Preliminary Analysis of the Effects of Non-target Supplemental

Georgia Journal of Science Georgia Journal of Science

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Article 13

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Preliminary Analysis of the Effects of Non-target Supplemental Preliminary Analysis of the Effects of Non-target Supplemental

Feeding on Camera Trap Captures of Small Mammals in Central Feeding on Camera Trap Captures of Small Mammals in Central

Georgia Georgia

Raena McCown

University of Georgia

, [email protected]

Travis Cunningham

Georgia College & State University

, [email protected]

Alfred J. Mead

Georgia College & State University

, [email protected]

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Recommended Citation Recommended Citation

McCown, Raena; Cunningham, Travis; and Mead, Alfred J. (2022) "Preliminary Analysis of the Effects of

Non-target Supplemental Feeding on Camera Trap Captures of Small Mammals in Central Georgia,"

Georgia Journal of Science

, Vol. 80, No. 2, Article 13.

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Preliminary Analysis of the Effects of Non-target Supplemental Feeding on Preliminary Analysis of the Effects of Non-target Supplemental Feeding on

Camera Trap Captures of Small Mammals in Central Georgia Camera Trap Captures of Small Mammals in Central Georgia

Acknowledgements Acknowledgements

A special thanks to Heidi Mead at Georgia College for her assistance with photography and James Mead

for the aerial drone photography. This manuscript bene>ted from critical reviews by Heidi Mead, Dennis

Parmley, Haley Marshall, and two anonymous reviewers. This research was supported by Faculty

Development Funds from the College of Arts and Sciences, Georgia College & State University.

This research articles is available in Georgia Journal of Science: https://digitalcommons.gaacademy.org/gjs/vol80/

iss2/13

PRELIMINARY ANALYSIS OF THE EFFECTS OF NON-TARGET

SUPPLEMENTAL FEEDING ON CAMERA TRAP CAPTURES OF SMALL

MAMMALS IN CENTRAL GEORGIA

Raena McCown

1,2

Travis Cunningham

Alfred J. Mead

College of Agriculture and Environmental Sciences

University of Georgia

Athens, GA 30602

Department of Biological and Environmental Sciences

Georgia College & State University

Milledgeville, GA 31061

*corresponding author

[email protected]

ABSTRACT

Supplemental bird feeding is a widespread hobby throughout western

culture. Although it brings joy to many people, bird feeding has been shown

to have potentially negative effects on local bird populations and small

mammalian species. To study the differences in local occurrence of native

small mammalian species around bird feeders and in more distant settings,

six camera traps were placed in a rural residential area in Putnam County,

Georgia. Three cameras were placed facing bird feeders and three placed a

minimum of 60 m away from the feeders. Species presence was recorded

three days a week from 12:00 am Monday to 12:00 am Thursday between

11 November 2019 and 29 January 2020. We recorded 5,073 images of

mammals during the 36 days: gray squirrels (4,264), eastern chipmunks

(458), raccoons (113), Virginia opossums (65), domestic cats (54), white-

tailed deer (36), gray foxes (35), field mice (22), armadillos (11), eastern

cottontail rabbits (11), and domestic dogs (4). Pair-wise t-tests indicate a

greater frequency of image-captures of gray squirrels, chipmunks, raccoons,

opossums and cats near the feeders compared to the area away from the

feeders. Foxes and deer were imaged more frequently in the area away from

the feeders. Not only do bird feeders contribute to a higher visitation

frequency in certain species such as gray squirrels and raccoons, species

known to depredate bird nests, the elevated densities of birds and mammals

in the area also attract more predators such as domestic/feral cats. This

study suggests that future research is needed to investigate the effects of

bird feeders on the behavior of small mammals and the magnitude to which

excess predation at supplemental bird feeders affects the community

structure.

Keywords: supplemental feeding, small mammals, camera trap capture

frequency, Georgia

McCown et al.: Effects of Supplemental Feeding on Small Mammals

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INTRODUCTION

Recreational bird watching is a common pastime throughout the United States.

