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Lights, Camera, Tracks! The Presence of Mammals in Residential Yards

In this article, scientists examine different land uses, from urban to suburban to rural landscapes, and their effects on wildlife. In particular, the scientists examine how different features of these landscapes affect the mammal populations found in residential yards. The scientists also wanted to know how human-provided resources and disturbances - like gardens, feeders, lights, fences, etc. - might affect mammal populations in these yards.

Lights, Camera, Tracks! The Presence of Mammals in Residential Yards

Meet the Scientists

Aaron Grade

Ecologist

Paige Warren

Urban Ecologist

Susannah Lerman

Ecologist | Wildlife Biologist

What Kinds of Scientists Did This Research?

Ecologist: This scientist studies the relationship between living things and their environment.
Wildlife Biologist: This scientist studies wildlife, including what they eat, how they reproduce, and how they use their habitat.
Urban Ecologist: This scientist studies the relationship of living organisms with each other and their surroundings in an urban environment, such as yards and city parks.

Thinking About Science

Ecology is the study of ecosystems. Ecosystems are groups of living things that interact with nonliving things in the environment. One example of an ecosystem is a pond. In a pond, there are living things like insects, fish, and plants interacting with nonliving things like the water and rocks. Another type of ecosystem is a park in a city. Parks can have living things like plants, people, and wild animals interacting with nonliving things like water, rocks, playground equipment, and sidewalks.

Ecosystems can also exist on a larger scale. The city park in the last example is an ecosystem, and that city park is also part of the larger ecosystem of the city (figure 1).

Aerial view of central park. There is a green space between large sky scrapers. — **Figure 1**. This aerial view of Central Park in New York City shows the park with the city surrounding it.

In the city, living things like birds, insects, squirrels, other wildlife, and humans interact with the nonliving things like roads, buildings, and cars. Studying ecosystems in a city is a special field of ecology called urban ecology. Scientists who study ecosystems in cities, and the areas near cities, are often called urban ecologists.

Thinking About the Environment

Ecosystems may contain many different types of habitats. A habitat is a place where a plant, animal, or other organism would naturally grow. For example, a prairie dog habitat is flat, dry grassland areas with few people (figure 2).

A prairie dog standing on its hind legs in a field — **Figure 2**. Prairie dogs live in colonies in open grassland areas.

Human activities like construction and urbanization or natural causes like a volcano erupting may destroy parts of a habitat. The habitat may then be broken or fragmented into smaller pieces (figure 3). This process is called habitat fragmentation.

An excavator clearing trees and other debris — **Figure 3**. Habitat fragmentation can occur for a variety of reasons including natural causes like the eruption of a volcano or human causes like building a new neighborhood.

Habitat fragmentation may cause problems for animals and plants in their habitat. For example, if a highway is built through an animal’s habitat, the animal may have to cross the highway to get to resources it needs. By crossing the highway, the animal may be at risk of getting hit by an automobile. In some areas, people have installed wildlife crossovers to help with this problem (figure 4).

two wildlife crossroads shown as bridges over bust roads — **Figure 4**. Wildlife crossovers are being used in some areas to help with habitat fragmentation.

In this study, the scientists look at how habitat and land use context affect mammals. Specifically, the scientists look at what happens when land use context changes from urban to suburban to rural areas and how that impacts mammals in the area.

Introduction

Most people in the United States live in urban areas. The word “urban” can be defined in many ways. Scientists in this study define it as places that are dominated by humans and human-built features, like buildings, roads, parks, and yards. These urban areas, though, can be very different from each other.

The land use context, or how the land is used, around an urban neighborhood may be very different from one neighborhood to another. For example, one neighborhood may be close to open farmland, while another neighborhood may be near a busy interstate highway and an airport (figure 5). The land use context around a neighborhood may be a mixture of uses, too. For example, a
neighborhood may be bordered by a national forest on one side and a busy industrial area on another.

Two aerial photos showing land use. One is in a city area and the other in a more suburban area with a mountain and body of water near the neighborhoods. — **Figure 5**. Look at the photos. What similarities and differences do you notice?

