English

An_Advanced_Method_to_Assess_t.PDF

An Advanced Method to Assess the Diet of Free-Ranging Large Carnivores Based on Scats Bettina Wachter1*, Anne-Sophie Blanc2, Jörg Melzheimer1, Oliver P. Höner1, Mark Jago3, Heribert Hofer1

1 Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany, 2 Institute of Zoology, University of Neuchâtel, Neuchâtel, Switzerland, 3 The

AfriCat Foundation, Otjiwarongo, Namibia

Abstract

Background: The diet of free-ranging carnivores is an important part of their ecology. It is often determined from prey remains in scats. In many cases, scat analyses are the most efficient method but they require correction for potential biases. When the diet is expressed as proportions of consumed mass of each prey species, the consumed prey mass to excrete one scat needs to be determined and corrected for prey body mass because the proportion of digestible to indigestible matter increases with prey body mass. Prey body mass can be corrected for by conducting feeding experiments using prey of various body masses and fitting a regression between consumed prey mass to excrete one scat and prey body mass (correction factor 1). When the diet is expressed as proportions of consumed individuals of each prey species and includes prey animals not completely consumed, the actual mass of each prey consumed by the carnivore needs to be controlled for (correction factor 2). No previous study controlled for this second bias.

Methodology/Principal Findings: Here we use an extended series of feeding experiments on a large carnivore, the cheetah (Acinonyx jubatus), to establish both correction factors. In contrast to previous studies which fitted a linear regression for correction factor 1, we fitted a biologically more meaningful exponential regression model where the consumed prey mass to excrete one scat reaches an asymptote at large prey sizes. Using our protocol, we also derive correction factor 1 and 2 for other carnivore species and apply them to published studies. We show that the new method increases the number and proportion of consumed individuals in the diet for large prey animals compared to the conventional method.

Conclusion/Significance: Our results have important implications for the interpretation of scat-based studies in feeding ecology and the resolution of human-wildlife conflicts for the conservation of large carnivores.

Citation: Wachter B, Blanc A-S, Melzheimer J, Höner OP, Jago M, et al. (2012) An Advanced Method to Assess the Diet of Free-Ranging Large Carnivores Based on Scats. PLoS ONE 7(6): e38066. doi:10.1371/journal.pone.0038066

Editor: Brock Fenton, University of Western Ontario, Canada

Received September 17, 2011; Accepted April 30, 2012; Published June 8, 2012

Copyright: � 2012 Wachter et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This study was financed by the Messerli Stiftung, the Université Neuchâtel, the Fond Wüthrich et Mathey-Dupraz (all Switzerland) and the Leibniz Institute for Zoo and Wildlife Research, Germany. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.

* E-mail: [email protected]

Introduction

Diet is an important part of carnivore ecology and conservation.

Information on diet composition is needed when predator-prey

relationships are studied [1], when predators are perceived as

a threat to livestock of farmers [2] or when rare prey species may

need to be protected [3]. Due to the elusive behaviour of many

carnivore species and the small chances of finding fresh kills, indirect

methods of determination of carnivore diets based on indigestible

prey remains in scats such as hairs, bones, teeth, hooves and claws is

often the most appropriate, accurate and feasible method. This

method allows the determination of the range of prey species

consumed by carnivores, the frequency at which remains of prey

species occur in scats and the proportion each prey species

contributes to the diet. The latter, which is often the information

needed, cannot be calculated directly from the frequency at which

remains of prey species occur in scats because smaller animals have

a higher surface-to-volume (hair-to-meat) ratio than larger animals

[4]. This affects the production of scats: When carnivores feed from

a small prey animal, they consume less prey mass to excrete one scat

than when they feed from a large prey animal [2,5,6]. This is

consistent with the finding that smaller animals are less digestible

than larger animals [7]. As a result, the frequency of occurrence of

prey species in scats is likely to over-represent smaller prey animals in

terms of consumed prey mass in the diet [4].

The conversion of prey body mass into a number of scats and

their weights excreted by an individual carnivore after prey

consumption is a crucial step that diet studies based on scats ought

to infer accurately. We use seven quantities to evaluate the steps

required to establish the consumed prey mass and the number of

consumed prey individuals derived from carnivore scats collected

in the field (Fig. 1). By applying these quantities to different

sampling schemes (scat collection schedules) and carnivore group

sizes we demonstrate that previous procedures were not aware of

an important source of bias and introduce a new correction factor

to take this bias into account.

Diet Expressed as Proportions of Consumed Prey Mass To control for the influence of prey body mass (Q1) on the

consumed prey mass to excrete one scat (Q5), previous studies

PLoS ONE | www.plosone.org 1 June 2012 | Volume 7 | Issue 6 | e38066

established a correction factor ( = correction factor 1, CF1) using

feeding experiments (wolves (Canis lupus): [5,7–9], cougar (Felis

concolor): [6], cheetah (Acinonyx jubatus): [2]). These studies applied

the widely used ‘biomass model’ [5] which is based on a linear

regression (y=ax + b) with x being the provided prey body mass

(Q1) and y being the consumed prey mass to excrete one scat

(Q5). The diet in terms of the proportions of consumed mass per

species is then determined by multiplying the frequency of

occurrence of prey species i identified in n collected scats (ni) by y

for prey species i ( =Q5i) using the (reasonable) assumption of

prey body mass x=Q1i [2,5,10–13]. Thus, the consumed mass of

prey species i by a carnivore can be described as ni6Q5i. Other

studies determined CF1 for a given prey species by calculating

the ratio of consumed mass to dry mass of prey remains in scats

and determined the diet in terms of the proportion of consumed

mass per species using this CF1 (wolves: [14,15], lynxes (Lynx

lynx): [15,16]).

Possibly because of providing a limited range of prey body

masses, all previous studies that conducted feeding experiments to

determine CF1 fitted a linear regression to their data [2,5–9,16]. A

linear regression suggests that consumed prey mass to excrete one

scat does not reach an asymptote for large prey body mass. We

would expect that consumed prey mass to excrete one scat reaches

such an asymptote because there will be a limit to the prey mass

consumed by a carnivore which can be digested per excreted scat

and there will be a limit to the size of scats that can be excreted.

The regressions therefore should approach an asymptote, hence

follow a non-linear function, which we assess to be physiologically

more meaningful and realistic.

We evaluated this possibility in the cheetah, a species for

which a previous study used a linear relationship between y and x

[2]. We conducted a series of feeding experiments that included

the entire range of body sizes of potential prey [17] as well as

prey animals of sizes larger than a single cheetah is able to kill.

Inclusion of prey of sizes that a carnivore may not be able to

overcome alone but only in a group, or not even then, provides

information on the overall physiological characteristics of the

digestive system. Even if the predator in the wild only feeds from

a fraction of the presented range of prey sizes of the feeding

trials, the knowledge of the digestive properties for prey weights

ranging across several orders of magnitude improves the

accuracy of CF1 for any individual prey size. This is because

the prey mass consumed per excreted scat for a particular prey

size is a function of the overall physiological characteristics. Also

for predator species mainly feeding on prey species smaller than

its own body mass, it is advisable to use prey masses across a large

range for the feeding experiment to allow a more accurate

estimation of CF1 also for the small prey species. For carnivore

species mainly feeding on fruits, invertebrates, birds and small

mammals such as black-backed jackals (Canis mesomelas), side-

striped jackals (Canis adustus) and red fox (Vulpes vulpes), we suggest

that the specific conversion factors from feeding experiments with

these food items should be used [18,19,20,21] and diet de-

termined following the extensive outline and review of [21].

