Diets of Black Vultures and Turkey Vultures in Coastal South Carolina, USA with a Review of Species' Dietary Information

Abstract

Food availability resulting from anthropogenic land-use changes may have contributed to the recent increase of Cathartes aura (Turkey Vulture) and Coragyps atratus (Black Vulture) populations. We assessed anthropogenic contributions to diets of these species
by analyzing 176 pellets collected from communal roosts in coastal South Carolina. To provide further insight into diets, we conducted a literature review of pellet-based studies for both species. Our pellet analyses demonstrated consumption of 12 mammal species with
Odocoileus virginianus (White-tailed Deer) as the primary food item, present in 65% of samples and constituting 35% average percent volume in pellets. Mephitis mephitis (Striped Skunk) and Procyon lotor (Raccoon) were also commonly consumed. Presence of anthropogenic items in 47% of pellets indicated substantial garbage consumption. Our review consisted of 14 studies and revealed wide variability in diet across study sites, with large mammals (>15 kg) typically comprising the majority of species consumed. We suggest that increasing deer populations provide an important source of carrion for vultures in this area and likely throughout eastern North America. Ungulate populations, roadkill, and garbage appear to contribute considerably to Turkey Vulture and Black Vulture diets. As such, mitigation of human–vulture conflict will require effective garbage and roadkill management as Turkey Vulture and Black Vulture populations increasingly expand.

Full text

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J.E. Hill, A.E. Holland, L.K. Brohl, B.M. Kluever, M.B. Pfeiffer, T.L. DeVault, and J.L. Belant
2022 Vol. 21, No. 1
SOUTHEASTERN NATURALIST
2022 21(1):11–27
Diets of Black Vultures and Turkey Vultures in Coastal
South Carolina, USA with a Review of Species’ Dietary
Information
Jacob E. Hill1,2,*, Amanda E. Holland2, Lisa K. Brohl3, Bryan M. Kluever4,
Morgan B. Pfeiffer5, Travis L. DeVault1, and Jerrold L. Belant2
Abstract - Food availability resulting from anthropogenic land-use changes may have
contributed to the recent increase of Cathartes aura (Turkey Vulture) and Coragyps atratus
(Black Vulture) populations. We assessed anthropogenic contributions to diets of these spe-
cies by analyzing 176 pellets collected from communal roosts in coastal South Carolina. To
provide further insight into diets, we conducted a literature review of pellet-based studies
for both species. Our pellet analyses demonstrated consumption of 12 mammal species with
Odocoileus virginianus (White-tailed Deer) as the primary food item, present in 65% of
samples and constituting 35% average percent volume in pellets. Mephitis mephitis (Striped
Skunk) and Procyon lotor (Raccoon) were also commonly consumed. Presence of anthro-
pogenic items in 47% of pellets indicated substantial garbage consumption. Our review
consisted of 14 studies and revealed wide variability in diet across study sites, with large
mammals (>15 kg) typically comprising the majority of species consumed. We suggest that
increasing deer populations provide an important source of carrion for vultures in this area
and likely throughout eastern North America. Ungulate populations, roadkill, and garbage
appear to contribute considerably to Turkey Vulture and Black Vulture diets. As such, miti-
gation of human–vulture conict will require effective garbage and roadkill management as
Turkey Vulture and Black Vulture populations increasingly expand.
Introduction
The acquisition of food plays a substantial role in the ecology and life history of
birds. The quantity and condition of offspring, for example, can be inuenced by
diet quality, as can an individual’s mating potential (McGlothlin et al. 2007, Rutz
et al. 2006). Greater food abundance may lead to population increases in some
species, and inter- and intraspecic social dynamics can be altered by the distribu-
tion of food (Blake and Loiselle 1991, Cortes-Avizanda, et al. 2011). Furthermore,
food availability has been deemed the primary driver of avian home-range ecology
(Rolando 2002). The availability of food may thus have impacts across multiple
1University of Georgia, Savannah River Ecology Laboratory, PO Drawer E, Aiken, SC
29802. 2Global Wildlife Conservation Center, State University of New York College of
Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210. 3Lake Erie
Islands Conservancy, P.O. Box 461, Put-in-Bay, OH 43456. 4United States Department of
Agriculture, Wildlife Services, National Wildlife Research Center, Florida Field Station,
2820 East University Avenue, Gainesville, FL 32641. 5United States Department of Ag-
riculture, Wildlife Services, National Wildlife Research Center, Ohio Field Station, 6100
Columbus Avenue, Sandusky, OH 44870. *Corresponding author - jearl.hill98@gmail.com.
Manuscript Editor: Roger Applegate