According to the most recent data from the U.S. Fish & Wildlife Service (Carver 2019),

there were 45 million bird watchers (birders) in the U.S. in 2016, with 39 million of these

birders enjoying the activity around their homes. Many birders enhance their chances of

seeing birds by using supplemental bird feeding stations. In the 2016 survey, birders

reported spending $8,874,978,000 on wildlife-watching equipment which included bird

food, bird feeders, bird houses, bird baths, binoculars, cameras, and field guides. Besides

the recreational value, backyard bird feeding also offers unique research opportunities,

and could lead to an enhanced societal conservation ethic (Jones and Reynolds 2008).

Although it brings joy to many people and plays a vital role in avian conservation efforts

(Ewen et al. 2014), there are negative effects associated with supplemental bird feeding

(Jones and Reynolds 2008). Supplemental bird feeding has been linked to increased local

abundance of non-native bird species resulting in the restructuring of urban avian

communities to the detriment of native species (Galbraith et al. 2015), and a higher

prevalence of infectious diseases (Wilcoxen et al. 2015). Positive effects include improved

body condition and innate immune defense (Wilcoxen et al. 2015), increased survival of

juvenile and adult migratory birds (Seward et al. 2013), extended breeding season and

increased clutch size (Bonnington et al. 2014, Boutin 1990, Prevedello et al. 2013), and in

some cases, a long term increase in bird diversity in some communities (Plummer et al.

2019). In many instances, actively feeding birds displace a portion of the supplemental

feed from feeders onto the ground below where many ground feeding avian species make

use of the displaced seeds. However, once on the ground, small mammals have access to

the feed (Reed and Bonter 2018) and actively compete with birds for the resource

(Bonnington et al. 2014). Some small mammals such as gray squirrels (Sciurus

carolinensis) and raccoons (Procyon lotor), attracted to an area by the available grain,

may influence local avian populations through nest predation (Bonnington et al. 2014,

DeGregorio et al. 2016, Moller 1983).

Small mammal population density is often food supply limited (Boutin 1990). Food

supplementation increases small mammal density through higher rates of reproduction,

survival, or immigration (Reed and Bonter 2018, Prevedello et al. 2013). However, this

result is not uniform in all environments. In rural mature hardwood forests, fox squirrels

(Sciurus niger) and gray squirrels displayed no noticeable benefit from supplemental

shelled corn during winter months (Havera and Nixon 1980). When provided with

supplemental food, eastern chipmunk (Tamias striatus) home range size decreased and

population density increased (Mares et al. 1976). Red squirrels (Tamiasciurus

hudsonicus) displayed a 3-4 times density increase when supplied with supplemental

food (Sullivan 1990). Other small mammals such as raccoons (Procyon lotor) displayed

smaller, more stable home ranges and greater local density when presented with

accessible supplemental food (Prange et al. 2004, Reed and Bonter 2018).

Higher densities of rodents around feeding stations also increased disease

transmission (Forbes et al. 2015). Compartmental models of disease dynamics suggest

that supplemental feeding may maximize pathogen prevalence in a local population

(Becker and Hall 2014). Parasites take advantage of the higher densities and spread

throughout susceptible hosts congregating at supplemental feeders (Lambert and

Demarais 2001). Concentrated food sources and a de-sensitivity to humans affects some

rodents in other ways. Gray squirrels, fox squirrels, red squirrels, and chipmunks in urban

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areas with supplemental feeding stations become less sensitive to predatory risks,

increasing predator-prey contact (Bowers and Breland 1996, Mares et al. 1976, McCleery

2009, Sullivan 1990, Uchida et al. 2016). Natural (avian raptors) and domestic (especially

cats [Felis catus]) predators take advantage of supplemental feeding areas and become a

limiting factor to small mammal population densities (Baker et al. 2003, Bowers and

Breland 1996, Prevedello et al. 2013).

