Quantifying Equid Behavior—

A Research Ethogram for Free-Roaming 

Feral Horses

U.S. Department of the Interior

U.S. Geological Survey

Techniques and Methods 2-A9
Cover photo by Jason Ransom.
Quantifying Equid Behavior—A Research 

Ethogram for Free-Roaming Feral Horses

By Jason I. Ransom and Brian S. Cade 

Techniques and Methods 2-A9

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, 

natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Ransom, J.I. and Cade, B.S., 2009, Quantifying equid behavior— A research ethogram for free-roaming feral horses: 

U.S. Geological Survey Techniques and Methods 2-A9, 23 p.
iii

Contents

Introduction.....................................................................................................................................................1

Background.....................................................................................................................................................1

Social Organization........................................................................................................................................1

Ethological Data Collection and Analyses.................................................................................................2

Ethogram .........................................................................................................................................................4

Feeding ...................................................................................................................................................4

Resting ...................................................................................................................................................4

Locomotion.............................................................................................................................................6

Maintenance..........................................................................................................................................6

Grooming.......................................................................................................................................6

Comfort ..........................................................................................................................................8

Standing Attentive .......................................................................................................................8

Elimination.....................................................................................................................................8

Social ................................................................................................................................................... 10

Harem Social ..............................................................................................................................10

Herding ........................................................................................................................................10

Harem Tending ...........................................................................................................................10

Reproduction ..............................................................................................................................10

Agonism.......................................................................................................................................16

Submission..................................................................................................................................20

Acknowledgments ......................................................................................................................................20

References....................................................................................................................................................21

Figures

1. Observed daytime activity budgets of adult control female feral horses and harem 

stallions in Colorado, Wyoming, and Montana, 2003–2006....................................................5

2. Feral horses grazing .......................................................................................................................5

3. Resting behavior in a band of feral horses.................................................................................6

4. Example of locomotion, most typically expressed as walking from one place to 

another ...........................................................................................................................................7

5. Rolling by a feral horse mare as a grooming behavior.............................................................7

6. Example of masturbation, a typical comfort behavior for feral horse males........................8

7. Feral horse mares focused on an external stimulus and exhibiting standing attentive 

behavior..........................................................................................................................................9

8. A band of horses exhibiting human awareness.........................................................................9

9. A female feral horse exhibiting elimination by urination........................................................10

10. Example of allogrooming (mutual grooming), one of the most common harem social 

behaviors............................................................................................................................................. 11

11. Olfactory investigation in the harem social behavior context...............................................11

12. Pair-bonding among juveniles within a band as a common harem social behavior.........12

13. A feral horse stallion herding females in his band..................................................................12
iv

14. A stallion harem tending, guarding females against an intruder male................................13

15. Male feral horse expressing harem tending by maintaining a fecal midden .....................13

16. Flehmen response in a feral horse stallion displayed by an elevated head and raised, 

inverted upper lip........................................................................................................................14

17. A feral horse stallion engaged in the male reproductive sequence ....................................15

18. Basic guidelines for distinguishing reproductive and non-reproductive stallion 

behaviors .....................................................................................................................................15

19. Successful copulation between a feral horse male and female ..........................................16

20. Agonism expressed by two feral horses in the form of a threat...........................................17

21. Example of pushing as an agonistic expression......................................................................17

22. Example of chasing as a moderately intense form of agonism.............................................18

23. Example of biting as a common expression of agonism.........................................................18

24. Example of rearing as an expression signifying a potentially intense agonistic 

interaction....................................................................................................................................19

25. Example of striking or stomping as typically indicative of highly agonistic expression ...19

26. Example of boxing and dancing between two stallions as illustrative of the highest 

level of agonism..........................................................................................................................20

27. Submission expressed by a young male horse, directed toward the larger, dominant 

male displaying threat behavior associated with dominance ............................................21