Diet Expressexd as Proportions of Consumed Individuals Studies may not only be interested in the biomass of prey

consumed by a carnivore but also, or primarily, in the number of

Figure 1. The seven quantities derived from carnivore scats. These quantities describe the conversion of prey body mass into numbers and weights of collectable scats excreted by a carnivore individual after prey consumption and the determination of prey digestibility. doi:10.1371/journal.pone.0038066.g001

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 2 June 2012 | Volume 7 | Issue 6 | e38066

prey individuals consumed [2,5,13,15]. The number of consumed

individuals of a given prey species i is commonly established by

dividing the consumed mass of prey species i, which is ni6Q5i, by

the entire body mass of the consumed prey species i, i.e. (ni6Q5i)/

Q1i. Such calculations, however, are only appropriate when the

carnivore consumes the prey animal entirely, but not when it

consumes only part of it, as this leads to an underestimate of the

numbers of large prey animals consumed. To our knowledge this

issue has not been considered in previous studies [2,5,13,15],

although most large carnivores do not completely consume large

prey [1,2,5,22]. To account for this bias, the number of prey

individuals in the diet should be calculated on the basis of the

actual prey mass consumed (Q3) as suggested by [17]. The number

of consumed individuals of prey species i is then equivalent to

(ni6Q5i)/Q3i for solitary carnivores and ((ni6Q5i)/Q3i)/Q2 for

carnivores feeding in groups with a mean size of Q2. Because

Q5i=Q3i/Q4i, Q5i can be substituted by Q3i/Q4i. The number of

consumed individuals per prey species i is then simply ni/Q4i for

solitary carnivores and (ni/Q4i)/Q2 for carnivores feeding in groups

with a mean size of Q2. Q4i is the number of scats excreted after

consuming prey species i and can be derived from the feeding

experiments using a regression between the number of excreted

scats (Q4) and body mass (Q1). We termed this regression

correction factor 2 (CF2).

These calculations are suggested if the prey species is large, the

consumption of one individual (one feeding event) is likely to

produce more than one scat and scats are collected in a defined

area at regular intervals (daily, weekly or monthly) so that all

detected scats excreted in the last couple of days or weeks are

collected. Under the assumption that the likelihood of finding scats

with remains of one feeding event of a given prey species is similar

to the likelihood of finding scats with remains of different feeding

events of the same prey species, scats containing remains of this

prey species from one sampling interval can be pooled. Then,

these scats should be treated as dependent samples and several

scats assumed to represent one feeding event.

In contrast, if single carnivores of known identity are followed

and observed to defecate or are immobilised and directly sampled,

and if the sampling interval is longer than the time period during

which a carnivore excretes scats after having fed on one prey

animal, the scats are independent samples and cannot originate

from one feeding event. In this case each scat containing remains

of a particular prey species has to be multiplied by the mean

number of scats a carnivore excreted after consuming from such

a prey animal (Q4) to account for the missed scats of the carnivore

individual. The number of consumed individuals per prey species

is then equivalent to ((ni6Q4i)6Q5i)/Q3i for solitary carnivores and

for carnivores feeding in groups since only one group member was

sampled. Because Q5i=Q3i/Q4i, Q5i can be substituted by Q3i/Q4i

and the number of consumed individuals per prey species for scats

collected independently from each other is simply ni. It is

important to be aware of whether scats collected in the field arise

from one feeding event (dependent objects) or from independent

feeding events, because the results and therefore the interpretation

differ substantially.

In this study we introduce for the first time a CF1 based on

a non-linear function and the new CF2 using a calibration study

with cheetahs. We illustrate the application of both correction

factors and contrast it with results obtained from the conventional

method with a hypothetical example, and then proceed with

calculations on the basis of both scat sampling schemes and for

three different feeding group sizes. Using our protocol, we also

derive CF1 and CF2 for other carnivore species from published

data and apply them to published studies. We discuss the diet

composition derived with the new method in comparison with

results obtained from the conventional method.

Methods

Study Site We conducted feeding experiments in north-central Namibia at

AfriCat Foundation (20u519S, 16u409E). AfriCat Foundation is

registered by the Namibian Ministry of Environment and Tourism

(MET) as a large non-profit carnivore captive facility since 1993

(permit office 2004/11) and runs a rehabilitation centre for free-

ranging carnivores, mainly cheetahs. AfriCat is equipped with

high standard veterinary facilities and qualified staff caring for the

animals.

Ethics Cheetahs are capable of killing a wide range of prey species.

Reports range from hares (Lepus sp.) that weigh about 2 kg to adult

zebra (Equus burchelli) that weigh up to 270 kg [23]. Cheetahs hunt

either solitarily or in groups consisting of mother and cubs or male

coalitions, with larger groups hunting larger prey animals [22].

Scat analyses of cheetahs further revealed that cheetahs also feed

on prey species that are smaller than hares such as mice [17].

For the feeding experiments we used kudu (Tragelaphus

strepsiceros), gemsbok (Oryx gazella), hartebeest (Alcelaphus buselaphus),

springbok (Antidorcas marsupialis), warthog (Phacochoerus africanus),

goat (Capris sp.), springhare (Pedetes capensis), ground squirrel (Xerus

inauris), Namaqua rock mouse (Aethomys namaquensis) and hairy-

footed gerbil (Gerbillurus paeba) as prey species. All large carcasses

were animals killed by trophy hunters who booked their hunting

with a registered professional Namibian hunting guide who had

a hunting permit from the Ministry of Environment and Tourism

(MET) in Windhoek, Namibia. Once the animal was shot in the

field according to the hunting regulations from the NAPHA

(Namibian Professional Hunting Association) and the trophy, i.e.

head and horns, was removed, we retrieved the carcass. The

smaller animals were trapped at the farms where our research

stations are based. Commercial mouse traps of different sizes were

used and once an animal was trapped it was quickly killed. Our

study was approved by the MET (permit number 1089/2006), the

scientific advisory board of the AfriCat Foundation and the

leadership and Ethical Committee of the Leibniz Institute for Zoo

and Wildlife Research in Berlin.

Feeding Experiments Between August 2006 and December 2006 we conducted fifteen

feeding experiments on twelve cheetahs in four groups (two groups

of four, one group of three and one single). During the

experiments, the cheetahs were kept in observation enclosures of

20 m610 m provided with water ad libitum. We provided cheetahs

with prey animals weighing between 0.04 kg and 214 kg; we

measured the mass of prey animals provided to and consumed by

cheetahs in kg to an accuracy of 0.2 g using an electronic scale for

prey animals up to 3.5 kg, and to an accuracy of 0.1 kg using

a spring scale for larger prey animals. Large prey animals were fed

to large groups to simulate natural feeding situations. For prey

species smaller than springhare, more than one carcass was

provided to avoid depriving the cheetahs of food (Table 1). In

these cases, the cheetahs were given a carcass only after they

stopped feeding on the previous carcass. We conducted three or

four feeding experiments per cheetah group (Table 1), with

intervals of between 8 and 21 days (mean 6 sd: 14.364.1 days)

between experiments.