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levels of the ecological avian hierarchy from inuences on individual animals to
multispecies interactions (Cortes-Avizanda et al. 2011).
Considering the myriad impacts of food on avian ecology, there is consider-
able potential for humans to inuence birds via alterations in food distribution and
abundance. Habitat degradation, for instance, can cause declines in avian species
that have specialized diets due to decreased food availability (Morelli et al. 2021).
Conversely, some birds may benet from an increase in food provided by humans.
Cathartes aura L. (Turkey Vulture) and Coragyps atratus (Bechstein) (Black Vul-
ture ) are 2 species that have ourished over the past half century concurrent with
expanding human development, and an increase in food availability has been postu-
lated as one of the ecological drivers. The loss of apex predators in much of North
America may have led to higher populations of ungulates, resulting in greater car-
rion availability (Kiff 2000). Simultaneously, an increasing road network has likely
increased the availability of carrion via roadkill, which vultures consume (Hill et al.
2018, Kiff 2000). Additionally, both species forage extensively on anthropogenic
food sources such as human garbage and livestock carcasses (Humphrey et al. 2004,
Kluever et al. 2020, Novaes and Cintra 2015).
Scavenging by vultures is an important ecosystem service because it limits the
spread of disease and controls populations of scavenging pest species (DeVault et
al. 2016, Lambertucci et al. 2021). However, when they occur at high densities in
close proximity to people, vultures can cause problems such as property damage,
aircraft collisions, and human health concerns (Kluever et al. 2020, Lowney 1999).
As a result, the increasing population sizes and geographic ranges of both species
have coincided with a rise in the frequency of human–vulture conicts (Blackwell
et al. 2007, Kluever et al. 2020).
Despite the growing prevalence of both species, there remain unresolved ques-
tions regarding basic aspects of their ecology, such as detailed dietary information
(Avery et al. 2006). Vulture diets have important ramications for management, as
carrion availability is a major factor inuencing vulture presence (Kelly et al. 2007,
López-López et al. 2014, Rolando 2002). Vultures alter space use in accordance
with carrion availability and make repeated movements to sites where carrion is
reliably available (Cortés-Avizanda et al. 2012, López-López et al. 2014). Diets of
vultures can vary substantially across their geographic ranges, necessitating site-
specic investigations (Blázquez et al. 2016, Kelly et al. 2007).
Understanding the diets of both species may help to determine why vultures are
locally abundant and facilitate elimination of food items to disperse vultures when
desirable. Furthermore, knowledge of dietary information is vital to understanding
how vultures interact with human settlement and their functional roles in anthro-
pogenically modied landscapes. Such understanding will become increasingly
pertinent as the expanding ranges of both vulture species will likely precipitate
greater intermingling of vultures and people. Further, given the global endangered
conservation status for vultures as a group, the diets of vultures in stable popula-
tions may reveal patterns important for conservation (Ogada et al. 2012).

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After feeding, vultures regurgitate pellets containing indigestible parts of their
food such as bones, teeth, hair, and feathers (Houston et al. 2007). Analysis of
pellets can provide information on vulture diets and is one of the most commonly
employed methods to study the diets of birds of prey (Ballejo et al. 2018). Pellet
analysis may be biased by differences in digestibility of prey items (Litvaitis et al.
1994). However, vulture pellets contain primarily hair, and pellet analysis is reli-
able for diet estimation given knowledge of local fauna, reference collections for
comparisons, and the use of microscopy (Ballejo et al. 2018, Real 1996). Addition-
ally, pellet analysis has the advantage of being relatively inexpensive, and large
proportions of the population can be sampled with minimal disturbance to animals
(DeVault and Washburn 2013).
To address the paucity of data regarding vulture diets, we collected pellets from
mixed roosts of Turkey Vultures and Black Vultures in the coastal southeastern
United States, an area where diet information is currently lacking and human–vul-
ture conicts are increasing (Kluever et al. 2020). We examined seasonal variation
in diet composition, as well as spatial differences across roosts located on 3 proxi-
mate South Carolina sea islands. Additionally, we conducted a literature review
of diets of both species based on pellet analysis to provide a more comprehensive
understanding of the breadth of species’ diets as well as geographic variation in
dietary composition.
Methods
Field-site description
We conducted this study in Beaufort County, located in the low country salt
marsh region of South Carolina (32.418°N, 80.640°W; Fig. 1). The resident popu-
lation of Beaufort County is ~186,000, but tourism is a major part of the local
economy, and the annual number of visitors exceeds 3 million (Carey and Salazar
2017, US Census Bureau 2021). The coastline of this area is characterized by a
chain of land masses known as sea islands, separated from the mainland by marshes
and tidal creeks (Zeigler 1959). Mean annual temperature is 19.55 °C and mean
annual precipitation is 121.51 cm (NOAA 2021). Based on data from the National
Land Cover Database (Yang et al. 2018), predominate land-cover types in the area
include open water (33%), wetlands (33%), forest (21%), developed (9%), and ag-
riculture (3%). The area has a year-round population of Turkey Vultures and Black
Vultures (Walter et al. 2012).
Pellet collection and lab analysis
We collected pellets from 4 roosts across 3 sea islands during January–Au-
gust 2020: 1 on St. Helena Island, 1 on Lady’s Island and 2 on Port Royal Island
(Fig. 1). The roosts were communal Black Vulture and Turkey Vulture roosts on
communication or water towers. We surveyed the study area by vehicle near dusk
and looked for vultures returning to roosts to identify roost locations. The height
of these structures was well above buildings and tree lines, which facilitated visual
detections of vultures. Additionally, these structures spatially constrained vultures,
which aided collection of pellets beneath roosts.