Most wildlife species are present in many land use contexts, from forests to farms to factory areas and even yards. The land use context of the areas around people’s yards may relate to the variety of species able to live in or pass through yards (see Thinking About the Environment). The scientists in this study were interested in mammal species that live in and around residential yards. They wanted to know how the land use context around residential yards affects the number and type of mammals present in the yards.

In addition to large-scale features like how the land is used around a yard, other smaller scale features may influence the number and types of wildlife in yards (table 1).

Table 1

Table 1. Human-provided resources for wildlife in residential yards
Intentional	Unintentional
Bird feeders	Garbage cans
Bird baths	Chicken coops with eggs
Bat boxes	Vegetable and fruit gardens
Gardens palnted for animals	Pet food left outside

The individual features in yards can provide habitat for wildlife species, including mammals. For example, trees and other plants in yards can be used by wildlife for food and shelter. Humans may intentionally provide resources for wildlife, like hanging bird feeders and bat boxes or planting a pollinator garden (figure 6). Humans may also unintentionally provide resources for wildlife, like placing kitchen trash outside where raccoons or bears can eat it.

A bird feeder hanging from a tree — **Figure 6**. This bird feeder is a resource that is intentionally provided by a human.

While there may be many available resources for mammals in residential yards, disturbances are also present. Disturbances are things that may scare mammals away or make it difficult for them to use the resources in a yard, such as distracting lights or fences that block their movement. Another disturbance is the presence of domestic animals. Domestic animals, like cats and dogs, live with or are taken care of by humans. Domestic species can scare or hurt wild animals, including mammals. Therefore, the scientists in this study also wanted to know how these types of resources and disturbances affect the number and type of mammals present in the yards.

Reflection Section

Methods

The study took place in 36 yards in and around the city of Springfield, Massachusetts, in urban, suburban, and rural neighborhoods (figure 7). Scientists randomly selected the yards to use in the study. The yards were at least 250 meters apart, and most were over 1 kilometer apart. Two cameras were placed in each yard. The cameras took photos for 8 days twice a year, in the late spring and then again in the late summer, from 2016 through 2018.

A map of Massachusetts — **Figure 7**. This map shows the location of Springfield, MA.

The scientists used motion-sensing cameras, called camera traps, to take pictures of mammals in yards. Camera traps are a common tool for scientists who study mammals. Camera traps collect data on mammals that are hard to observe in person. Scientists often collect data with cameras because a lot of mammals are nocturnal or hide when humans are around. The camera trap will take photos when a mammal moves in front of the camera, allowing scientists to collect data when humans are not there.

Number Crunch

In each yard, the two cameras were mounted on 1-meter-tall garden stakes. Scientists placed one camera about 2.5 meters from a bird nest box and focused it on the nest box (figure 8). They focused this camera on the nest box to capture photos of any mammals trying to eat the birds or eggs that were in the nest box. Scientists placed a second camera at least 10 meters away from the bird nest box and facing a natural area of the yard. This second camera was pointed towards an area in the yard where the scientists thought mammals might be walking.

A bird box and a camera trap set up by a tree — **Figure 8**. What do you notice about where the camera trap is in relation to the bird box?

Did You Know?

Scientists can do more than one study at a time based upon a single study design. In this study about mammals, the scientists were also collecting data on house wrens using the nest boxes. House wrens are small birds that are common in North America. The scientists were studying how land use context impacts house wrens in the same yards where they were studying mammals.

Two images side by side. One is a birds nest with baby birds and the other is a birds nest with eggs.

Scientists randomly selected yards with a variety of land use contexts that ranged from more densely populated suburban areas to sparsely populated rural areas. The land use contexts around the yards included a mix of homes, agricultural areas, recreational areas like parks or playgrounds, and forested areas.

The scientists also collected data about the habitat in the yards. The people who owned the yards took care of their yards in different ways. Some yards had open lawns while others had trees, shrubs, wild grasses, or gardens (figure 9). The scientists collected data to determine the types of plants in each yard. The scientists also collected data on the resources humans could be providing to wild mammals as well as the disturbances in each yard.