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 3 June 2012 | Volume 7 | Issue 6 | e38066

T a b le

1 . P re y sp e ci e s an

d p re y b o d y m as s p ro vi d e d to

ch e e ta h s d u ri n g 1 5 fe e d in g e xp

e ri m e n ts ,p

re y m as s co n su m e d an

d sc at s e xc re te d b y ch e e ta h s, p re y m as s co n su m e d p e r

co lle ct ab

le sc at

an d d ig e st ib ili ty

o f p re y sp e ci e s.

P re y

P re y p ro

v id e d

C h e e ta h g ro

u p

P re y co

n su

m e d

S ca

ts e x cr e te d

C o n su

m e d p e r

co ll e ct a b le

sc a t

D ig e st ib il it y

S p e ci e s

n M e a n k g

( Q 1 )

S iz e

(Q 2 )

ID K g

M e a n k g p e r ch

e e ta h

a n d p re y (Q

3 )

n co

ll e c-

ta b le

n n o n -

co ll e ct a b le

n co

ll e ct a b le

p e r

ch e e ta h a n d p re y ( Q

4 )

M e a n k g o f co

ll e ct a b le

p e r ch

e e ta h a n d p re y (Q

6 )

K g

(Q 5 = Q 3 /Q

4 )

% (Q

7 = (Q

3 2

Q 6 )*

1 0 0 /Q

3 )

K u d u

1 2 1 4 .0 0

4 A

2 8 .0 0

7 .0 0

1 0

2 2 .5 0

0 .1 6 2 c

2 .8 0

9 7 .6 9

G e m sb o k

1 1 1 8 .2 5

4 B

2 3 .2 5

5 .8 1

1 1

– 2 .7 5

0 .2 2 6

2 .1 1

9 6 .1 2

G e m sb o k

1 1 0 6 .5 0

4 A

2 5 .0 0

6 .2 5

9 –

2 .2 5

0 .1 4 1

2 .7 8

9 7 .7 5

K u d u

1 1 0 6 .0 0

4 B

1 6 .5 0

4 .1 3

1 0

– 2 .5 0

0 .1 9 3

1 .6 5

9 5 .3 3

H ar te b e e st

1 9 8 .7 5

4 B

2 1 .7 5

5 .4 4

1 0

– 2 .5 0

0 .1 6 6

2 .1 8

9 6 .9 6

W ar th o g

1 6 8 .5 0

3 C

1 7 .5 0

5 .8 3

3 1

1 .0 0

0 .1 2 1

5 .8 3

9 7 .9 3

W ar th o g

1 6 8 .0 0

4 A

2 4 .0 0

6 .0 0

8 4

2 .0 0

0 .1 3 7 d

3 .0 0

9 7 .7 1

Sp ri n g b o k

1 2 9 .2 5

4 B

2 1 .7 5

5 .4 4

1 1

– 2 .7 5

0 .3 2 4

1 .9 8

9 4 .0 4

G o at

1 2 4 .0 0

4 A

1 3 .0 0

3 .2 5

8 1

2 .0 0

0 .1 8 8

1 .6 3

9 4 .2 3

Sp ri n g b o k

1 2 3 .0 0

3 C

1 7 .0 0

5 .6 7

1 0

– 3 .3 3

0 .3 2 8

1 .7 0

9 4 .2 2

Sp ri n g h ar e

1 3 .5 0

1 D

2 .9 8

4 –

4 .0 0

0 .2 4 2

0 .7 5

9 1 .8 8

Sp ri n g h ar e

3 2 .8 3

3 C

8 .2 1

2 .7 4

8 –

2 .6 7

0 .3 4 0

1 .0 3

8 7 .5 8

Sq u ir re l

1 5

0 .5 3

3 C

6 .9 5

0 .4 6 b

9 2

0 .6 0

0 .0 6 1 e

0 .7 7

8 6 .9 0

Sq u ir re l

4 0 .5 0

1 D

1 .7 5

0 .4 4

3 –

0 .7 5

0 .0 4 3

0 .5 8

9 0 .2 9

M o u se /G e rb il

1 4

0 .1 0 6 a

1 D

1 .4 9

0 .1 0 6 a

6 1

0 .4 3

0 .0 2 2 f

0 .2 5

7 9 .0 6

C o rr e ct io n fa ct o rs 1 (C F1 ) an

d 2 (C F2 ) w e re

d e te rm

in e d b y fi tt in g (1 ) an

e xp

o n e n ti al re g re ss io n to

co n su m e d p re y m as s p e r co lle ct ab

le sc at

(Q 5 ) as

a fu n ct io n o f m e an

p re y b o d y m as s p ro vi d e d p e r fe e d in g e xp

e ri m e n t (Q

1 ) (=

C F1 )

an d (2 ) a p e ak

lo g ar it h m ic n o rm

al fu n ct io n to

th e n u m b e r o f e xc re te d co lle ct ab

le sc at s (Q

4 ) as

a fu n ct io n o f m e an

p re y b o d y m as s p ro vi d e d p e r fe e d in g e xp

e ri m e n t (Q

1 ) (=

C F2 ). Fo

r d e ta ils

se e te xt .a

1 4 m ic e an

d g e rb ils

w it h a to ta l

w e ig h t o f 1 .4 9 kg

w e re

e at e n e n ti re ly , th e re m ai n in g 6 6 w it h a to ta l w e ig h t o f 2 .7 4 kg

w e re

re je ct e d . C al cu la ti o n s w e re

b as e d o n th e co n su m e d m ic e an

d g e rb ils . b e ac h ch e e ta h fe d fr o m

fi ve

su b se q u e n tl y p ro vi d e d sq u ir re ls .c

– f

m e an

kg o f co lle ct ab

le sc at s p e r ch e e ta h ar e b as e d o n m e an

w e ig h ts

o f si x,

se ve n , se ve n an

d fo u r co lle ct ab

le sc at s, re sp e ct iv e ly , m u lt ip lie d b y th e n u m b e r o f co lle ct ab

le sc at s p e r ch e e ta h .

d o i:1 0 .1 3 7 1 /j o u rn al .p o n e .0 0 3 8 0 6 6 .t 0 0 1

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 4 June 2012 | Volume 7 | Issue 6 | e38066

Following [5], we divided the feeding experiments into three

periods: (1) the fasting period before feeding, (2) the feeding day

and (3) the fasting period after feeding. During period 1, we

removed all cheetah scats each day until no more scats were

excreted or until we identified only grass or cheetah hairs in the

excrements. Twenty-four hours later, we fed the cheetahs with

prey animal(s). Cheetahs fed on the carcasses for between

59 minutes (squirrels) and 3 hours 34 minutes (warthog) with

a mean 6 sd of 2 hours 40 minutes 652 minutes (n=13).

Approximately ten minutes after the last cheetah of the group

stopped feeding, we collected and weighed the remains of the

carcass(es). In two feeding experiments with a goat and a spring-

hare the cheetahs were still feeding after 3 hours 25 minutes and

2 hours 30 minutes, respectively, when darkness set in at 19:00 h.

In these cases the carcass was left over night and we collected and

weighed all remains the next morning. During period 3, we again

collected all scats during each day until the cheetahs excreted no

more scats or only scats containing grass or cheetah hairs. We

distinguished between ‘collectable’ (hard to soft) and ‘non-collect-

able’ (viscous) scats according to their consistency and included

only collectable scats in the determination of correction factors to

provide correction factors suitable for field studies [2,5,7–9]. We

counted all collectable and non-collectable scats, and weighed

collectable scats spatially separated from non-collectable scats to

an accuracy of 2 g. Non-collectable scats covered collectable scats

in a few cases, preventing their weighing.

