Using camera traps to assess the impact of urbanisation on mammals in Durham, UK

Toby Atkinson-Coyle recently graduated from the biology department at Durham University: congratulations Toby! For his final year project, Toby worked with the MammalWeb team on a camera trapping project looking at the impact of urbanisation on mammals in Durham. Here, he writes about some of the findings from his project:

For my masters’ project, I used distance sampling with camera traps to assess the impact of urbanisation on mammals in Durham, UK. As discussed in previous posts, this method involves measuring the distance of animals from the camera which can then be used to calculate their density. I deployed cameras in both rural and urban habitats across a 3x4km area of Durham from 12th February through to 9th March 2018.

Over the study period, a total of 2,646 images of wild mammals were obtained, 1,285 in rural and 1,361 in urban habitats (see Figure 1). Six species were regularly detected in both habitats, including European rabbit, European badger, red fox, grey squirrel, roe deer and small rodents. European rabbit and grey squirrel were the most frequently photographed species, so I report on them in greater detail. To assess the overall impact of urbanisation on mammals, I was also able to calculate broader community-level metrics such as species richness.

Figure 1 A subset of mammals photographed in Durham, UK.

Species varied in density between habitats. Four out of the six detected mammal species decreased from rural to urban habitats whilst two increased. The largest differences in density were in rabbit and grey squirrel populations. Rabbit density in urban habitats was twice that in rural ones (see Figure 2A). Conversely, squirrel density was much greater in rural habitats (see Figure 2B).

Figure 2 Estimated density per km² of European rabbit and grey squirrel populations in rural and urban habitats.

I calculated species richness per deployment by counting the number of different species detected by each camera. Species richness was higher in rural habitats with an average of 1.60 (0.29 SE) species detected per deployment whilst in urban only 1.12 (0.23 SE) species were detected (see Figure 3).

Figure 3 Species richness per deployment of mammals in rural and urban habitats.

Urbanisation has a range of impacts on mammals at both the species and community levels. Broader ecological metrics indicate an overall decline of mammals with urbanisation but, at the species level, some appeared to benefit. Therefore, it is important to consider a range of species and community-level metrics when assessing the response of wildlife to disturbance.