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In the early evening, 12–16 hr before the initiation of a sampling trip, we placed
a plastic tarp under the roost. The combination of placing the tarp before most
vultures returned to roosts in the evening with vultures’ propensity to roost at the
highest points of the structures resulted in minimal disturbance to birds; we did not
observe birds ushing from the roost as a result of our eld efforts. We gathered
pellets from the tarp the next day such that each sample had been deposited less
than 24 hours prior to collection. We took all pellets available across the tarp area,
obtaining an average of 5.9 pellets (min–max = 1–18 pellets) per sampling trip
across the 30 sampling trips (Table 1). We aimed for an even temporal distribution
of sampling trips over the study period for each roost, but our ability to sample sites
was sometimes constrained by personnel limitations and site access.
Each pellet was placed in a plastic tube and stored in a freezer until analysis. We
soaked samples overnight in sealed jars to loosen the material and dissected them in
a glass dish for analysis. We made hair identications following Stains (1958) and
Cothran et al. (1991), as well as direct comparison with specimens from the col-
lections at the Lake Erie Islands Nature and Wildlife Center (Put-in-Bay, OH) and
the personal collection of Glen Bernhardt (Norwalk, OH). We made initial coarse
identications using physical characteristics of hairs under a 10-35x dissecting
Figure 1. Locations of 4 communal Black Vulture and Turkey Vulture roosts in coastal
South Carolina, from which pellets were collected in 2020.

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microscope (Stemi D4; Zeiss, Oberkochen, Germany). We veried dentications
by comparing individual hairs to known samples using a 40-1000x binocular com-
parison compound microscope (Primo Star; Zeiss).
Statistical analysis
We reported the frequency of each item (number of pellets containing the item)
documented across the entire set of samples. Many items such as rocks and soil
were probably ingested for reasons other than energy intake. Therefore, we also
calculated a modied estimate of average percent volume, dened as the proportion
of each prey item from each sample divided by the total amount of vertebrate mat-
ter consumed after removing large structures such as bones and claws × 100 (Kelly
et al. 2007). We excluded feathers from these estimates because we were unable to
identify them to species and most were probably incidentally ingested vulture down
Table 1. Number of pellets (n = 176) collected in 2020 from communal Black Vulture and Turkey
Vulture roosts in South Carolina, on each sampling trip (n = 30).
Date Island Pellets collected
14 January 20 Port Royal 12
25 January 20 Lady's 8
28 February 20 Lady's 5
19 March 20 Port Royal 3
27 March 20 Lady's 3
31 March 20 St. Helena 15
16 May 20 Port Royal 2
2 June 20 St. Helena 1
3 June 20 St. Helena 1
4 June 20 St. Helena 1
10 June 20 Lady's 1
10 June 20 St. Helena 4
12 June 20 Lady's 5
13 June 20 Lady's 1
13 June 20 St. Helena 18
14 June 20 St. Helena 1
16 June 20 Lady's 8
7 July 20 Lady's 1
9 July 20 Lady's 3
12 July 20 Lady's 7
12 July 20 St. Helena 13
17 July 20 Lady's 4
17 July 20 St. Helena 13
20 July 20 Lady's 1
20 July 20 St. Helena 1
23 July 20 Port Royal 3
27 July 20 Port Royal 6
27 July 20 St. Helena 14
1 August 20 Port Royal 17
1 August 20 St. Helena 4
Total 176