Data Analysis We determined CF1 by calculating consumed prey mass per

excreted collectable scat (Q5) for each feeding experiment ( =Q3/

Q4) and fitting an exponential function of this parameter on mean

prey body mass provided per feeding experiment (Q1) which is

a representation of an asymptotic process (Table 1). When we

provided more than one carcass, we used the mean of the

consumed mass of each carcass. For mice and gerbils we only

included those animals that were eaten by the cheetah (n=14,

mean weight = 0.106 kg), not those that were rejected and left

untouched (n=66, mean weight = 0.042 kg). We determined CF2

by fitting a non-linear regression of the number of excreted

collectable scats per cheetah and prey animal (Q4) on mean prey

body mass provided per feeding experiment (Q1). We initially

expected this to also be an asymptotic process, best represented by

an exponential function. Alternatively, if at large prey sizes either

the behaviour of the predator or the ratio of digestible to

indigestible matter changes, then it is possible that the number of

excreted collectable scats might decline again. Such a process is

usefully represented by a peak logarithmic function. For our study

the peak logarithmic function runs best through the data; in the

supporting information we also present the exponential function

(Fig. S1). For data sets from the literature (see discussion) we use

the exponential function; for the Indian wolf (Canis lupus papllipes)

we also compare the fit of the exponential function with that of the

peak logarithmic function (Table S1).

The application of the correction factors to scats collected in the

field and the subsequent determination of the diet were based on

weights of prey animals consumed by cheetahs. Since identified

prey remains in scats rarely provide information on their age and

thus approximate weight of the consumed prey individual, age

categories of the prey species were estimated and corresponding

weights applied [2,5,13,15]. For the hypothetical example, we

chose for each prey species the age category most likely to be killed

by cheetahs. These were adults of goat, springbok, duiker

(Sylvicapra grimma), steenbok (Raphicerus campestris), springhare and

squirrel [24–26], juveniles of kudu and hartebeest [27], calves of

gemsbok [24,28] and piglets of warthog [28]. Since cheetahs might

also kill other age categories, we discuss how the results will be

affected when choosing different age categories and hence prey

sizes.

We determined the apparent digestibility for different prey sizes

as (mean fresh prey mass consumed per cheetah – mean fresh

collectable scat mass per cheetah)*100/mean fresh prey mass

consumed per cheetah [15,29], i.e. (Q3– Q6) * 100/Q3. This

digestibility is termed ‘apparent’ because the scats contain also

metabolic components from the animal and the fresh scat might

also include fluid originating from drinking by the cheetahs

[15,29]. When not all collectable scats could be weighed, we

calculated the mean fresh collectable scat mass per cheetah by

multiplying the mean weight of the weighed scats by the number

of collectable scats (Table 1). We performed all non-parametric

tests and regressions using SYSTAT 13.0 (Systat Software Inc.).

Results

One hundred and twenty (92%) of the 131 scats were collectable

scats (Table 1). The ratio of collectable to non-collectable scats

when cheetahs were fed with small prey species (springhare,

ground squirrel, mouse/gerbil) was similar to that when cheetahs

were fed with large prey species (kudu, gemsbok, hartebeest)

(Fisher’s exact test, P=0.37, n=85).

Correction Factor 1 The amount of food from one prey animal a cheetah consumed

to excrete one collectable scat (Q5) increased with prey body mass

(Q1) and levelled out at certain weight of prey body mass. This

relationship, the CF1, was described by the exponential function

y=2.358(1-exp(20.075x)) with 2.358 kg being the consumed prey

mass per collectable scat at which the curve reaches an asymptote

(R2=0.731, P,0.05, n=14) (Fig. 2). The warthog with 5.83 kg

eaten per collectable scat (Table 1) was excluded from this

regression because its residual (3.07) from the regression line was

3.3 standard deviations from the mean of the residuals of all 15

feeding trials (mean 6 sd: 0.6260.74) and thus regarded as an

outlier; its inclusion resulted in a similar equation with a lower fit

(y=2.821(1-exp(20.057x)), R2=0.493, P=ns, n=15).

Apparent digestibility (y=Q7) increased with increasing mean

prey body mass per feeding experiment (x=Q1) and levelled out at

94.2% (y=94.192(1-exp(217.222x)), R2=0.541, P,0.001, n=15).

Application of Correction Factor 1 The hypothetical example consisted of 100 scats. In these scats,

10 prey species were chosen, each of which was represented in 10

scats. The relative frequency of occurrence for each prey species

was 10% (Table 2, column n). When applying the empirically

determined CF1 to calculate the consumed prey mass per

collectable scat (Table 2, column Q5), the consumed prey mass

per species was lowest for small prey species (Table 2, column

n * Q5).

Correction Factor 2 The mean number of excreted collectable scats per cheetah and

prey animal (y=Q4) increased with mean prey body mass (x=Q1)

and then decreased again (Fig. 3). This relationship was described

by a peak logarithmic normal function with three parameters

(y=3.094exp(-0.5((ln(x/16.370))/2.584)2), R2=0.626, n=14,

Fig. 3) with a peak mean number of 3.1 excreted collectable scats

per cheetah and prey animal at 16.4 kg of mean prey body mass

provided (the first and third coefficient in the equation). Mean

mass (kg) of collectable scats per cheetah and prey animal (y=Q6)

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 5 June 2012 | Volume 7 | Issue 6 | e38066

similarly first increased with the provided mean prey body mass

(x=Q1) and then decreased again (y=0.310exp(20.5((ln(x/

11.600))/2.022)2), R2=0.696, n=14), with a peak mean collect-

able scat weight of 0.31 kg per cheetah and prey animal at

11.60 kg of mean prey body mass provided. The outlier of the

warthog with 1 excreted collectable scat per cheetah (Table 1) was

excluded from both analyses.

Sampling Regime and Application of Correction Factor 2 In the hypothetical example, application of CF2 for scats

collected by a regular sampling scheme (e.g. daily, weekly,

monthly) for solitary cheetahs revealed the highest number of

individuals consumed for small prey animals, the lowest number

for medium-sized prey animals and a medium number for large

prey (Table 2, column n/Q4). This contrasts with the results of the

conventional method (dividing consumed mean mass per prey

species by the entire prey weight Q1) where large prey species

showed the lowest number in the diet (Table 2, column n * Q5/Q1).

The numbers of the three prey species with the highest mass in the

example, juvenile kudu, juvenile hartebeest and adult goat, were

17.5 times, 10.8 times and 6.6 times higher when using CF2 than

the conventional method (Table 2). When scats were collected

independently, the number of consumed individuals is n (Table 3).

Discussion

Our study demonstrates that carefully correcting for biases

inherent in indirect methods of diet determination has a profound

effect on the assessment of diet composition and the estimated

number of prey animals killed by a carnivore population.

Correction Factor 1 Our results confirmed that the accuracy of CF1 depends on the

number of feeding experiments and the range of prey sizes

included. All previous studies that determined such a CF1 fitted

a linear regression through their data. However, an exponential

function is likely to be biologically more meaningful and

physiologically more realistic than a linear function, because it

predicts that the amount of prey consumed by a carnivore to

excrete one scat reaches an asymptote at large prey sizes (Fig. 2).