Introduction

Feral horses (Equus caballus) are globally distributed 

in free-roaming populations on all continents except Antarctica and occupy a wide range of habitats including forest, 

grassland, desert, and montane environments. The largest 

populations occur in Australia and North America and have 

been the subject of scientific study for decades, yet guidelines 

and ethograms for feral horse behavioral research are largely 

absent in the scientific literature. The U.S. Geological Survey (USGS) Fort Collins Science Center conducted research 

on the influences of the immunocontraceptive porcine zona 

pellucida (PZP) on feral horse behavior from 2003–2006 in 

three discrete populations in the American west (see Ransom and others, 2007; Ransom, 2009). These populations 

were the Little Book Cliffs Wild Horse Range in Colorado, 

McCullough Peaks Herd Management Area in Wyoming, and 

Pryor Mountain Wild Horse Range in Montana; the research 

effort included over 1,800 hours of behavioral observations of 

317 adult free-roaming feral horses. The following ethogram 

was developed during the course of this study to facilitate 

accurate scientific data collection on feral horse behavior, 

which is often challenging to quantify. By developing this set 

of discrete behavioral definitions and a set of strict research 

protocols, scientists were better able to address both applied 

questions, such as behavioral changes related to fertility 

control, and theoretical questions, such as understanding social 

networks and dominance hierarchies within social groups 

of equids.

Background

Feral horses in North America are descendents of animals 

that escaped domesticity or were intentionally released by 

settlers, explorers, and military personnel, and because of 

their highly adaptive nature were able to thrive in a multitude 

of environments. In the United States most feral horses are 

federally protected by the Wild Free-Roaming Horses and 

Burros Act of 1971, which refers to them as “living symbols of the historic and pioneer spirit of the West,” stating 

that “they contribute to the diversity of life forms within the 

Nation and enrich the lives of the American people” (Public Law 92-195, 85 Stat. 649, as amended). Roughly 30,000 

feral horses are distributed across 10 western States in the 

United States on 21.4 million ha of federally designated horse 

range. With annual population growth rates reported at 15–25 

percent (Eberhardt and others, 1982; Wolfe and others, 1989; 

Garrott and Taylor, 1990; Garrott and others, 1991) and very 

limited natural depredation, the influence of feral horses on 

native flora, fauna, and ecosystem processes varies greatly 

(see Smith, 1986; Fahnestock and Detling, 1999; Coughenour, 2002; Levin and others, 2002; Beever and Herrick, 2006; 

Beever and others, 2008). Understanding animal behavior can 

be an important tool in addressing a species’ influences and 

roles in an ecosystem and can lead to better management and 

conservation practices (Sutherland, 1998; Buchholz, 2007). 

Additionally, when management practices such as fertility 

control alter natural biological processes, it is important to 

consider the ethical implications, such as influences on animal 

behavior and social structure (Nettles, 1997; Asa and others, 

2005; Porton, 2005).

Social Organization

Feral horses arrange themselves in family groups known 

as bands, which range in size from 2 to 20 or more animals. 

Band size is variable and may be a response to both the environment the horses inhabit and population density. Animals 

can reduce risk of predation by living in groups (Pusey and 

Packer, 1997), and in open habitats without cover in which 

to hide, animals may form larger groups (Molvar and Bower, 

1994). The latter was found to be true in the USGS study, 

Quantifying Equid Behavior—A Research Ethogram for 

Free-Roaming Feral Horses

By Jason I. Ransom and Brian S. Cade
2 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

where mean band size in the sage steppe habitat found at 

McCullough Peaks was 8.01 ± 0.38 (SE) horses, while habitats with trees and dense vegetation had smaller mean band 

sizes—4.45 ± 0.16 horses at Little Book Cliffs and 4.16 ± 0.17 

horses at Pryor Mountain.