Camera traps typically consist of digital trail cameras with passive infrared motion

sensors and built-in infrared nighttime illuminators. These cameras allow researchers to

monitor a species’ frequency of occurrence within an active camera’s visual range, day or

night. The validity of animal identification from camera trap photographs can be

questionable, especially when observed animals are relatively small and multiple similar

species from a given genus reside in the area (Meek et al. 2013). Correct identification

increases when the differences between the photographed animals are obvious. Most

small mammals are recognizable to genus or species but lack markings that allow the

identification of an individual organism. Therefore, a major assumption of camera trap

studies is the direct correlation between the frequency of images captured and the relative

local abundance. In the current study, digital trail cameras were employed in a rural

residential area to monitor the effects of an established supplemental bird feeding station

(20 years of continuous use) on camera capture frequency of mammals near the feeders

compared to nearby sites not immediately adjacent to the feeders.

MATERIALS & METHODS

The capture frequency of mammalian species was surveyed on a 0.77 hectare rural

residential lot in Putnam County, Georgia (Figure 1) using automatic camera traps. The

surrounding area consists of 0.40 to 2.83 hectare residential lots in a mature hardwood

forest bordering Lake Sinclair. The small residential area is bordered by approximately

250 hectare of managed timberland. The owners of the study property did not have pet

domestic cats, did not feed feral cats, and did not have free-ranging dogs (Canis

Figure 1. Aerial view of study area in Putnam County, Georgia showing the positions of camera traps

(stars) used in this study. Image covers approximately 0.77 hectare. Dashed line indicates position of dirt

access drive. Drone image by James Mead.

McCown et al.: Effects of Supplemental Feeding on Small Mammals

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familiaris). Six BlazeVideo® SL112 digital trail cameras with passive infrared motion

sensor and built-in infrared nighttime illuminator were positioned on the property. The

cameras were programmed to delay a minimum of 60 seconds between successive

triggers. Three cameras were placed one meter above the ground and angled slightly down

in areas a minimum of 60 m away from the bird feeders: along a dirt drive, near a natural

spring, and beneath large oak trees (Figure 1). Three cameras were placed around the

supplemental bird feeding station (Figure 1, 2). The supplemental bird feeding station

consisted of one suspended mixed birdseed feeder (Figure 2A; white proso millet

[Panicum miliaceum], milo [Sorghum bicolor], wheat [Triticum sp.], black oil sunflower

seed [Helianthus annus], cracked corn [Zea mays]), one suspended thistle seed feeder

(Figure 2B; Guizotia abyssinica), one suspended suet cake feeder (Figure 2G; rendered

beef suet, corn, white millet, oats [Avena sativa], sunflower meal), and one wooden post-

mounted black oil sunflower seed feeder (Figure 2C). The wooden post was climbable by

small mammals. One camera (Figure 2D, below bell) was mounted to capture images

beneath the suspended mixed birdseed feeder, another (Figure 2E, below green) was

mounted to capture images beneath the wooden post-mounted black oil sunflower seed

feeder, and the third (Figure 2F, high green) was mounted to capture images of the

wooden post and mounted black oil sunflower feeder.

Figure 2. Supplemental bird feeding station in a rural residential lot in Putnam County, Georgia. A)

suspended mixed birdseed feeder; B) suspended thistle seed feeder; C) black oil sunflower seed feeder

mounted on wooden post; D) trail camera (below bell) scanning under suspended mixed birdseed feeder;

E) trail camera (below green) scanning under mounted black oil sunflower seed feeder; F) trail camera (high

green) scanning wooden post and mounted black oil sunflower seed feeder; G) suspended suet cake feeder;

H) spilled seed on ground; I) bird bath. Photography by Heidi Mead.