Such a maximum is reasonable because the total amount of food

a carnivore can consume of a large prey is limited and the ratio of

indigestible to digestible matter that is consumed does not change

after reaching this limit. In line with this, the apparent digestibility

increased with increasing prey body mass and reached an upper

limit.

Our results show that the consumed prey mass to excrete one

collectable scat reaches an asymptotic upper limit at a prey body

mass of approximately 50 kg (Fig. 2). Thus, when calculating the

diet as consumed prey mass per species there will be little effect on

the result whether prey remains of a large prey species in carnivore

scats are allocated to the weight of e.g. a heavy adult male, an

adult female or a juvenile of the species. This contrasts with the

application of a CF1 based on a linear function. If identified prey

species are allocated to prey sizes below 50 kg, such as newborns

of large prey species or any size class of small species, an accurate

assessment of prey body mass becomes important as this will have

an impact on the result for CF1 based on both linear and

exponential functions.

Figure 2. Correction factor 1 (CF1). Consumed mean prey mass (kg) per cheetah to excrete one collectable scat (Q5) as a function of mean prey body mass (kg) provided per feeding experiment (Q1). The curve represents CF1 and follows the exponential function y=2.358(1-exp(20.075x). The outlier of the warthog with 5.83 kg prey mass consumed to excrete one collectable scat (Table 1) was excluded from the analysis and figure. doi:10.1371/journal.pone.0038066.g002

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 6 June 2012 | Volume 7 | Issue 6 | e38066

T a b le

2 . A p p lic at io n o f co rr e ct io n fa ct o r 1 (C F1 , y = 2 .3 5 8 (1 -e xp

(2 0 .0 7 5 x) ) w it h x = Q 1 an

d y = Q 5 ) an

d co rr e ct io n fa ct o r 2 (C F2 ,y

= 3 .0 9 4 e xp

(2 0 .5 (l n (x /1 6 .3 7 0 )/ 2 .5 8 4 )2 ) w it h x = Q 1

an d y = Q 4 ) d e ri ve d fr o m

th e ch e e ta h fe e d in g e xp

e ri m e n ts

fr o m

th is st u d y to

a h yp

o th e ti ca l e xa m p le

o f 1 0 0 co lle ct ab

le sc at s b as e d o n a re g u la r sa m p lin

g sc h e m e , i.e . co lle ct e d

sc at s w e re

d e p e n d e n t o b je ct s.

Q 1

n Q 5

n6 Q 5

Q 4

n /Q

4 n6

Q 5 /Q

P re y

S ca

ts w it h

p re y h a ir

C o n su

m e d m a ss

to e x cr e te

1 sc a t

C o n su

m e d m a ss

to e x cr e te

n sc a ts

N o . o f e x cr e te d sc a ts

p e r

co n su

m e d p re y

C o n su

m e d in d iv id u a ls

to e x cr e te

n sc a ts

C o n su

m e d in d iv id u a ls

to e x cr e te

n sc a ts

N e w

m e th

o d

C o n v e n ti o n a l m e th

o d

S p e ci e s

A g e cl a ss

K g

n %

K g

% n sc a ts

n in d iv id u a ls

% n in d iv id u a ls

K u d u

ju ve n ile

1 0 0 .0 a

1 0

2 .3 6

2 3 .5 7

1 6 .0 4

2 .4 2

4 .1 3

9 .8 8

0 .2 4

2 .3 8

H ar te b e e st

ju ve n ile

6 7 .5 a

1 0

2 .3 4

2 3 .4 3

1 5 .9 5

2 .6 6

3 .7 6

8 .9 9

0 .3 5

3 .5 1

G o at

ad u lt

4 3 .0 b

1 0

2 .2 6

2 2 .6 4

1 5 .4 1

2 .8 9

3 .4 7

8 .2 9

0 .5 3

5 .3 2

Sp ri n g b o k

ad u lt

3 9 .0 a

1 0

2 .2 3

2 2 .3 1

1 5 .1 9

2 .9 2

3 .4 2

8 .1 8

0 .5 7

5 .7 8

D u ik e r

ad u lt

1 8 .0 a

1 0

1 .7 5

1 7 .4 7

1 1 .8 9

3 .0 9

3 .2 3

7 .7 4

0 .9 7

9 .8 0

G e m sb o k

ca lf

1 5 .0 a

1 0

1 .5 9

1 5 .9 2

1 0 .8 4

3 .0 9

3 .2 3

7 .7 4

1 .0 6

1 0 .7 2

St e e n b o k

ad u lt

1 1 .0 a

1 0

1 .3 2

1 3 .2 5

9 .0 2

3 .0 6

3 .2 7

7 .8 2

1 .2 0

1 2 .1 6

Sp ri n g h ar e

ad u lt

3 .5 c

1 0

0 .5 4

5 .4 4

3 .7 1

2 .5 9

3 .8 6

9 .2 4

1 .5 6

1 5 .7 1

W ar th o g

p ig le t

1 .2 a

1 0

0 .2 0

2 .0 3

1 .3 8

1 .8 6

5 .3 9

1 2 .8 9

1 .6 9

1 7 .0 8

Sq u ir re l

ad u lt

0 .5 c

1 0

0 .0 9

0 .8 7

0 .5 9

1 .2 4

8 .0 4

1 9 .2 3

1 .7 4

1 7 .5 3

D ie t co m p o si ti o n is p re se n te d as

fr e q u e n cy

o f p re y o cc u rr e n ce

(n ), co n su m e d m as s (n 6 Q 5 ), an

d co n su m e d n u m b e r o f p re y in d iv id u al s b as e d o n th e n e w

m e th o d (n /Q

4 ) an

d th e co n ve n ti o n al

m e th o d (n 6 Q 5 /Q

1 ). N o te

th e

d if fe re n ce s in

th e p ro p o rt io n s o f th e co n su m e d n u m b e r o f p re y in d iv id u al s b e tw

e e n th e n e w

an d th e co n ve n ti o n al

m e th o d . Fo

r d e ta ils

se e te xt . a d at a fr o m

[3 2 ],

b d at a fr o m

[2 ],

c d at a fr o m

[3 3 ].

d o i:1 0 .1 3 7 1 /j o u rn al .p o n e .0 0 3 8 0 6 6 .t 0 0 2

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 7 June 2012 | Volume 7 | Issue 6 | e38066

Correction Factor 2 If scats collected in the field arise from one feeding event

(dependent objects). In this study, we developed a new CF2

that we suggest is applied when carnivore diet is expressed in terms

of the proportion of consumed numbers of individuals per prey

species and when scats in the field are collected on a regular basis.

This correction factor considers that a large carnivore often does

not consume the entire prey animal but only part of it [1,2,5,22].

