for hiding and nesting, and there's plenty of edible refuse left lying about if you're the sort of animal that's willing to eat it. Against this, of course, we have to set the dangers from cars, pollution, nighttime street lighting, and free-roaming cats, plus the basic fact that quite a lot of it is concreted over.

Research on how animals cope with urban expansion has been uneven, concentrated primarily in Europe and North America. This, while unsurprising, is something of a pity, as the most rapid urban expansions in recent years have been in the Global South - seventeen of the twenty fastest-growing urban areas in the world are in Africa, while Hyderabad and Kinshasa are the latest places to join the "megacity" club of urban areas with a population of over 10 million. But we have the data that we have and there happens to be one well-studied area close to me.

London is, of course, the largest urban area in the UK. The officially recorded population is 8.9 million, but the sprawl extends well beyond the administrative boundaries, with the OECD's estimate of the total urban population being a little over 12 million in 2022 - about the same as Los Angeles. As the mention of gardens and parks above indicates, this isn't all high-density shopping streets, tower blocks, and commercial centres and, even if we ignore the mice and rats there are certainly non-domesticated animals living in the built-up area. However, different mammal species will have different requirements, and therefore different tolerances for what they can put up with in terms of urbanisation. So just how good is the habitat for the different wild species that call London home?

A recent survey used citizen science reports by members of the public of wild mammals seen across the Greater London area and reported to the Greenspace Information database and the National Biodiversity Network. It considered four species living wild in the UK: badgers (Meles meles), red foxes (Vulpes vulpes), hedgehogs (Erinaceus europaeus), and grey squirrels (Sciurus carolinensis). The last of these, it's worth pointing out, is not native to the British Isles, being an import from the US, but has done well enough to become widespread across most of England and Wales.

The survey considered six different types of green habitat in the London area, with the remainder being either open water or road surfaces and pavements. Parkland is perhaps the most obvious of the green habitats we would associate with urban areas, but gardens, while much smaller individually, collectively cover an even larger area (since much of Greater London is, of course, suburban). Hedgehogs, it turns out, favour both gardens and parks. These often contain bushes and even trees, and often have a range of vegetation that's dense enough to provide shelter for small mammals. Furthermore, gardens often contain compost heaps, which are great if you want to find earthworms to eat and may include other food sources, too - some placed there deliberately, because hedgehogs are popular animals and they are intelligent enough to remember in which gardens such food can be found.

Foxes also favour gardens, but are less common in parks. This may be due to the fact that there's likely to be edible refuse nearby, while another factor that makes many parks less attractive to wild animals than garden greenery may be the relative lack of undergrowth and a lower diversity of vegetation. (This may, of course, depend on the garden, but "parks" here include public play areas that are likely to have little more than regularly mown grass). 

Allotments were classified separately from gardens in the study, but showed a similar pattern of wild animal use. I'm told these are called "community gardens" in America, but, for those unfamiliar with the term we're talking about small plots of agricultural land used for non-profit growing of vegetables by the local residents. They are less likely to include trees than gardens, but the crops and vegetation are good for insects, and what's good for insects is good for the hedgehogs that eat them.

London also includes some areas of outright woodland, such as Wimbledon Common and Oxleas Wood. This might seem ideal habitat for just about any wild animal native to the area, but, in fact, foxes and hedgehogs are less often reported there than elsewhere. In the case of foxes, the lack of edible refuse may again be a factor and it's conceivable that the hedgehogs also find it more effort to forage here than they do in gardens. Then again, the authors point out, it may just be difficult to spot hedgehogs hiding in wooded undergrowth, and they are less likely to be seen by passing locals. 

Badgers, on the other hand, love woodland; all those tree roots are good for constructing their setts, and the undergrowth is heavy enough to provide them with cover. Squirrels, for understandable reasons, are also fans of anywhere that has plentiful trees. This, it turns out, includes not just undeveloped woodland, but cemeteries, a habitat type that also includes long grass and a comparative lack of human disturbance, making it easier for foxes to hunt.

The final category of greenspace considered in the study is described as "public amenity", referring to small patches of greenery found around hospitals and schools, or as landscaping in residential areas. Only badgers seemed to favour this type of habitat, perhaps finding it easier to locate food in short grass.

In general, urban animals are more common in city areas where the population density is at its lowest, such as the suburbs, and where the traffic is least busy. Hedgehogs are a slight oddity here, since they are more commonly seen in areas with heavy traffic. This has been shown in previous studies too, but could be due to them often being "sighted" when they show up as roadkill, something hedgehogs seem sadly prone to.

Putting this together with maps of the Greater London area shows that badgers are the least adapted of the four species to urban life. They are found in such areas, and there is some evidence that urban badgers are becoming more common in Switzerland, but it seems that they still prefer the quietest and least built-up parts of the city. In London, this means places like the Woodridge Nature Reserve and Richmond Park, both on the periphery of the metropolitan area.

Those areas are about as close to rural as one can get without leaving Greater London, but hedgehogs turn out to be particularly well suited to life in the suburbs. They are least commonly seen in the places that badgers prefer, and are most frequently spotted in the 'Outer London' boroughs, with notable hotspots in Bromley, Enfield, and Havering, but for the most part, are fairly well spread out wherever they are large suburban gardens.

Of the four animals in the study, foxes are the best adapted to urban living, being more common in Inner London than they are in the outer boroughs. They are perhaps the most commonly seen wild animals in British cities, despite the fact that they don't seem to have taken up urban living much prior to the 20th century. The same pattern is seen in other countries across the world where the species is native from Italy to Japan. Indeed, it's by no means rare to see them away from greenspaces - they certainly trot down the streets where I live in the predawn light, likely hoping that somebody has left their food waste out overnight in easily tearable bin bags.

The distribution of grey squirrels is perhaps the surprise here, however, because they too are concentrated in Inner London, and even more so than the foxes, being at their most common in Westminster and The City. (The latter, for those unfamiliar with it, being that part of London formerly surrounded by the medieval city walls). This is because squirrels are common where there are trees, but not gardens, and the very centre of London actually has quite a few green squares, roadside trees, and the like.

That may not be true of every city, but, at least in central London, it's relatively easy for grey squirrels to get about. With the right sort of city planning, urban squirrels may actually become more common as the city expands in the future.

[Photo by "Ibonzer" from Wikimedia Commons.]

1 comment:

  1. This comment has been removed by a blog administrator.