Saturday, 25 June 2011

Amazed rats and super squirrels: urban animal adaptations

If I was the gambling sort I might be tempted to bet that the most of the large fauna in my neighbourhood was, like much of London, restricted to very few species: namely feral pigeons, rats, mice and foxes. The most interesting visitor to my garden is, judging by the size, a female common toad - the wondrously named Bufo bufo - which makes an appearance every couple of years to feast on snails and leave a shell midden behind.

After spotting a small flock of Indian-ringnecked Parakeets in our local park, I decided to look at the adaptations wildlife has undergone whilst living in an urban environment. After intermittently researching this topic over a month or so, I was surprised to find the BBC Science News website posting an article along similar lines. Synchronicity? I decided to plough ahead, since the subject is too interesting to abandon and I've got my very own experimental data as well, although it's hardly 'laboratory conditions' material.

Your friendly neighbourhood Bufo bufo
It's easy to see why animals are attracted to cities: the ever-present food scraps; the warmer microclimate; and of course plenty of places to use for shelter (my nickname for railway embankments is 'rodent condominiums'). Even the mortar in walls seems to offer smaller birds a mineral supplement (calcium carbonate) and/or mini-gastroliths (A.K.A. stomach grit) judging by the way they peck at them. Then there's also the plentiful sources of fresh water, which in my neighbourhood goes from birdbaths and guttering to streams and reservoirs. Who can blame animals for coming in from the cold? In the case of the London fox they have been arriving since the 1930s, whilst rodents were probably rubbing their paws together in glee as the first cities were being built many millennia ago in the Fertile Crescent.

There seem to be several, obvious behavioural changes that result from urban adaption, particularly when it comes to judging humans. I have found an astonishing lack of wariness in mice, squirrels and foxes, even in daylight, although rats are usually more circumspect. There are an increasing number of stories concerning foxes biting sleeping humans, including adults, even during the day. I was informed by a Clapham resident of how, having chased a noisy fox down the street at night, it then followed him back to his house, only stopping at the garden gate. Clearly there is some understanding of territorial boundaries here, too. This is supported by the behaviour of foxes in my area, which will happily chase cats in the local allotments even during the day, but once the cat emerges onto the street, the fox doesn't follow. Perhaps they have some understanding of connection between cats and humans?

City fauna has become more opportunist, prepared to scavenge meals from the enormous range of foodstuffs available in an urban environment, which around my area seems mostly to consist of fried chicken carcasses, usually still in the box. Even birds of prey such as the Red Kite (no small fry, with up to a one and three-quarter metre wing span) have recently been seen taking food off unwary children. This follows a period of finding food deliberately left out for them, so an association forms between people and food. This then is a two-way connection, with humans helping to generate changes in urban fauna by their own actions. Less time spent foraging means urban animals expend less physical energy, so there may a feedback loop at work here; if surplus energy can aid higher cognition, discrimination of humans and the urban environment increases, and thus even less time is required to source food. A facile conclusion perhaps, but read on for a possible real-life example.

My own experiments on grey squirrels took place about ten years ago, probably at least partially inspired by a television lager advertisement. It started when I found that my bird feeder was being misappropriated by a couple of squirrels. My first idea was to add radial spikes around the bird feeder using garden canes, but the squirrels were more nimble than I had thought, so after adding more and more spikes to create an object reminiscent of the Spanish Inquisition, I had to change tack. I next suspended the bird feeder on the end of a long rod that was too thin for the squirrels to climb on, but they managed to dislodge it at the wall end, causing it to drop to the ground for easy consumption. Rounds one and two to the pesky Sciurus carolinensis. My final design was a combination of spikes on the approach to the rod, the rod itself, then the feeder suspended from a long wire at the end of rod. I went off to work with an air of smug satisfaction that no mere rodent was going to get the better of me, only to find on my return that somehow the squirrels had leapt onto the rod and eaten through the wire!

One point to consider is that the bird food itself was in a transparent perspex tube, which is totally unlike any natural material. So when it comes down to it, are some animals, at least mammals and birds, over-endowed with grey matter when it comes to their usual environment, only utilising more of their potential when faced with artificial materials? Or do the challenges and rewards of being an urban sophisticate cause an increase in neurological activity or actual physiology? The latter gets my vote, if only for the evidence that supports this in human development. After all, the archaeological record suggests that modern humans and our ancestral/cousin species experienced an incredibly slow rate of technological development, with rapid increases only coming after disastrous setbacks such as the population bottleneck around 70,000 years ago, probably following a decade-long volcanic winter.

Experiments using rats in mazes over the past eighty years seem to agree with this thesis. However, there are clearly limits to animals' ability to learn new cognitive skills if they don't have time for repeated interactions, which may explain why most young foxes' first encounter with vehicular traffic is also their last. As for the BBC Science News report I mentioned earlier, research shows that birds with comparatively larger brain to body size ratios are those found to thrive in an urban environment. So it isn't all nature red in tooth and claw after all, but at least on occasion a case of brain over brawn for the city slickers.

Finally, I ought to mention a series of scare stories over the past year about another urban coloniser that seems to be returning after half a century's absence, namely the Cimicidae family of bloodsucking insects. With many of us using weaker laundry detergents at lower water temperatures, some researchers are predicting an imminent global pandemic of these unpleasant critters. So please be careful at night, and don't let the bed bugs bite!