The application of CF2 in a hypothetical example demonstrated

that the number of animals per large prey species actually

consumed is substantially underestimated by the conventional

method (Table 2). This discrepancy increased with increasing prey

body mass (Table 2). As with CF1, a precise allocation of prey

remains in carnivore scats to age or sex classes is less important for

large than for small prey species. This is because CF2 first steeply

increases at small to medium prey body masses and subsequently

slowly decreases (Fig. 3). The slow decrease of CF2 with increasing

prey body mass implies that with increasing body mass a de-

creasing amount of indigestible prey parts is consumed, resulting

in a decreasing number of collectable scats. This might either be

a consequence of the carnivore feeding more selectively on

carcasses with a large body mass (particularly if feeding group size

is small and/or the carnivore does not return to feed repeatedly on

the same carcass as is the case in cheetahs [22]), or a change in the

characteristics of indigestible body parts such as fur if larger prey

individuals have shorter and less dense fur than medium sized

prey. The latter would mean that the ratio of indigestible fur to

digestible matter decreases with increasing prey size, resulting in

a peak at medium sized prey. To our knowledge, there are

currently no data on fur characteristics available from prey species

from southern Africa to test this idea.

Determination of the diet composition based on the number of

consumed individuals per species has two key applications: in

ecology it provides evidence on the possible impact of carnivore

predators on their prey, and in conservation biology it is important

information in the context of human-predator conflicts [2,13]. If

there is little information on age classes of killed prey or if the

particular carnivore species in question shows no preference for

a particular age class, it seems prudent to determine the diet

composition with at least two different prey body mass assess-

ments. This will provide a range of values for the number and

proportions of individuals consumed and will make the assessment

of the diet robust with respect to both ecological impact and

conflict issues.

For very small prey species a particular problem arises. Our

results indicate that for such prey animals the consumption of one

prey individual will not produce an entire scat (Fig. 3). The

smallest prey body mass to produce a complete scat (y=Q4) was

0.337 kg (x=Q1). Cheetah scats with remains of prey with a body

mass below this threshold will therefore consist of remains from

two consumed individuals of this particular species. Thus, the

number of consumed individuals for such prey should be

multiplied by a factor of 2.

Scats containing remains of different prey species are likely to

change their shape and consistency at different rates, which bias

the likelihood of collecting scats containing remains of particular

Figure 3. Correction factor 2 (CF2).Mean number of collectable scats excreted per cheetah and prey animal (Q4) as a function of mean prey body mass (kg) provided per feeding experiment (Q1). The curve represents CF2 and follows the peak logarithmic normal function y=3.094exp(20.5(ln(x/ 16.370)/2.584)2). The outlier of the warthog with a mean of 1.00 collectable scats per cheetah and prey animal (Table 1) was excluded from the analysis and figure. doi:10.1371/journal.pone.0038066.g003

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 8 June 2012 | Volume 7 | Issue 6 | e38066

T a b le

3 . D e te rm

in at io n o f th e co n su m e d n u m b e r o f p re y in d iv id u al s in

a h yp

o th e ti ca l e xa m p le

o f 1 0 0 co lle ct ab

le sc at s b as e d o n C F1

an d C F2

d e ri ve d fr o m

th e ch e e ta h fe e d in g

e xp

e ri m e n t o f th is st u d y.

P re y

C o n su

m e d n u m b e r o f p re y in d iv id u a ls

Q 1

n n /Q

4 /Q

2 n

S ca

ts w it h p re y

h a ir

S a m p le s co

ll e ct e d a s d e p e n d e n t o b je ct s (m

o re

th a n o n e

sc a t fr o m

e a ch

fe e d in g e v e n t)

S a m p le s co

ll e ct e d in d e p e n d e n tl y fr o m

e a ch

o th

e r (o n e

sc a t p e r fe e d in g e v e n t)

S p e ci e s

A g e cl a ss

K g

n S o li ta ry

M e a n g ro

u p si z e

S o li ta ry

M e a n g ro

u p si z e

T w o

F o u r

T w o

F o u r

K u d u

ju ve n ile

1 0 0 .0 a

1 0

4 .1 3

2 .0 7

1 .0 3

1 0

H ar te b e e st

ju ve n ile

6 7 .5 a

1 0

3 .7 6

1 .8 8

0 .9 4

1 0

G o at

ad u lt

4 3 .0 b

1 0

3 .4 7

1 .7 3

0 .8 7

1 0

Sp ri n g b o k

ad u lt

3 9 .0 a

1 0

3 .4 2

1 .7 1

0 .8 5

1 0

D u ik e r

ad u lt

1 8 .0 a

1 0

3 .2 3

1 .6 2

0 .8 1

1 0

G e m sb o k

ca lf

1 5 .0 a

1 0

3 .2 3

1 .6 2

0 .8 1

1 0

St e e n b o k

ad u lt

1 1 .0 a

1 0

3 .2 7

1 .6 4

0 .8 2

1 0

Sp ri n g h ar e

ad u lt

3 .5 c

1 0

3 .8 6

1 .9 3

0 .9 7

1 0

W ar th o g

p ig le t

1 .2 a

1 0

5 .3 9

2 .6 9

1 .3 5

1 0

Sq u ir re l

ad u lt

0 .5 c

1 0

8 .0 4

4 .0 2

2 .0 1

1 0

T h e ca lc u la ti o n s ar e sh o w n fo r tw

o sa m p lin

g sc h e m e s an

d th re e h yp

o th e ti ca lm

e an

si ze s o f fe e d in g g ro u p s. Q 4 is th e n u m b e r o f e xc re te d co lle ct ab

le sc at s p e r p re y in d iv id u al an

d ch e e ta h (s e e T ab

le 2 ) an

d Q 2 is fe e d in g g ro u p si ze .

Fo r d e ta ils

se e te xt . a , b , c se e T ab

le 2 .

d o i:1 0 .1 3 7 1 /j o u rn al .p o n e .0 0 3 8 0 6 6 .t 0 0 3

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 9 June 2012 | Volume 7 | Issue 6 | e38066

prey species and thus bias diet composition. For example, scats

from bobcats (Lynx rufus) containing deer remains experienced

a larger mass loss than scats containing mice and rats or rabbits

when left in the field for three weeks, reducing the likelihood for

scats containing deer to be reliably recognised as bobcat scats [30].

The choice of interval between collecting scats should therefore

ensure that a scat can be reliably allocated to the carnivore species

under study. Some carnivore species use latrines or special

marking places that might increase the chance of correctly

identifying scats of the studied carnivore. If such a sampling

scheme is not feasible, or several similar-sized carnivore species

feed on approximately the same prey community in an ecosystem,

then allocation of scats to consumer species may require the

application of molecular genetic methods to prevent this bias.

If scats collected in the field arise from independent

feeding events. If scats are collected from carnivores with

known individual identity and directly observed during defecation

or from immobilised individuals, and if the sampling interval is

longer than the time period over which a carnivore excretes scats

after having fed from one prey animal, each scat represents

a separate feeding event. As a consequence, diet composition

estimates differ from the previous sampling scheme by Q4 and for

carnivores feeding in groups additionally by the factor Q2 (Table 3).

It is therefore important to adjust data analysis by sampling regime

and the average feeding group size of the carnivore.

More than One Prey Species per Scat Our hypothetical example is based on scats containing remains

of one prey species only. However, scats sometimes contain more

than one prey species. Studies that determined the dry mass or

volume of all prey remains in the scats use the proportions of dry

masses or volumes of the different species in the scats, sum these

proportions up and apply CF1 to determine the consumed mass

per prey species applied [5,10,18,31]. If no information on dry

mass or volume is available, we suggest to allocate equal Q5

contributions of the different prey species to the scats, as this is

likely to represent a mean Q5 contribution to the scats in

a reasonably large sample size. For example, if 10 scats contain

remains of prey species A and prey species B, the consumed mass

per prey species in a solitary carnivore should be calculated as

(106Q5A60.5) + (106Q5B60.5). Similarly, to calculate the

consumed number of individuals per prey species we suggest to

allocate equal Q4 contributions of different prey species to the

scats. Using the same example, the consumed number of

individuals per prey species would be (10/Q4A60.5) + (10/

Q4B60.5).

