50 years ago you wouldn’t have seen penguins in the streets of Simon’s Town. Today you can’t miss them.
Waddling along pavements, hiding under cars, nesting in gardens, African Penguins (Spheniscus demersus) have made themselves at home in this otherwise unremarkable slice of seaside suburbia close to Cape Town, South Africa.
The reasons for their sudden appearance are pretty clear. On the mainland, large predators had previously discouraged wandering penguins from making themselves at home, but increasing urbanisation along the coast meant fewer predators, and an opening appeared for the penguins. It’s a niche which today they fill with gusto, their distinctive braying calls echoing across town. While African penguin numbers in general are in decline, urban retreats like this are prime new real estate.
Versions of this same story are being played out in cities around the world. While evolution is driven by adaptation to change, humans are now the largest cause of that change on the planet. As we replace trees with buildings and rivers with roads, the most adaptable creatures are able to carve themselves out brand new niches. We might think of evolution as something that occurs only in the thickest of rainforests or most primordial of soups, but it is urban development that is leading to nature as we’ve never seen it before.
Consider the fact that cities make animals smarter. Studies have shown that Barbados bullfinches (Loxigilla barbadensis) living in the city are cleverer than their rural cousins. Their problem-solving skills have been sharpened by the challenges of city life. This is a trait shared by raccoons, amongst whom city dwellers are better at breaking into sealed garbage cans than their rural counterparts. Urban coyotes are pretty sharp too - they have been filmed observing traffic patterns to work out the safest time to cross busy roads.
It’s the smaller creatures who are perhaps making the most of city life. One study of New York City’s Broadway and West street has shown that nearly 1000kg of food waste (to put it in the local lingo that’s about 60,000 hot dogs) is cleaned up each year by insects. And you thought the forest floor was rich with food!
Spiders are also enjoying the hot city nights. Heat absorbed by all that concrete can turn urban areas into “heat islands”, making them up to 3°C warmer than surrounding rural land. Together with increased insect prey attracted by city lights, this may account for the fact that orb weaving spiders grow larger and are more fertile in the city than in the countryside.
We all know that city life can be stressful; this is just as true for animals, who can “burn out” in the same way as any high-powered executive. It is all down to elevated stress hormones. These are vital responses to pressing short term problems. They divert resources from long-term processes like the immune system to powering systems that deal with emergencies, like improving muscle function when you are trying to run away from a predator, or deal with a stressful meeting!
But if these hormones are at high levels for long periods, then in animals - just as in humans - brain function, reproductive ability and immunity all deteriorate. European blackbirds (Turdus merula) have lived in cities for 200 years, and today birds born and raised in the city appear to be better adapted at keeping their cool than non-natives. This means they can reap the benefits of city life - nest sites, food sources, and a longer breeding season - without suffering the same ill effects of high levels of stress hormones. As for attracting a mate in the chaos of the concrete jungle, they’ve got that sorted too. City blackbirds have learned to sing louder and at higher frequencies to be heard over the din of traffic.
As more and more of the world’s human population becomes urbanised, it’s worth remembering that we’re not alone in the big city. And as we search for ways to make our cities more livable, and our city lives more sustainable, it’s possible that some of the answers might be right under our noses, in the hidden corners of our cities that nature is making its own.
Featured image © Charlotte Goswell