The presence of mammals was recorded three days a week from 12:00 am Monday

to 12:00 am Thursday between 11 November 2019 and 29 January 2020, resulting in 36

days of observation. Every individual of each species in each image was tallied. On the

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occasion that a camera malfunctioned for the day, the lack of data was not included in the

statistical analyses. Pair-wise t-tests of the six camera stations were utilized to analyze the

statistical difference (α ≤ 0.05) in mean capture frequency for each species at each camera

location. Due to the overlapping fields of view for the cameras located near the bird

feeders (Figure 2), it is highly probable that, in some instances, individual animals were

captured on two cameras at the same time. It must be acknowledged that the total number

of captures is elevated due to this overlap.

RESULTS

During the 36-day study period, we recorded 5,073 mammals (Table I). Gray

squirrels were the most abundant taxon in both areas. Near the feeders, multiple squirrels

in the same image were common. The most abundant taxa near the feeders, following

gray squirrels, were chipmunks, raccoons, opossums (Didelphis virginiana), cats, mice

(most likely Peromyscus), Eastern cottontail rabbits (Sylvilagus floridanus), armadillos

(Dasypus novemcinctus), white-tailed deer (Odocoileus virginianus), and gray foxes

(Urocyon cinereoargenteus). No dogs were recorded near the feeders. The most

abundant taxa in the area not near the feeders, following gray squirrels, were deer (13 of

35 deer were photographed in one night, 22 January 2020), foxes, opossums, cats,

raccoons, armadillos, rabbits, dogs, and chipmunks. Mice were recorded only near the

feeders.

The pair-wise t-tests indicate a greater frequency of image-captures of gray

squirrels, chipmunks, raccoons, opossums, and cats near the feeders compared to the area

away from the feeders (Table II). Foxes and deer were imaged more frequently in the area

away from the feeders. For the cameras near the feeders, more photographs of cats and

Table I. Number of observations of each taxon at each camera in close proximity to a supplemental bird

feeding station (Feeder) and each camera not adjacent to the feeding station (Yard) in Putnam County,

Georgia. Sq = gray squirrel (Sciurus carolinensis), Ch = eastern chipmunk (Tamias striatus), Ra = raccoon

(Procyon lotor), Op = Virginia opossum (Didelphis virginiana), Ca = domestic/feral cat (Felis catus), De =

white-tailed deer (Odocoileus virginianus), Fx = gray fox (Urocyon cinereoargenteus), Mo = field mouse

(most likely Peromyscus), Ar = nine-banded armadillo (Dasypus novemcinctus), Rb = Eastern cottontail

rabbit (Sylvilagus floridanus), Dg = domestic dog (Canis familiaris).

Feeder Total

3898

455

100

High green

474

Below green

1592

394

Below bell

1832

Yard Total

366

Dirt drive

Natural spring

Large oaks

221

Survey Total

4264

458

113

McCown et al.: Effects of Supplemental Feeding on Small Mammals

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armadillos were captured by the below bell camera compared to the other two cameras.

More photographs were recorded by the below bell and below green cameras compared

to the high green camera. For the cameras located away from the feeders, gray squirrels

were more commonly photographed near the yard oaks, and opossums and cats were

more abundant at the oaks compared to the dirt drive and yard spring, respectively.

A difference in gray squirrel and chipmunk behavior was observed at the

supplemental feeders. Both species are typically active in the morning and evening in

natural settings (Koprowski 1994), but instead were active throughout the daylight hours

at the bird feeders. Some intraspecific antagonistic squirrel behavior was recorded at the

bird feeders (Figure 3). Even though there was a higher frequency of squirrels and

chipmunks around the feeders compared to the distant areas, the two taxa were rarely

photographed together. Additionally, there was evidence of predation events near the

feeders (Figure 4) during the study period, however no images of active predation were

captured.