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(Kelly et al. 2007). In addition to percent volume at the pellet level, we calculated
an overall percent volume for each prey item from all pellets combined.
We examined changes in consumption of the 3 most common prey items
(Odocoileus virginianus (Zimmerman) [White-tailed Deer], Procyon lotor (L.)
[Raccoon], and Mephitis mephitis Schreber [Striped Skunk]) as a function of roost
location and season by constructing 2 sets of models using package stats in Program
R version 4.0.4 (R Core Team 2020). In the rst set, we compared the logit-trans-
formed proportion (derived from modied percent volume) of each prey species
in every sample as a response variable using linear models. In the second set of
models, we compared presence/absence of the prey species in every sample using
a generalized linear model with binomial distribution. In each model, we included
roost location (1 of the 3 islands) and season as factors. We combined winter and
spring (January–March) due to low sample sizes, resulting in 2 seasons for analysis:
winter/spring and summer (May–August). We also combined the 2 roosts from Port
Royal Island due to their proximity (2.3 km apart), for a total of 3 roost locations.
We calculated the Akaike’s information criterion corrected for sample size (AICc)
for each model (4 total possible models) and ranked models based on the differ-
ence in AICc values between each model and that with the lowest AICc (ΔAICc). We
averaged parameter estimates among models with ΔAICc ≤ 2 and calculated 85%
condence intervals (Arnold 2010, Burnham and Anderson 2002). If roost location
was a signicant parameter, we calculated pairwise comparisons between islands
with Tukey’s adjustment and α = 0.05 to determine differences using the package
‘emmeans’ (Lenth et al. 2018).
Literature Review
We obtained studies of the diets of Black Vultures and Turkey Vultures using
Web of Science, BioOne, and Google Scholar by searching entire documents for
combinations of the terms “pellet” and “diet” with each of the following terms:
“Turkey Vulture”, “Black Vulture”, “Cathartes aura”, and “Coragyps atratus”. We
only included studies that used pellets for dietary analysis; these provide greater
information on the breadth of diets than observations at carcasses, many of which
are placed by the researchers themselves for experimental purposes. We limited our
analysis to the rst 300 results sorted by relevance for our Google Scholar search
(Haddaway et al. 2015).
For every study, we documented the species from which pellets were collected
and the location of the study site. We recorded the frequency of occurrence in pel-
lets for every species documented because this was consistently reported whereas
percent volume was not. We tallied the presence of every food item across studies to
examine its prevalence. We also were interested in examining the relative contribu-
tions of mammals of different size classes to vulture diets, so we categorized every
mammal species consumed as either small (<1 kg), medium (1–15 kg), or large
(>15 kg). Vultures may scavenge carcasses across these size categories differen-
tially due to differences in detectability and carrion provided (Turner et al. 2017). It
was not possible to calculate contributions by only adding frequencies within each

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size class because they summed to greater than 1 due to pellets containing remains
from multiple species. We therefore calculated a modied frequency by summing
all frequencies for each prey species within each category for every study. We then
divided these values by the sum of all mammal frequencies combined for each
study, and calculated an average of these modied frequencies across all studies,
weighted by the study sample size (i.e., number of pellets analyzed).
Results
Pellet analysis
We collected and analyzed 176 vulture pellets. Of these, 130 were from summer
and 46 were from winter/spring. Sample composition by island was 47 from Lady’s
Island, 43 from Port Royal Island, and 86 from St. Helena Island. We documented
12 mammal species overall, with White-tailed Deer being the most common spe-
cies, present in 65% of samples, and constituting 35.73 average percent volume
(Table 2). The next most common mammals were Striped Skunks (present in 48%
of samples; 17.68 average percent volume) and Raccoons (22% of samples; 11.20
average percent volume). These 3 species collectively comprised 64% of prey in all
samples combined, with respective percent of overall volume consisting of 32.75,
20.18, and 11.15 for White-tailed Deer, Striped Skunks, and Raccoons, respectively.
Plant matter such as leaves, seeds, and bark was present in 85% of samples. Trash,
including plastic, glass, foil, and paper, was detected in 47% of samples; 30% of
samples contained plastic.
For White-tailed Deer, there was no inuence of season or island on frequency
or percent volume in pellets (Tables 3, 4). For Striped Skunks, we observed a 5%
increase in percent volume (β = 0.239, 85% CI= 0.007–0.925) and a 17% increase
in frequency (β = 0.756, 85% CI= 0.230–1.283) in winter/spring compared to sum-
mer, but no differences among islands. There was a 28% increase in frequency (β =
1.396, adjusted P-value=0.016) and 9% increase in percent volume (β = 0.811, ad-
justed P-value = 0.049, Table 5) of Raccoons in pellets on Lady’s Island compared
to Port Royal Island, but other pairwise comparisons were not signicant and there
was no inuence of season.
Literature review analysis
Our review contained 14 studies: 9 of Turkey Vultures, 1 of Black Vultures, and
4 of both species combined. There were 7 studies from the United States, 3 from
Mexico, and 1 each from Argentina, Chile, Canada, and the Falkland Islands. Re-
mains of 28 mammalian species were identied overall. Additionally, there were 6
items identied to the level of genus, and 5 to family. Weighted averages of modi-
ed frequencies were 56%, 36%, and 8% for large, medium, and small mammals,
respectively. The most common mammalian items were Bos Taurus L. (Cattle),
Ovis aries L. (Sheep), Sus domesticus Erxleben (Pig), Raccoons, Sylvilagus ori-
danus (J.A. Allen) (Eastern Cottontail), and Striped Skunks, each present in half of
studies. The next most common items were White-tailed Deer, Canis familiaris L.
(Domestic Dog), and Felis catus L. (Domestic Cat), each present in 6 studies. Five