A house is behind a field full of weeds and flowers — **Figure 9**. This house has a large front yard with an open field next to it.

After the scientists removed the cameras from the yards, they used a computer program to look at every picture and identify the species of the mammals in the pictures. The program stored the number of photos of each mammal species in each yard. Next, the scientists asked a college student to look at each picture to identify the mammal. Then a second student looked at the picture again to identify the mammal. If the two students did not agree, a third expert would break the tie and decide who was correct. The scientists did this to be sure that the identification was accurate. Once they had identified the mammal species in every photo, they analyzed the results.

Reflection Section

How Do You Use A Camera Trap?

When deciding where to put a camera trap, scientists usually look for a location within their study area that a mammal would likely walk through. For example, sometimes there is a clear path that mammals are already using. Locations that have plants or places for the mammal to walk while still being hidden are often good places to point the camera. Look closely. Can you find the camera trap in these photos?

A camera trap on a farm a camera trap set up in front of a bird box

Another clear sign of a mammal is the presence of tracks or scat. Tracks are the mammal’s paw print in the soil or snow. Scat is what scientists call a mammal’s fecal droppings. The presence of scat or tracks in an area is a good sign that the mammal may walk through the area again.

animal tracks in snow

animal track in mud

Some mammals are hard to find using a camera trap. It may be weeks or months before a more elusive mammal will walk in front of a camera trap in wild areas. To help detect an elusive mammal, the scientists will sometimes use bait, like food or something that smells strongly, to attract the mammal. Not all camera traps use bait, though. Sometimes scientists want to study many species or learn about which species live in a study area. This kind of study does not require a camera trap with bait. The scientists in this study used camera traps that were not baited.

A camera trap on a wood pole set up in a forested area

Findings

The camera traps took photos of 14 different wild mammal species and 2 domestic species (table 2). The scientists found that the land use context of the yards seemed to have more of an influence on the number of different mammal species in the yards than the small-scale lawn features did.

Table 2

Table 2. The table shows all the mammal species detected by the camera traps in 36 yards.
Species	Total Detections	Percentage of yards where mammal species were detected
Eastern gray squirrel	1,248	94%
Eastern chipmunk	1,019	89%
Domestic cat	223	72%
Rabbit species	223	78%
Domestic dog	196	36%
Common Raccoon	111	64%
Virginia opossum	102	67%
Groundhog	90	22%
Striped skunk	79	72%
Red fox	28	33%
Mice/vole species	24	31%
Gray fox	19	31%
White-tailed deer	19	22%
American red squirrel	13	11%
Coyote	6	17%
Black bear	5	11%

Yards that were in a more suburban land use context had a greater variety of mammal species than yards that were in more rural or urban land use contexts. The scientists noted that the suburban yards had more forest and agricultural land nearby, whereas urban land had more industrial, commercial, and residential land nearby.

Scientists found that certain species were more likely to be found in yards with a certain land use context. For example, eastern gray squirrels, opossums, and red squirrels were more likely to be found in yards that were near more developed urban areas. Black bears, coyotes, gray foxes, skunks, and white-tailed deer were more likely to be found in yards in more rural areas. In suburban areas, species like eastern chipmunks, groundhogs, rabbits, and raccoons were common, but other species from urban and rural areas were also detected (figure 10). Specific features in the yards did not seem to influence the variety of species in a yard.

An illustration showing where different mammals are found in an urban, suburban, and rural areas — **Figure 10**. This illustration shows which species were most likely to be found in urban, suburban, or rural areas. However, many species in urban and rural areas were also present in suburban yards.

Did You Know?

Scientists did not find clear data that the presence of domestic cats and dogs impacted the overall number of mammal species in yards. However, some data indicated that domestic cats may influence which mammal species are present in yards.

A striped cat in a tree

For example, species that cats prey on, like eastern gray squirrels, were less likely to be in yards with cats. Also, species that prey on cats, like gray foxes, were more likely to be found in yards with cats. Scientists think the impact of domestic cats in these ecosystems should be studied more.