Table II. Results of pair-wise two-tailed t-tests comparing the mean number of image-captures of each

taxon by each camera in Putnam County, Georgia. Significantly greater (p ≤ 0.05) mean values are denoted

for the left column variable compared to top row variable. Sq = gray squirrel (Sciurus carolinensis), Ch =

eastern chipmunk (Tamias striatus), Ra = raccoon (Procyon lotor), Op = Virginia opossum (Didelphis

virginiana), Ca = domestic/feral cat (Felis catus), De = white-tailed deer (Odocoileus virginianus), Fx =

gray fox (Urocyon cinereoargenteus), Ar = nine-banded armadillo (Dasypus novemcinctus).

High Green

Below Green

Below Bell

Dirt Drive

Yard Spring

Yard Oaks

High Green

n/a

Sq, Ch, Ra,

Sq, Ra

Below Green

Sq, Ch, Op

n/a

Sq, Ch, Ra,

Sq, Ch, Ra

Sq, Ch, Ra,

Below Bell

Sq, Ch, Ca,

Ca, Ar

n/a

Sq, Ch, Ra,

Op, Ca

Sq, Ch, Ca

Sq, Ch, Ra,

Ca, Ar

Dirt Drive

Fx, Ca

n/a

Yard Spring

Fx, De

n/a

Yard Oaks

Fx, Ca

Sq, Op

Sq, Ca

n/a

DISCUSSION

It was no surprise that more photographs of small mammals were recorded by the

cameras in close proximity to the supplement food source compared to cameras in more

natural settings. In particular, squirrels and chipmunks spent a greater amount of time

around the feeders. In this area, capture frequency was highest for the below bell and

below green cameras compared to the high green camera. Most small mammals were

utilizing the seeds on the ground rather than trying to gain seeds directly from the feeders.

Squirrels, chipmunks, raccoons, and opossums utilized the climbable wooden post and

were photographed on the high green feeder. The cats captured by the high green camera

were not on the high green feeder, but on the ground behind the feeder. The below bell

and below green totals were minimally different, and due to the positioning of these two

cameras, it is likely that they frequently captured the same animals. Mice were only

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photographed by the below green camera, likely due to the camera being positioned low

to the ground and pointing directly at the concentrated food source surrounded by plant

and rock cover. It is likely that the small size of the mouse was not sufficient to trigger the

other cameras if this species occurred in those fields of view. For the cameras away from

the feeders, the greater abundance of squirrels near the large oaks was expected due the

local concentration of acorns. The most significant finding of this study is the greater

frequency of cats near bird feeders. Since cats and foxes are not seed eating mammals, the

greater abundance of these species near (cats) and away (foxes) from the feeders suggests

additional concentrating factors.

Many mammalian taxa are commonly observed in and around residential yards

(Kays and Parsons 2014) due to the positive correlation between food availability and

population density (Boutin 1990). The greater abundance of gray squirrels and

chipmunks photographed at the supplemental bird feeding station in the current study

agrees with the findings of previous studies (Mares et al. 1976, Reed and Bonter 2018).

Within gray squirrel populations, intraspecific aggression is positively correlated and

wariness is negatively correlated with local density (Parker and Nilon 2008). Intraspecific

aggression may lead to a greater frequency of injury in this species (Bosch et al. 2016,

Moncrief et al. 2022). We captured images of apparent aggressive interactions between

squirrels below the bell feeder (Figure 3). Aggressive behavior by gray squirrels toward

chipmunks beneath the bell feeder was also observed, although we did not photograph

the interactions (A. Mead; personal observation). Even though gray squirrels (n = 3,898)

and chipmunks (n = 455) were the two most frequently observed taxa at the bird feeding

station, they were rarely photographed simultaneously. Reduced wariness in small

mammals increases the likelihood of predation, particularly by domestic cats (Loss et al.

2013). Elevated densities of gray squirrels and chipmunks also increase interspecific

interactions with birds and other small mammals. In addition to the direct competition

with birds for spilled seed, both taxa are known to predate bird eggs and nestlings (Bailey

1923, Cain et al. 2006). The observed elevated local abundance of gray squirrels and

chipmunks likely negatively affect passerines nesting in the study area (Cain et al. 2006,

Figure 3. Evidence of intraspecific aggressive behavior between gray squirrels (Sciurus carolinensis)

near a supplemental bird feeding station in a rural residential lot in Putnam County, Georgia.