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Table 2. Contents of Turkey Vulture and Black Vulture pellets (n = 176) collected from roosts in
coastal South Carolina, 2020. Frequency represents the number of pellets containing the item. Aver-
age volume is the modied average percent volume of the item in each pellet. Overall volume is the
percent of the item in all samples combined. “-“ indicates items that were excluded from modied
percent volume calculations.
Volume (%) (mean ± SD)
Frequency Average Overall
Plants 150 - -
Poaceae 93 - -
Quercus leaves 70 - -
Seeds 57 - -
Conifer needles 46 - -
Twigs 34 - -
Acorns/nuts 32 - -
Roots 20 - -
Wood/bark 14 - -
Bud scales 5 - -
Unidentied plants 3 - -
Arthropods 59 - -
Diptera 36 - -
Coleoptera 14 - -
Formicidae 12 - -
Arachnida 11 - -
Unidentied insects 13 - -
Reptiles 6 2.57 ± 14.82 4.14
Birds 135 - -
Mammals 165 - -
Odocoileus virginianus (White-tailed Deer) 115 35.73 ± 35.67 32.75
Mephitis mephitis (Striped Skunk) 85 17.68 ± 25.39 20.18
Procyon lotor (Raccoon) 56 11.20 ± 21.70 11.15
Unidentied animal 50 11.79 ± 25.54 13.44
Didelphis virginiana (Kerr) (Virginia Opossum) 40 6.88 ± 16.19 7.51
Sylvilagus oridanus (Eastern Cottontail) 10 2.33 ± 13.45 4.10
Ondatra zibethicus (L.) (Muskrat) 9 0.96 ± 4.56 0.84
Lontra canadensis (Schreber) (North American River Otter) 8 1.01 ± 5.60 0.53
Castor canadensis (Kuhl) (North American Beaver) 6 1.54 ± 10.93 2.70
Vulpes vulpes (L.) (Red Fox) 5 1.74 ± 12.40 2.41
Microtus pennsylvanicus (Ord) (Eastern Meadow Vole) 1 0.08 ± 1.07 0.12
Scalopus aquaticus (L.) (Eastern Mole) 1 0.28 ± 3.75 0.12
Sciurus carolinensis (Gmelin) (Eastern Gray Squirrel) 1 0.05 ± 0.75 0.01
Natural elements 9 - -
Soil 1 - -
Rock 8 - -
Anthropogenic 83 - -
Plastic 53 - -
Paper 21 - -
Polystyrene 7 - -
Glass 3 - -
Foil 5 - -
Painted wood 1 - -
String 1 - -
Other 10 - -