A grey cat in a bush outside

Reflection Section

Discussion

Scientists found that suburban yards had a greater variety of mammal species than yards in more urban or rural areas. Suburban yards tended to have a greater variety of surrounding land use contexts; these yards tended to be near both more developed areas, like other neighborhoods or shopping areas, and more natural areas, like parks or forests.

Scientists also noted that land use context may be more important than small-scale yard features because of the location of the study. The average size of residential yards in western Massachusetts is smaller than the ranges of many of the medium and large-size mammals in the area, like raccoons and coyotes. Even mammals that are found more often in natural areas may have to cross into more developed areas to seek food or shelter. This crossing into more developed areas may be due to habitat fragmentation. Mammals may use suburban yards to travel between more natural or rural areas.

On a large scale, land can be managed to protect the habitats of these mammals. Communities can make decisions about how to develop the land to meet the needs of both people and wildlife. If habitat fragmentation occurs, communities can also work to create and maintain green spaces that link to other green spaces so mammals and other wildlife can travel throughout an ecosystem to find food, water, and shelter (figure 11).

Green space next to a major road. There is a body of water and a lot of trees outside of a suburban area. — **Figure 11**. Green space can provide a way for mammals and other wildlife to travel throughout an ecosystem.

However, the scientists also point out that small-scale actions in individual yards can be helpful to mammals, especially in suburban yards since those yards have the greatest variety of mammal species. The scientists point out that residential areas, once developed, tend to stay residential. Therefore, yards are a relatively stable feature of local ecosystems, and yards are generally controlled by their owners. Residents in suburban areas can manage their own yards as habitats for wildlife in a variety of ways, like keeping and caring for large, mature trees in the yard or keeping cats inside so they don’t prey on wildlife. Many of the mammal species in the study were too small for the scientists to identify in the camera trap photos (figure 12). The scientists suggest that future researchers utilize live-trapping techniques to identify small mammals that may be interacting with domestic cats. Live-trapping techniques allow qualified professionals to safely capture an animal and then release it without harming the animal.

A mouse in a tree — **Figure 12**. Small mammals, such as mice and voles, are difficult for scientists to identify using the camera trap.

The scientists also suggest that future research projects should take place across multiple seasons throughout the year. Data from all four seasons of the year could help scientists better understand mammal patterns in residential areas and therefore how to support mammal species in residential yards.

Reflection Section

Adapted from Grade, Aaron M.; Warren, Paige S.; Lerman, Susannah B. 2022. Managing yards for mammals: mammal species richness peaks in the suburbs. Landscape and Urban Planning. 220(5): 104337. https://doi.org/10.1016/j.landurbplan.2021.104337.

Photo credits: Article banner, figures 1 and 4B: Adobe Stock photos; Meet the Scientists: courtesy photos by Aaron Grade, Paige Warren, and Susannah Lerman; figures 2 and 12, bear and weasel tracks: U.S. Fish and Wildlife photos; figure 3: courtesy photo by Babs McDonald; figure 4A: Washington State Department of Transportation photo; figure 5A: USDA Forest Service photo by Andrew Avitt; figures 5B and 11, glossary banner: USDA Forest Service photos by Preston Keres; figure 6, Did You Know? top cat: courtesy photos by Emlyn McKinney; figure 7: FIND Outdoors map by Leslie Shaw Design; figure 8, Did You Know?, camera traps: courtesy photos by Aaron Grade; figure 9: FIND Outdoors photo by Jessica Nickelsen; figure 10: FIND Outdoors illustration by Stephanie Pfeiffer Rossow; Did You Know? bottom cat: courtesy photo by Michelle Andrews

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Lights, Camera, Tracks! - Vol. 1 No. 28

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Meet the Scientists

Introduces students to the scientists who did the research. This section may be used in a discussion about careers in science.
What Kinds of Scientist Did This Research?

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Thinking About Science

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Describes the method the scientists used to collect and analyze their data.
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Describes the results of the analysis. Addresses the findings and places them into the context of the original problem or question.
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Number Crunches

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