McCown et al.: Effects of Supplemental Feeding on Small Mammals

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DeGregorio et al. 2016, Hanmer et al. 2016, Heske et al. 2001, Snyder 1982). Elevated

local abundances also increase the likelihood of disease and parasite transmission within

these species (Becker and Hall 2014, Forbes et al. 2015, Lambert and Demarais 2001).

Raccoons, opossums, and domestic cats were found in greater abundance near the

feeders, while gray foxes and deer were more abundant in distant areas. Raccoons have

been found in greater abundance around urban chicken coops (Kays and Parsons 2014)

and supplemental feeders used for ungulates (Lambert and Demarais 2001). Being

nocturnal omnivores, raccoons and opossums rarely compete directly with avian taxa for

spilled seed. However, in a review of mammalian bird nest predation, raccoons and

opossums were found to be the top two non-rodent predators (DeGregorio et al. 2016).

Large populations of free-ranging cats have been documented in many residential areas

(Elizondo and Loss 2016). The greater abundance of cats near the bird feeders in the

current study most likely negatively affects the local avian and small mammal populations

(Baker et al. 2003, Simpson et al. 2013). It is estimated that domestic cats, functioning as

both diurnal and nocturnal predators, kill 1.4–3.7 billion birds and 6.9–20.7 billion

mammals annually in the United States (Loss et al. 2013). Injury from domestic cat attack

is the leading cause of gray squirrel and chipmunk admission at wildlife rescue centers

(Levy et al. 2020, Loyd et al. 2017, Schenk 2017, Schenk and Souza 2014). Evidence of

predation below the bell feeder (Figure 4) was observed within the time window of this

study, but since it occurred during the latter part of the week when the cameras were not

actively recording, we did not capture an image and were unable to determine the identity

of the predators. Gray foxes and deer were the only taxa photographed more frequently

in the area away from the feeders. For gray foxes, this may suggest that bird feeding

stations do not concentrate prey species at the right time of day for this nocturnal

predator. Additionally, the relative lack of foxes near the bird feeders may be related to

this species’ avoidance of baited areas (Rexford 1961). The relative lack of deer near the

bird feeders may be a result of the close proximity of the feeders to the house.

Figure 4. Evidence of predation events near a supplemental bird feeding station in a rural residential lot

in Putnam County, Georgia. A) feather piles (arrows) beneath a suspended mixed birdseed feeder, digital

trail camera in the background; B) feather pile (arrow) underneath a bush approximately 4.0 meters from

the suspended mixed birdseed feeder. Photography by Heidi Mead.

Supplemental bird feeding stations benefit avian species by providing nutrition

that may otherwise be limited in a local area. However, the greater frequencies of

occurrence of gray squirrels, chipmunks, raccoons, opossums, and domestic cats around

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feeding stations are potentially harmful for avian species through direct competition for

seeds, nest depredation, and elevated predation. Future studies should determine if

feeders with spill protector saucers decrease the frequency of spilled seed, and in turn

decrease the abundance of ground foraging birds and the number of gray squirrels,

chipmunks, raccoons, opossums, and domestic cats at feeding stations. Additional

research is needed to investigate the effects of spilled seed from bird feeders on the

intraspecific and interspecific behavior of small mammals as well as the magnitude to

which excess predation at supplemental bird feeders affects the community structure.

ACKNOWLEDGEMENTS

A special thanks to Heidi Mead at Georgia College for her assistance with

photography and James Mead for the aerial drone photography. This manuscript

benefited from critical reviews by Heidi Mead, Dennis Parmley, Haley Marshall, and two

anonymous reviewers. This research was supported by Faculty Development Funds from

the College of Arts and Sciences, Georgia College & State University.

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