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species of birds were identied in addition to 3 families and 3 orders. Vegetation
was documented in pellets from 9 studies and anthropogenic debris in 5 studies.
Discussion
Black and Turkey Vultures in coastal South Carolina foraged primarily on
White-tailed Deer, but also consumed a diversity of other mammalian species. In
Table 4. Model averaged parameter estimates, standard error, and 85% condence intervals for aver-
age percent volume and frequency of major prey items in pellets collected from Turkey Vulture and
Black Vulture roosts in South Carolina, 2020.
Standard Lower Upper
Model Species Parameter Estimate Error CI CI
Average % volume
White-tailed Deer Season: Winter/Spring 0.03 0.22 -0.29 0.35
Striped Skunk Season: Winter/Spring 0.24 0.33 0.01 0.92
Raccoon Island: Port Royal -0.82 0.34 -1.31 -0.32
Island: St. Helena -0.16 0.30 -0.59 0.26
Season: Winter/Spring 0.39 0.34 -0.11 0.89
Frequency
Striped Skunk Season: Winter/Spring 0.76 0.36 0.23 1.28
Raccoon Island: Port Royal -1.41 0.51 -2.14 -0.67
Island: St. Helena -0.49 0.38 -1.04 0.05
Season: Winter/Spring 0.24 0.36 -0.03 1.06
Table 3. Model combinations for analysis of common mammal species in pellets collected from Tur-
key Vulture and Black Vulture roosts in South Carolina, 2020. Average percent volume is the mean
volume of the item in pellets and was examined with a linear model. Frequency is presence/absence
of the item in pellets and was analyzed using a generalized linear model with binomial distribution.
Output includes number of model parameters (K), sample size corrected Akaike’s information cri-
terion (AICc), Akaike weights (wi), log likelihood (LL), and difference in AICc between each model
and top model (ΔAICc). Cells with (+) indicate that the parameter was included in the model. Models
presented are those with ΔAICc < 2.
Model Species Island Season K LL AICc ΔAICc wi
Average % volume
White-tailed Deer 2 -404.96 814.00 0.00 0.64
+ 3 -404.92 816.00 1.99 0.24
Striped Skunk + 3 -356.88 719.90 0.00 0.40
2 -357.96 720.00 0.10 0.38
Raccoon + + 5 -330.60 671.60 0.00 0.54
+ 4 -332.55 673.30 1.78 0.22
Frequency
White-tailed Deer 1 -113.58 229.20 0.00 0.62
Striped Skunk + 2 -119.91 243.90 0.00 0.41
+ + 4 -117.95 244.10 0.25 0.36
1 -121.89 245.80 1.91 0.16
Raccoon + 3 -105.89 217.90 0.00 0.48
+ + 4 -104.98 218.20 0.27 0.42

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addition, they frequently ingested non-prey or indigestible items such as plant mat-
ter and trash. Deer constituted the most common prey item across all roost locations
and during both seasons examined. The substantial contribution of deer to vulture
diets supports the hypothesis that these species have benetted from greater car-
rion availability resulting from increasing deer populations and increasing rates of
wildlife–vehicle collisions (Hill et al. 2020). This conclusion is bolstered by our re-
view in which White-tailed Deer were present in 6 of the 7 studies from the United
States. A portion of these carcasses in our study were likely scavenged as roadkill,
since vehicle collisions are a common source of deer mortality on South Carolina
sea islands (Cromwell et al. 1999, Roberts 2007), and deer were frequently seen
as roadkill throughout the study area (A.E. Holland, pers. observ.). In the United
States, vehicle collisions account for nearly 10% of cause-specic mortality of
deer (Hill et al. 2019). Thus, a dense population of ungulates combined with high
amounts of vehicle mortality likely provides a reliable source of carrion that sup-
ports vulture populations in this area and across the United States.
Vehicle collisions may also contribute to the high consumption of Striped
Skunks and Raccoons, the second and third most common prey items, as they are
regularly killed by vehicle collisions (Barthelmess 2014, Hill et al. 2019). These
species were also among the most commonly documented in our literature review.
Increased consumption of skunks during the winter/spring season may reect high-
er rates of roadkill due to increased movement during the breeding season (Bixler
and Gittleman 2000, Feldhamer et al. 2003). Raccoons also breed in the winter/
spring season (Byrne and Chamberlain 2011), and both frequency and percent
volume of this species in pellets was higher during this period than in summer, but
not signicantly so. Conversely, frequency and percent volume of deer in pellets
was similar between the seasons examined. This result likely occurred because we
did not include fall, when breeding season occurs for deer in the region and when
roadkill rates are generally greater (Stickles et al. 2015). Consequently, deer may
constitute an even more important source of carrion than what we report when all
seasons are considered.
The extensive home ranges of both vulture species likely accounts for the
similar consumption of skunks and deer across islands. The annual mean home
ranges of these birds in South Carolina vary from 30.3 to 340.5 km2 (DeVault
Table 5. Pairwise comparisons between three South Carolina islands in 2020 for average percent vol-
ume and frequency of Raccoon remains in pellets of Turkey Vultures and Black Vultures.
Model Contrast Estimate Standard error P value
Average % volume
Lady's Island: Port Royal 0.811 0.343 0.0498
Lady's Island: St. Helena 0.231 0.292 0.7105
Port Royal: St. Helena -0.581 0.303 0.1378
Frequency
Lady's Island: Port Royal 1.396 0.507 0.0164
Lady's Island: St. Helena 0.532 0.372 0.3266
Port Royal: St. Helena -0.864 0.473 0.1613

