Behaving in an Urban World

This is a guest post by Monash University PhD student Will Sowersby. 

You may have noticed that the world around you is changing. In fact, it is doing so at an unprecedented pace. Today, half of the world’s population live in cities and by 2050, that figure will be over 70%. In evolutionary terms, this rate of urban development represents a radical ecological upheaval. It is the sort of change that, in the past, generally occurred over geological time, not within generations. The process of urbanization often results in a loss of biodiversity due to the destruction and fragmentation of habitat, as well as the exposure of animals to artificial stimulations and pollutants. In many ways, we might expect such radical changes to leave our cities totally devoid of life, or only inhabited by the few hardiest species. Instead, more and more animals appear to be adjusting to and exploiting life on the streets. Peregrine falcons are nesting in skyscrapers instead of towering trees and crows are using passing cars as nut-crackers.

How have these species adapted? Well, the first way an animal responds to changes in its environment is by altering its behaviour. In this regard, the ability to adjust behaviour to changes in the environment can mean the difference between a population surviving and going extinct. Recently, the importance of studying animal behaviour in urban settings has become a hot topic in behavioural ecology: the area of science that explores how behaviour shapes – and is shaped by – the environment. By studying the behaviour of animals in urban areas, we can further our understanding of why some species have flourished, why others have not, and what measures we can take to help wildlife live in our cities and decrease biodiversity loss in urban areas.

So what allows some species to flourish in urban environments, while others fail? Some may simply have an inherent set of behaviours and life history traits that make them ‘pre-adapted’ to city life. Often, such animals have also benefited because urban settings have eliminated competitors and provided additional food sources. In Melbourne, for example, aggressive social birds such as noisy miners have flourished, often to the detriment of smaller, native bird species. Similarly, most Melbournians will be familiar with the grunts and hisses of the brushtail possum, an opportunistic marsupial that has benefited from feeding on our gardens, inhabiting our rooves and even taking a free feed from well-meaning residents.

The noisy miner is one of many bird species flourishing in urban environments.  Photo: Emma Walsh

The noisy miner is one of many bird species flourishing in urban environments. Photo: Emma Walsh

Many of the animals we now see reappearing in our cities and suburbs differ greatly from their bush and rural counterparts. For example, many urban populations – including birds, lizards and mammals – are significantly bolder than non-urban animals. Bolder animals may be better able to cope with human activity, less likely to retreat from threats, and quicker to exploit new food sources. Furthermore, urban animals also get less stressed. That is, they release less stress hormones than non-urban animals, which would be beneficial for living in a highly stimulating and chaotic environment. Remarkably, some animals have even begun to learn the rhythms of our cities, such as watching for traffic and crossing roads when traffic lights are red.

We have only recently become aware that many animals exhibit consistent “personalities”, or more accurately, behavioural types. Certain behavioural types correlate within an individual (e.g. aggressiveness and boldness) to form what is called a ‘behavioural syndrome’. Behavioural syndromes are considered to be largely inflexible across contexts and are likely to be heritable. Therefore, individuals inhabiting urban environments may have a set of inherent behaviours that have allowed them to more readily adjust. This means that other individuals in a population may not be able to demonstrate appropriate behaviours in urban environments. Consequently, urban animal populations may have a lower diversity of behavioural types compared to non-urban populations, and a lack of diversity is rarely (if ever!) a good thing.

The common brushtail possum is a familiar sight for many in suburban Melbourne.  Photo: Dr Carlo Kopp

The common brushtail possum is a familiar sight for many in suburban Melbourne. Photo: Dr Carlo Kopp

Artificial light has well known effects on animal behaviour (refer to a recent Wild Melbourne post by Anne Aulsebrook) and so does anthropogenic noise. Many frog species around Melbourne are being drowned out by traffic noise, impacting the chances of males attracting mates. One species, the southern brown tree frog, is offsetting this by raising the pitch of its calls in noisy environments, so that males can be heard from further away. Noise pollution is also forcing urban birds to adjust their vocal communications or risk going unheard. Urban silvereyes are much louder than their rural counterparts, while urban noisy miners can even adjust the volume of their calls depending on whether they are near busy or quiet roads. 

Chemical pollutants that are getting into the environment are also having a dramatic effect on the behaviour of wildlife. For example, hormones used in agriculture in Australia, which leach into our waterways, can alter the mating behaviour and morphology of freshwater fish. Furthermore, chemicals used in the human female contraceptive pill are the likely cause of feminization in fish, which has a significant impact on their ability to breed.

Growling grass frogs are one species that may be suffering due to traffic noise.  Photo: Peter Robertson

Growling grass frogs are one species that may be suffering due to traffic noise. Photo: Peter Robertson

How can we use our knowledge of animal behaviour to minimise the impacts of urbanisation and to encourage animals to return to our urban spaces? We should firstly feel encouraged by the fact that we can coexist with wildlife. By offering native animals a wide choice of native vegetation and large, undeveloped areas in our cities, we can increase both the diversity of species and the diversity of individuals within species in our urban spaces. By knowing how and when animals move through the landscape, we can create safer passageways for them. Already, road-crossing structures are allowing some of Victoria’s rare arboreal marsupials to safely cross highways, while crossing structures are helping red crabs on Christmas Island to make their annual migration. Elsewhere, cities are turning the lights off in large buildings at night, so that migratory birds are not distracted as they fly past. We could do the same here in Melbourne (at key times during the year), along with implementing stricter pollution controls (particularly in sewage and wastewater treatment plants), lowering noise pollution, decreasing vegetation clearance, not feeding wild animals and keeping cats inside (particularly at night). Ultimately, a city shared with wildlife is not only healthier for us, but also far more interesting. By beginning to understand the creatures around us, we can make sure our cities are not only home for us, but for them too.

Banner photo courtesy of Anne Aulsebrook.