Colonizer’s guide to settling in the city
When I started studying urbanization I was surprised by how many animals live in cities. This lead to questions like: why do animals visit cities, what makes them stay, and does living in the city create new opportunities? Evidence is growing that cities are hotspots for observing and studying contemporary evolution: city animals have access to new sources of food, refuge from predators, and other ecological opportunities. Some animals exploit these opportunities, and over time differences can arise between those that exploit cities and the species that remain in their less-disturbed natural habitats.
Cities are, in general, full of humans! Because of that, urban animals have to learn to live among us. There are many ways in which cities influence animal behaviors. For example, urban squirrels and urban gulls alter their escape behaviors in response to human presence. If urban animals were constantly running away from us, it would be energetically costly. Many researchers hypothesized that urban animals should learn to ignore humans and settle in closer proximity to human areas. Could boldness/exploration be necessary for urban life? If so, behavior could be a filtering process where the shy have no place in the city. But perhaps, animals that have flexible behaviors and can learn quickly are favored in cities. At the moment more work needs to be done to address some of these questions.
The trickster finds a new home in the city
A new study by Breck et al., asks how behavior differs between rural and urban coyotes. Coyotes are interesting to study because of potential for wildlife/human conflicts. These medium-sized predators can approach humans, forage directly from their trash bins, and might prey on pets or bite humans. Coyotes have also colonized every mayor city in the continental United States creating the opportunity to study contrasts in behavior over a large range.
To better understand the behavior of urban and rural coyotes, Breck and collaborators did two experiments. First, they measured the distance at which coyotes would flee from an incoming threat. This metric is known as flight initiation distance and has been widely used as a metric of boldness. Shyer animals should flee at greater distances and bolder animals wait more before fleeing. But, the measure of flight initiation distance can be confounded by the animal’s perception of fear. For example, when there is more vegetation there is more cover which can lead to shorter distances before animals flee. To account for that, Breck quantified vegetation cover. In the second experiment, they used buried meat as an attractant to contrast number of coyote visits. To measure boldness, they added a new object around the meat in some trials. Animals that are shy would perceive this strange object with caution and should visit the food less.
They found vegetation cover was strongly associated with decreased flight initiation distance (Figure 1). But overall, urban coyotes had lower flight initiation distances at all cover levels compared to rural coyotes (i.e., they allowed closer approach before fleeing). When contrasting their behaviors during flight (bottom panel, Fig. 1) most rural coyote had an extremely frightful response (behavior response of 4) meaning that they ran away from their original spot without looking back. In contrast, urban coyotes often remained at least within 6 meters of their original location and looked back at the approaching human. In their second experiment, they found that urban coyotes visited the attractant more and were less deterred by the novel object. Only one rural coyote visited the attractant with the novel object.
No country for shy coyote, not quite!
Breck and collaborators point out that there is a lot of variation within urban and rural populations. Meaning that although most urban coyote were bolder, there were still shy responses in the city. This finding might be evidence that shy coyotes aren’t being filtered out from cities. Instead it’s likely that the behavioral flexibility and learning adaptability played a major role in the success of coyotes in cities. They also point that humans’ perception of coyote vary greatly between these two habitats. In rural areas humans actively trap, hunt and chase away coyotes. Also there are more natural predators like the mountain lions in rural areas. Both of those factors might discourage bold and exploratory behaviors in rural areas. In the city, coyotes can find food associated to humans through direct feedings or foraging human trash bins. Which might increase boldness and exploration of novel objects (like trash bins). I look forward to reading more studies specifically designed to disentangle some of these process that facilitate life the city!
To read more about this topic check out:
Beans C (2019) News Feature: Cities serve as testbeds for evolutionary change. Proc Natl Acad Sci U S A 116:2787–2790. doi: 10.1073/pnas.1820852116
Breck SW, Poessel SA, Mahoney P, Young JK (2019) The intrepid urban coyote: a comparison of bold and exploratory behavior in coyotes from urban and rural environments. Sci Rep 9:2104. doi: 10.1038/s41598-019-38543-5
Feature image at top by: Jitze Couperus (flickr.com)
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