Feral horse bands typically consist of a single polygynous 

stallion, adult females, foals of the year, and yearling males 

and females. Bands with multiple stallions do occur and were 

first reported by Denniston (1979) and Miller (1979). Miller 

(1979) found that multiple stallions were present only in bands 

consisting of greater than 9.3 horses. This finding was supported by the USGS study, during which multiple-stallion 

bands were recorded only at McCullough Peaks; multiple 

stallions occurred in five bands of horses consisting of 9–18 

animals each. At 2 years of age, subordinate males typically 

disperse the band into bachelor groups of two to several 

horses, but occasionally 2- and 3-year-old males remain with 

the band if the stallion does not drive them away. Rutberg and 

Keiper (1993) found that the age at which male horse dispersal 

occurs is strongly correlated with the number of peers in the 

natal group. 

Feral horse bands are not geographically territorial and 

home ranges overlap with those of other bands in the population. This geographically non-territorial, harem-type social 

structure is known as Type I organization and also is used 

by the Przewalski horse (Equus ferus przewalskii), Plains 

zebra (Equus burchellii), and Mountain zebra (Equus zebra) 

(Klingel, 1975; Rubenstein, 1989). The other organizational 

structure found in equids, Type II organization, involves adult 

males establishing geographic territories and females moving 

between them. Type II organization is used by the Grevy’s 

zebra (Equus grevyi), African wild ass (Equus africanus), and 

Asiatic wild ass (Equus hemionus). While feral horses do not 

exhibit geographic territoriality, the USGS study did document 

resource-oriented territoriality whereby stallions (with the 

entire band present) defended mineral sources repeatedly and 

often with elevated agonistic interactions when other bands 

approached. 

Ethological organization within horse bands is characterized by a dominance hierarchy, but the literature has 

conflicting functional explanations for hierarchical structures 

in equids. Houpt and others (1978) found that body weight 

affected social rank but age did not; however, other researchers (Keiper and Sambraus, 1986; Rho and others, 2004; Heitor 

and others, 2006) found age to be linearly correlated with 

social rank. Reproductive status of females has been shown 

to influence their social dominance in a band, as well as their 

rate of interchange between bands (van Dierendonck and 

others, 2004). Most studies, however, indicate that agonism 

is strongly correlated with dominance rank among females 

(Houpt and others, 1978; Waring, 1983; Keiper and Receveur, 

1992; Weeks and others, 2000). The USGS study found that 

the most dominant members of feral horse bands were female, 

and stallion rank varied by band. This ethological structure is 

reported in much of the existing literature (Houpt and Keiper, 

1982; McCort, 1984; Keiper and Sambraus, 1986; Klimov, 

1988; and Keiper and Receveur, 1992). Lack of stallion 

dominance has been attributed to the amount of time stallions 

spend away from the band while recruiting new females or 

engaging in agonistic interactions with other stallions; females 

in a band, however, can establish stronger hierarchical relationships because they continuously remain in close proximity to one another (Keiper and Receveur, 1992). Social rank 

in bachelor groups, which are often unstable, has only been 

attributed to individual temperament (Tilson and others, 1988).

Ethological Data Collection and 

Analyses

It is possible to quantify behavior through the systematic 

enumeration of discretely defined categorical behaviors in 

terms of counts of occurrence or proportions of time exhibited. 

Collection of ethological data may be accomplished through 

several techniques, and the ultimate decision rests on the 

precisely defined research objectives. The reader is referred 

to Altmann (1974) for a definitive overview of sampling 

methodology for observational data. In the last 30 years, 

many insights have contributed to refining these methods, 

such as how to determine the appropriate time period between 

sampling when using the instantaneous scan sampling method 

and a better research design to capture infrequent behavioral 

expressions. In sampling feral horse behavior, the USGS study 

found that instantaneous scan sampling (the method of recording the categorical behavior of each focal animal at precise 

moments in time) at 1-min intervals was ideal for quantifying 

time budget data. Continuous sampling is an alternative to this 

technique and involves recording a focal animal’s behavior 

continuously and noting the point in time that a new behavior 

begins. Continuous sampling was impractical for our study 

due to the number of animals and observers involved. Mitlohner and others (2001) found no significant difference between 

behavioral data recorded with instantaneous scan sampling 

versus continuous sampling when intervals were 15 minutes 

or less, and found a high correlation between the techniques 

when using 1-min intervals. 