Determination of CF1 and CF2 from Other Studies Feeding experiments have been conducted for other carnivores

such as the wolf [7–9], cougar [6] and Eurasian lynx [16]. All these

studies recorded the preymass of the prey animals provided, the prey

mass consumed by the carnivores, the number of scats produced by

the carnivores and the number of carnivores feeding from the prey

animals. With this information CF1 and CF2 can be derived in

retrospect and used for future diet determinations without the need

to repeat the feeding experiments. We reanalysed published raw

data of feeding experiments with wolves in North America [8],

Europe [9] and India [7], andwith Eurasian lynxes [16] by following

the steps presented inTable 1 to determineCF1 andCF2 (Table S1).

For all four studies, we fitted an exponential function to derive CF1

(wolf in North America: y=1.798(1-exp(20.008x); in Europe:

y=0.621(1-exp(20.012x); in India: y=1.382(1-exp(-0.020x); lynx:

y=1.045(1-exp(20.145x)). We also fitted an exponential function

through the data from the four studies to derive CF2 (wolf in North

America: y=37.311(1-exp(20.021x); in Europe: y=39.473(1-

exp(20.061x); in India: y=13.940(1-exp(20.980x); Eurasian lynx:

y=6.995(1-exp(20.201x)), however, the data from the study on

wolves in India were best described by a peak logarithmic normal

function with three parameters (y=21.792exp(20.5((ln(x/6.444))/

1.273)2)), similar to our cheetah study (calculations and figures in

Table S1).

Our results for CF2 suggest that the appropriate function to

derive CF2 differs between carnivores living in temperate and

tropical areas. Whereas CF2 reaches an asymptote in temperate

areas, CF2 in India and Namibia first steeply increased at small to

medium prey body masses and subsequently decreased slowly

(Fig. 3 and Table S1). Either large prey animals in tropical areas

have shorter or less dense fur than medium-sized prey animals

whereas in temperate areas this is not the case, or tropical

carnivores feed more selectively from larger prey, feed in smaller

groups or are less likely to return to a carcass than temperate

carnivores.

Application of CF1 and CF2 to Other Studies The application of CF1 and CF2 for cheetahs established by our

study to another study on cheetah diet in Namibia based on scat

analyses [2] revealed, as expected from the hypothetical example in

Table 2, a higher number of larger and a lower number of smaller

prey animals consumed than previously estimated (Table S2). The

new method indicated that 9.3% and 12.1% of the prey individuals

consumed by cheetahs in [2]’s study were livestock (cattle and sheep)

and hares, respectively, whereas the conventional method suggested

3.7% and 40.4%. Thus, cheetahs had a 2.5 times higher proportion

of livestock animals and a 3.3 times lower proportion of hares in their

diet than previously thought. Underestimation of predator-human

conflict on the basis of inaccurate consumption data is likely to

reduce the efficiency of management measures by farmers to reduce

the conflict or of conservation measures to mitigate such conflicts.

As far as we are aware, feeding experiments have not yet been

conducted for carnivores such as the tiger (Panthera tigris), leopard

(Panthera pardus) or dhole (Cuon alpinus) in India. We determined the

diet of these carnivore species in terms of consumed prey mass and

number of prey individuals (Table S2) by applying CF1 and CF2

derived from our cheetah feeding experiments for tiger and

leopard and from feeding experiments with Indian wolves (Table

S1) for the dhole. Compared to estimates based on the

conventional method [13], the number of larger prey was higher

and the number of smaller prey lower, predator pressure on gaur

(Bos gaurus) and sambar (Cervus unicolor) was between 1.7 and 2.2

times higher, and chital (Axis axis) was the main prey only for

leopard and dhole, overriding previous assessment of niche

overlap and predator-prey relationships (Table S2).

With all the reservations that apply when approximating the

diet of one predator with correction factors derived from another

predator, we still consider this a worthwhile approach. In essence,

this implies that the error introduced by transferring estimates of

correction factors between species is less than leaving the two

correction factors out altogether. For instance, the peak number of

collectable scats per individual wolf and prey animal was 21.8

(India) and 37.3 (North America) and 39.5 (Europe) (Table S1);

similar peak numbers for lynx in Europe was 7.0 (Table S1) and

for the cheetahs in this study 3.1. If applied within the same

geographical area and taxon, these differences are less substantial

than the corrections that resulted from comparing the cheetah

studies (2.5 and 3.3 fold changes in consumed numbers of livestock

animals and hares). Hence, if no CFs are available for the studied

species we suggest to apply (1) the cheetah CF1 and CF2 derived

in this study to Felidae of similar or larger size in hot and tropical

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 10 June 2012 | Volume 7 | Issue 6 | e38066

areas, (2) the wolf CF1 and CF2 derived from studies in North

America, Europe and India to Canidae from the respective

geographical areas and (3) the Eurasian lynx CF1 and CF2 to

Felidae of similar size in temperate areas. Such approximations

also need to consider the actual mean sizes of feeding groups of the

species under study and correctly identify the sampling scheme

used to collect scats (Table 3).

CF1 and CF2 determined in this study are only applicable to

carnivores feeding chiefly on mammalian prey species and on

species that are not completely consumed. For carnivore species

mainly feeding on fruits, invertebrates, birds and small mammals

such as black-backed jackals, side-striped jackals and red fox, the

diet should be determined using the specific conversion factors for

these food items [18,19,20,21] and following the guidelines in [20].

If small mammals are not completely consumed, CF2 can be

derived from the mammalian data of such feeding experiments

following the new method. For felids and canids in geographical

areas not covered by the CF1s and CF2s presented and suggested

here, new feeding experiments should be conducted.

Feeding Experiments The design of the feeding experiments will influence the

outcome in terms of the non-linear functions for CF1 and CF2.

How much and which parts of a prey animal a carnivore

consumes depends on factors such as its state of hunger, the prey

mass provided and competition with conspecifics [15,22]. There-

fore, if CF1 and CF2 are applied to scats collected in the field,

feeding experiments should simulate as closely as possible natural

feeding situations (see Table S3). Although it might not be possible

to completely simulate the situation under free-ranging conditions,

the determination of CF2 is desirable because even a rough

approximation of this factor will considerably reduce the bias in

the number of consumed prey species produced by the conven-

tional method.

Supporting Information

Figure S1 Correction factor 2 (CF2) described as exponential function from our data set in table 1. Mean

number of collectable scats excreted per cheetah and prey animal

(Q4) as a function of mean prey body mass (kg) provided per

feeding experiment (Q1). CF2 follows the exponential function

y=2.654(1-exp(20.960x)), R2=0.705, P,0.05, n=14. For details

and comparison with CF2 described as a peak logarithmic

function see Figure 3.

(TIF)

Table S1 Determination of correction factors 1 (CF1) and 2 (CF2) from four published feeding experiments with the new method. We used the studies on wolves from

North America [8], Europe [9] and India [7] and Eurasian lynx

from Europe [16]. For each study we present in a table the

published data and our calculations to derive CF1 and CF2, and

the figures with the regression curves and the equations for CF1

and CF2.