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J.E. Hill, A.E. Holland, L.K. Brohl, B.M. Kluever, M.B. Pfeiffer, T.L. DeVault, and J.L. Belant
2022 Vol. 21, No. 1
et al. 2004, Holland et al. 2017). With the maximum distance between roosts of
~25 km, it is likely that vultures roosting on different islands had overlapping
foraging areas, leading to similarities in prey consumption. Thus, the decreased
consumption of Raccoons on Port Royal Island compared to Lady’s Island was
somewhat unexpected. Possible explanations for this result may include a re-
duced abundance of Raccoons or availability of more preferred types of carrion
on Port Royal Island (DeVault et al. 2017). A notable caveat is that there was no
distinction in Raccoon consumption between Port Royal Island and St. Helena
Island, suggesting there was not an overall pronounced decline in Raccoon con-
sumption on Port Royal among all islands. Nevertheless, these results suggest
the potential for differences in consumption of some prey species by vultures
across a relatively small area. A study based on stable isotopes in feathers docu-
mented similarly divergent Turkey Vulture diets across an equally narrow spatial
distribution (Blázquez et al. 2016).
Our results indicate extensive consumption of garbage by vultures in this study
area. Trash and other anthropogenic items were present in almost half of pellets, a
frequency higher than many of the studies in our review. Several pellets contained
plastic bags, which vultures commonly ingest while eating garbage, and some pel-
lets contained seeds from produce such as oranges, melons, and cucumbers, that
were likely also consumed when eating trash (Torres-Mura et al. 2015). Prevalence
of garbage consumption at our study probably reects the amount of anthropogenic
development and substantial human presence, as trash ingestion by vultures is posi-
tively associated with urbanization (Ballejo et al. 2021). Efforts to manage vulture
populations in this area, and other sites with high human densities, should thus in-
clude waste management practices that reduce garbage availability to vultures (de
Araujo et al. 2018). In addition to management implications, garbage consumption
can have adverse impacts on the health of vultures, including nestlings when trash
is transferred to them by adults when provisioning their young (Pfeiffer et al. 2017,
Plaza and Lambertucci 2018). Although it is unlikely that trash consumption poses
a substantial risk to vultures in this area, garbage consumption may be a signicant
mortality risk for vulture populations that are of conservation concern (Houston et
al. 2007).
Vultures may also intentionally consume non-prey items, accounting in part for
the high amounts of trash and plant matter we recorded in pellets. One explanation
for this behavior is that vultures are naturally curious animals that display explorato-
ry foraging to locate novel food items (Houston et al. 2007). We frequently observed
Black Vultures tearing at and pulling up tarps that we placed on the ground for pellet
collection. On one instance, we observed 3 Black Vultures picking up pellets from
the tarp, shaking them, and consuming items that fell out. Vultures also tear at other
anthropogenic items such as car upholstery and roof shingles, which contributes to
conict with humans (Lowney 1999). Although the reasons for ingesting anthropo-
genic items are not entirely understood, the exploratory foraging behavior of vultures
may contribute to ingestion of these items, particularly in locations such as ours
where human presence has a pronounced inuence on the landscape.