Collecting data on time budgets using instantaneous 

scan sampling is fairly straightforward, but behaviors that are 

infrequent and expressed briefly are not likely to be captured 

adequately (Houpt, 1991; Doran, 1992). Two relatively good 

options exist for collection of such data: the all-occurrence 

method and focal sampling. All-occurrence data collection 

records every behavior every time it is observed (Altmann, 

1974) and can be a good technique when the number of 

animals in the focal band is not too large and the behaviors 

of interest are easy to detect. Although less efficient in terms 

of data collection, the focal sample method may be more reliable since the observer’s focus is directed at only one animal 

(Altmann, 1974; Houpt, 1991). This method involves randomly selecting one individual in the band and continuously 

observing and recording all behavioral expressions. In feral 
Ethological Data Collection and Analyses 3

horse research, capturing briefly occurring expressions is most 

important for reproductive, social, and agonistic behaviors. 

Feeding, resting, and locomotion typically occur in periods 

long enough to be captured by most techniques.

Ethological protocols must be established prior to data 

collection and should be defined by research objectives. The 

discrete behavioral categories presented in this ethogram do 

not preclude the exhibition of simultaneous behaviors. For 

example, it is typical in feral horses for a comfort behavior 

such as masturbation to occur while the animal is feeding, so 

a protocol should be explicitly defined stating which behavior 

takes precedence in the data record. If the objective of your 

research is to determine the amount of time horses are feeding 

in relation to some covariate, then feeding is the appropriate 

category, and if expression of comfort behavior is the focus, 

then it should be recorded as such (or in this case, one might 

wish to subdivide comfort into several behaviors, since comfort is generally a short-duration behavior with many specific 

expressions). Regardless of the approach, notations of simultaneous occurrences are invaluable in retrospect. 

Simultaneous behavioral expressions are not the only 

observational data collection pitfall. Some behaviors, such as 

olfactory investigation, can be ascribed to several categories. 

This behavior may fall under comfort, reproduction, or harem 

social behavior, but the correct categorization of such expressions is not subjective: each expression does have an absolute 

definition. In such cases, the context of the behavior will 

define its true characterization. When such potentially confusing behaviors are prevalent, they are addressed specifically in 

the ethogram.

Considerably more in-depth analyses of behavior are possible when covariates associated with individual focal subjects 

are collected reliably. Many factors may influence behavior, 

such as age, body condition, dominance rank, presence of 

dependent foal, climate, and habitat. Fortunately, many feral 

horses have unique natural markings, making identification of 

individual animals possible without the use of radio-collars 

or numbered tags. Pelage color; facial patterns such as snips, 

strips, blazes, and stars; and leg markings such as coronet 

bands, socks, and stockings collectively make cataloging and 

referencing study animals feasible (Sponenberg and Beaver, 

1992; Gower, 2000; Green 2001). Properly cataloging and 

identifying individual horses in a research effort can provide 

the foundation from which to build in-depth covariate data and 

thus lead to a better understanding of animal behavior. 

Analyses of behavioral data may incorporate many traditional statistical methods, but time budget data presents a particularly challenging dilemma. These analyses must consider 

the compositional nature of a time budget: models exhibiting strong support for one behavioral category must also be 

considered for each other category. Proportions of time spent 

in behavioral categories are compositional dependent variables 

because the sum of the proportions in all behavioral categories sum to 1. In other words, there is a unit sum constraint 