(DOC)

Table S2 Application of correction factors 1 (CF1) and 2 (CF2) to four published studies on carnivore diet following the new method. We applied CF1 and CF2 derived

from our feeding experiments with cheetahs (Acinonyx jubatus) to

a cheetah study in Namibia [2], and a tiger (Panthera tigris) and

leopard (P. pardus) study in India [13], and CF1 and CF2 derived

in this study from a feeding experiment with Indian wolves [7] (see

Table S1) to a dhole (Cuon alpinus) study in India [13].

(DOC)

Table S3 Guidelines for feeding experiments to ensure the experiments simulate as closely as possible natural feeding situations.

(DOC)

Acknowledgments

We thank the Ministry of Environment and Tourism in Namibia for

permission to conduct the study and at AfriCat Foundation particularly C.

Conradie and D. Houghton for their cooperation and support. We are

grateful to all farmers that provided prey animals, to S. Apenburg, T.

Bohm, B. Brunkow, M. Geingob, F. Geiseb, S. Goerss, C. Keller, K.

Schröder, S. Thalwitzer and M. Zeitlow for assistance, and to R. Bshary

for support.

Author Contributions

Conceived and designed the experiments: BW ASB JM. Performed the

experiments: ASB JM MJ. Analyzed the data: BW ASB JM OPH HH.

Wrote the paper: BW. Edited the manuscript: ASB JM OPH MJ HH.

References

1. Jedrzejewski W, Schmidt K, Theuerkauf J, Jedrzejewska B, Selva N, et al. (2002)

Kill rates and predation by wolves on ungulate populations in Bialowieza

primeval forest (Poland). Ecology 83: 1341–1356.

2. Marker LL, Muntifering JR, Dickman AJ, Mills MGL, Macdonald DW (2003)

Quantifying prey preferences of free-ranging Namibian cheetahs. S Afr J Wildl

Res 33: 43–53.

3. Napolitano C, Bennett M, Johnson WE, O’Brien SJ, Marquet PA, et al. (2008)

Ecological and biogeographical inferences on two sympatric and enigmatic

Andean cat species using genetic identification of faecal samples. Mol Ecol 17:

678–690.

4. Mech LD (1970) The wolf: the ecology and behavior of an endangered species.

New York: Natural History Press.

5. Floyd TJ, Mech DL, Jordan PA (1978) Relating wolf scat content to prey

consumed. J Wildl Manage 42: 528–532.

6. Ackerman BB, Lindzey FG, Hemker TP (1984) Cougar food habits in Southern

Utah. J Wildl Manage 48: 147–155.

7. Jethva BD, Jhala YV (2004) Computing biomass consumption from prey

occurences in Indian wolf scats. Zoo Biol 23: 513–520.

8. Weaver JL (1993) Refining the equation for interpreting prey occurrence in gray

wolf scats. J Wildl Manage 57: 534–538.

9. Ruehe F, Buschmann I, Wameling A (2003) Two models of assessing the prey

mass of European ungulates from wolf scats. Acta Theriol 48: 527–537.

10. Ciucci P, Boitani L, Pelliccioni ER, Rocco M, Guy I (1996) A comparison of

scat-analysis methods to assess the diet of the wolf Canis lupus. Wildlife Biol 2:

37–48.

11. de Villa Meza A, Martinez Meyer E, Lópes Gonzáles CA (2002) Ocelot

(Leopardus pardalis) food habits in a tropical deciduous forest of Jalisco, Mexico. Am Midl Nat 148: 146–154.

12. Ansorge H, Kluth G, Hahne S (2006) Feeding ecology of wolves Canis lupus

returning to Germany. Acta Theriol 51: 99–106.

13. Andheria AP, Karanth KU, Kumar NS (2007) Diet and prey profiles of three

sympatric large carnivores in Bandipur Tiger Reserve, India. J Zool 273: 169–

175.

14. Lockie JD (1959) The estimation of the food of the foxes. J Wildl Manage 23:

224–227.

15. Rühe F, Ksinsik M, Kiffner C (2008) Conversion factors in carnivore scat analysis: sources of bias. Wildlife Biol 14: 500–506.

16. Rühe F, Burmester T, Ksinsik M (2007) Data for estimating eaten prey masses

from Eurasian lynx Lynx lynx scats in Central and East Europe. Acta Theriol 52: 317–322.

17. Wachter B, Jauernig O, Breitenmoser U (2006) Determination of prey hair in

faeces in free-ranging Namibian cheetahs with a simple method. Cat News 44: 8–9.

18. Goszczynski J (1974) Studies on the food of foxes. Acta Theriol 19: 1–18.

19. Atkinson RPD, Macdonald DW, Kamizola R (2002) Dietary opportunism in side-striped jackals Canis adustus Sundevall. J Zool 257: 129–139.

20. Reynolds JC, Aebischer NJ (1991) Comparison and quantification of carnivore

diet by faecal analysis: a critique, with recommendations, based on a study of the fox Vulpes vulpes. Mammal Rev 21: 97–122.

21. Loveridge AJ, Macdonald DW (2003) Niche separation in sympatric jackals (Canis mesomelas and Canis adustus). J Zool 259: 143–153.

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 11 June 2012 | Volume 7 | Issue 6 | e38066

22. Caro T (1994) Cheetahs of the Serengeti plains: group living in an asocial

species. Chicago: University of Chicago Press. 478 p.

23. Eaton RL (1974) The cheetah: the biology, ecology, and behavior of an

endangered species. New York: van Nostrand Reinhold.

24. Mills MGL (1984) Prey selection and feeding habits of the large carnivores in the

southern Kalahari. Koedoe 27: 281–294.

25. Marker-Kraus L, Kraus D, Barnett D, Hurlbut S (1996) Cheetah survival on

Namibian farmlands. Windhoek: Cheetah Conservation Fund.

26. Radloff FGT, du Toit JT (2004) Large predators and their prey in a southern

African savanna: a predator’s size determines its prey size range. J Anim Ecol 73:

410–423.

27. Mills MGL, Broomhall LS, du Toit JT (2004) Cheetah Acinonyx jubatus feeding

ecology in the Kruger National Park and a comparison across African savanna

habitats: is the cheetah only a successful hunter on open grassland plains?

Wildlife Biol 10: 177–186. 28. Pienaar UdV (1969) Predator-prey relationships amongst the larger mammals of

the Kruger National Park. Koedoe 12: 108–176.

29. Robbins CT (1993) Digestion and nutrient metabolism. In: Robbins CT, editor. Wildlife feeding and nutrition. California: Academic Press. 288–322.

30. Godbois IA, Conner LM, Leopold BD, Warren RJ (2005) Effect of diet on mass loss of bobcat scat after exposure to field conditions. Wildl Soc Bull 33: 149–153.

31. Jedrzejewski W, Jedrzejewska B, Okarma H, Schmidt K, Zub K, et al. (2000)

Prey selection and predation by wolves in Bialowieza primeval forest, Poland. J Mammal 81: 197–212.

32. Bothma JdP (1989) Game ranch management. South Africa: Van Schaik. 33. Kingdom J (1997) The Kingdon Field Guide to African Mammals. San Diego:

Academic Press.

Diet Assessment in Carnivores Based on Scats

PLoS ONE | www.plosone.org 12 June 2012 | Volume 7 | Issue 6 | e38066