Southeastern Naturalist
J.E. Hill, A.E. Holland, L.K. Brohl, B.M. Kluever, M.B. Pfeiffer, T.L. DeVault, and J.L. Belant
2022 Vol. 21, No. 1
22
Ingestion of seeds, present in one third of the pellets, could have occurred through
multiple mechanisms. As mentioned, seeds from produce may have been consumed
while eating trash (Torres-Mura et al. 2015). Seeds from other sources such as grasses
could have been consumed incidentally while scavenging carcasses, which may also
be partially the source of other plant matter (Elías 1987, Kelly et al. 2007). Interest-
ingly, some pellets with seeds contained sections of digestive tracts, indicating that
seed ingestion could occur secondarily as the result of scavenging. Studies examin-
ing the ecosystem services of vultures have focused on carcass removal or nutrient
dispersal (e.g. DeVault et al. 2016), but the potential for vultures to disperse seeds
has received relatively little attention (but see Perez-Mendez and Rodriguez 2018).
The high frequency of seed ingestion indicates that vultures may play a role in seed
dispersal and subsequent plant community structure, which should be considered in
future efforts to quantify the ecosystem services of avian scavengers.
Despite the wide geographic range of studies in our review, there were some
commonalities. Pigs, Sheep, and Cattle were present in half of studies, including
those from different continents, suggesting that these vulture species have beneted
from modern livestock practices. Overall, vultures consumed primarily large mam-
mals and foraged on medium mammals to a lesser extent, whereas small mammals
such as rodents comprised less than 10 percent of prey consumption. These trends
suggest that large mammals often constitute most carrion consumed by these vul-
ture species, which may result from their foraging behavior. Larger carcasses likely
produce stronger olfactory cues during decomposition, which Turkey Vultures rely
on to locate carrion (Byrne et al. 2019, Grigg et al. 2017). Black Vultures primar-
ily use visual cues, and large carcasses are also more visually conspicuous (Grigg
et al. 2017). Furthermore, larger carcasses attract greater aggregations of vultures,
which serve as an additional cue for carcass presence (Houston 1988). Congruently,
Turkey Vultures and Black Vultures at another area in South Carolina scavenged
extensively on Pig carcasses, less frequently on rabbit carcasses, and mostly did
not scavenge rat carcasses (Turner et al. 2017). In the case of livestock, farms or
carcass-disposal sites may provide carrion reliably, leading vultures to scavenge
these carcasses more regularly compared to those of wild animals, the existence of
which are unpredictable in time and space (Kelly et al. 2007, López-López et al.
2014, Ruxton and Houston 2004).
Our study is subject to some constraints that may impact conclusions. Passage
through the vulture digestive tract degraded some hairs to the point that they could
not be identied to species, with 13% of the overall percent volume consisting of
unidentied hairs. As such, there may be some prey species we did not identify. As
all roosts were mixed species, we were unable to determine the vulture species that
produced each pellet, precluding an interspecic analysis of diet; interspecic dif-
ferences in diet could be substantial given contrasting foraging strategies between
species (Holland et al. 2019). Logistical limitations resulted in a much smaller
sample size for winter/spring compared to summer, which somewhat tempers our
conclusions regarding seasonal patterns in diet. Lastly, our literature review is
based on a relatively small sample of studies given the current geographic range of

Southeastern Naturalist
23
J.E. Hill, A.E. Holland, L.K. Brohl, B.M. Kluever, M.B. Pfeiffer, T.L. DeVault, and J.L. Belant
2022 Vol. 21, No. 1
these vultures. As a result, different patterns in diet may be identied from studies
representing a more comprehensive span of the species’ distributions.
The variety of prey items and trash ingestion identied in our review and pellet
analysis emphasizes the dietary versatility of Black Vultures and Turkey Vultures,
which probably accounts in part for their recent range expansions and population
increases. Several adaptations likely give them a unique ability to exploit anthro-
pogenic food. Due to their specialized digestive system, vultures can process items
like bones and decaying esh unpalatable to other animals, which results in a
relatively broad dietary niche breadth (Blázquez et al. 2016, Mendoza et al. 2018).
Relatedly, scavenging behavior played a primary role in the expansion of Threski-
ornis aethiopicus (Latham) (Sacred Ibis) in Africa (Clergeau and Yésou 2006).
Turkey Vultures also demonstrate highly dexterous foraging, such as scavenging
porcupines without consuming quills or peeling toads’ skin to avoid toxins in the
epidermis, which may permit them to consume items physically inaccessible to
other birds (Platt and Rainwater 2009, Platt et al. 2016). Lastly, vultures can learn
to use novel foods provided by humans due to their cognitive abilities (Sazima
2007). Widespread anthropogenic food occurrence coupled with a unique ability
to capitalize on this resource has likely contributed to the recent proliferation of
Turkey Vultures and Black Vultures across the Western Hemisphere.
Our pellet analyses and literature review indicate that humans may provision
food directly to vultures through trash, livestock, and roadkill, but also indirectly
by contributing to the growth of ungulate populations. As food availability heavily
inuences vulture presence, strategies such as garbage management and roadkill
removal may help reduce local vulture abundances and resultant conict with hu-
mans (e.g., de Araujo et al. 2018). Additionally, consumption of trash and seeds
combined with large home ranges could result in vultures dispersing garbage or
invasive species seeds across the landscape (Augé 2017, Ballejo et al. 2021, Perez-
Mendez and Rodriguez 2018). Thus, effective management may not only reduce
human–vulture conict but also alleviate some of the less visible but potentially
deleterious environmental impacts of high-density vulture populations.
Acknowledgments
J. Humphrey assisted with initial eld reconnaissance. Stone Laboratory of The Ohio
State University provided use of microscopes. This research was supported in part by the
US Department of Agriculture, Animal and Plant Health Inspection Service, Wildlife Ser-
vices, and the US Air Force. The ndings and conclusions in this article are those of the
authors and do not necessarily represent the views of the US Fish and Wildlife Service or
the US Department of Agriculture.
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