(Aitchison, 1986) by which more time spent in one or more 

behavioral categories must be associated with less time spent 

in one or more other behavioral categories. These compensatory shifts in estimates are absolute, leading to a dependent 

relationship among behaviors constituting the time budget 

being analyzed (Elston and others, 1996). Many compositional 

data-analysis procedures have been developed (for example, 

log-ratio procedures; Aitchison, 1986, 1992), but few are 

appropriate for data that exhibit real values of 0 or 1. It may be 

important that the amount of time an animal exhibits a given 

behavior is truly 0 percent or 100 percent. Many methods, 

such as log-ratio analysis, require data transformations that 

eliminate values of 0 and 1 by assigning very small or very 

large values (greater than 0 or less than 1) (Bakeman and others, 1992; Clark and Messina, 1998). This process ultimately 

alters the distribution of data and may adversely affect conclusions drawn about individual behaviors in the composition 

(Bingham and Brennan, 2004). Once transformed, the common method of log-ratio analysis also produces only quantitative statements about the overall distribution of the composition in comparison to another and the sampling distribution 

of the difference; it does not specify explicit contributions of 

each piece of the composition to those differences (Aitchison, 

1986). If your data are not composed of real values of 0 and 

1, log-ratio analyses may be appropriate. It is best suited for 

compositions with only two elements since conclusions about 

the change in allocation may be drawn easily (Elston and others, 1996), but most behavioral studies aim to address multiple 

behaviors. Some extensions of the algebra of log-ratio compositional measures have been made by Billheimer and others 

(2001), but currently these procedures are limited to three-part 

compositions and still suffer the restriction of not allowing 

zero proportions.

One solution to the problem of comparing time-budget 

compositions with several behaviors and true values of 0 and 1 

is the use of a multi-response permutation procedure (MRPP; 

Mielke and Berry, 2007). This method does not require datatransformation and analyzes compositional differences by 

approximating probabilities of a test statistic based on average 

Euclidean distances for detecting distributional differences. In 

other words, the test is focused on differences in multivariate 

cumulative distributions rather than means. This approach 

may yield useful results for drawing conclusions about how 

different animals or treatment groups allocate their time, but 

it still does not provide insightful conclusions about specific 

behaviors within the composition of interest. No standardized way to approach this problem currently exists, but one 

solution is simply to model each behavior to query further 

covariates and relationships of interest: analyze each part of 

the behavioral composition as a univariate dependent variable. 

For such results to be interpretable, however, the same models 

must be applied and presented for all individual behaviors in 

the composition. 

In simple compositions with few behaviors, the trade-off 

in time allocation may be evident. It is likely, however, that 

such clear trade-offs will not always be evident and multiple 

models must be presented for each behavior. For example, 

consider a simple composition of three horse behaviors 
4 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

(Yf = feeding, Yr = resting, and Yl = locomotion, where Yf + Yr

+ Yl = 1.0). If Yf has a strong linear increase with the predictor 

variable X1 (for example, 0/1 indicator variable of sex) and a 

weak linear increase with predictor variable X2 (for example, 

herd size), then Yr , Yl , or both must decrease with X1, but 

the actual magnitude of that decrease will depend on both 

behaviors and the degree to which they also are influenced 

by X2 (model 1 is Y = f(X1 + X2)). It could easily be that the 

strongest model for Yr might include X2 and another predictor 

(say X3, and model 2 is Y = f(X1 + X3)). Thus, it is possible 

for model 1 to be strongly selected for analyzing the Yf part 

of the Y compositional vector of behaviors but model 2 to be 

strongly selected for the Yr part of the composition. Likewise, 

one model may be strongly supported for several behaviors 

and a complement model may be strongly supported for the 

remaining behaviors in the composition (see Ransom, 2009); 

however, because the behavioral composition really induces 

a relationship among the parts of the composition, statistical 

model results will be uninterpretable if a selected model is not 

considered to apply to all parts of the behavioral composition 

(for example, Yf

 , Yr, and Yl). 

The increasing use of maximum-likelihood and Bayesian approaches for solving complex problems may ultimately 

lead to the development of more lucid guidelines for many 

problems indicative of behavioral data. These methods can 

provide powerful tools for analyzing scientific data and can 

lead to a deeper understanding of the processes and errors 

involved (Hobbs and Hilborn, 2006). Regardless of the 

statistical approach, the path toward proper model selection 

for individual dependent behaviors in a composition has not 

been described in the literature. The use of model weights and 

model averaging may assist in drawing coherent conclusions 

about parameters of interest (Burnham and Anderson, 2002), 

but all supported models must be considered simultaneously 

for all dependent compositional variables to avoid violating 

the inherent statistical assumptions. A reasonable approach 

to assessing strength of evidence for compositional models, 

without violating assumptions of dependence, is to sum the 

minimum Akaike’s Information Criteria (AIC: Burnham and 

Anderson, 2002) scores for the individually-modeled constituent behaviors in a composition; subsequently, each sum then 

forms an aggregate AIC score for each compositional model. 

The strength of evidence for the overall composition may then 

be assessed using AIC weights as Burnham and Anderson 

(2002) describe for individual models.

Ethogram

This ethogram was developed to investigate the influences of fertility control on feral horse behavior; thus, the 

behavioral groupings are broad in some contexts, such as 

feeding behavior, and much more detailed in areas of specific 

interest to the research objectives, such as agonism. Behavioral researchers often consolidate an array of behavioral 

expressions into broad categories since data collection on 

every specific behavior expressed is usually impractical and 

makes analyses excessively difficult. Therefore, this ethogram 

divides behavioral expressions into 13 discrete categories that 

cover the range of expressions a feral horse may exhibit in 

free-roaming conditions. Two additional categories (human 

awareness and out-of-sight) are used to account for biased 

observations. These 13 categories can easily be further aggregated a posteriori if desired, but categorizing these behaviors separately a priori allows for a wider range of possible 

analyses while still being practical for data collection. An 

example of a broader aggregation of these categories is the 

consolidation of grooming, comfort, standing attentive, and 

elimination into maintenance; herding, reproduction, harem 

tending, harem social, agonism, and submission into social; 

and human awareness and out-of-sight (unavailable to the 

observer) into unknown (fig. 1). At any given time during the 

course of observation, a focal animal will be exhibiting behavior that can be described by one of these categories. Developing a research ethogram from the several hundred behavioral 

expressions documented in equids can be a daunting task; 

therefore, this basic ethogram for feral horses is presented as a 

starting point for behavioral studies. For an excellent ethogram 

resource detailing complete equid behavior expressions, the 

reader is referred to McDonnell (2003). For a comprehensive 

work on equine behavior, the reader should also see Waring 

(1983).

Feeding

Feeding behavior occupies roughly half of the daily 

time budget of feral horses (fig. 1) and usually entails grazing. Grazing occurs as a horse bites off and ingests grasses 

and forbs close to the ground (fig. 2). The feeding category 

also includes browsing on woody plants and trees, eating 

snow, drinking, mineral licking, coprophagy (eating feces), 

and pawing at food resources. The latter is critical in defining 

feeding as a mutually exclusive category in that a horse may 

be pawing at soil, plants, or snow, but if the action is directly 

related to acquiring and ingesting a food resource, then it 

should be considered as feeding behavior. Also, horses move 

as they graze; therefore, as long as the horse is feeding while 

it is moving, it should be considered as feeding rather than 

locomotion. 

Resting

The second largest amount of time in the daily time 

budget of feral horses is allocated to resting, which may occur 

during 25–35 percent of the daylight hours (fig. 1). Resting 

behavior is characterized by a general lack of attention and 

relaxed state and may occur in a standing position or in recumbency (fig. 3). This includes both relaxation and sleeping. 

Horses are able to sleep standing up due to the stay apparatus 

that allows their body to be supported without active muscular 

control (Dallaire, 1986). This behavior is typically observed 
Ethogram 5

Figure 1. Observed daytime activity budgets of adult control female feral horses (n = 207, mean age = 7.79 yrs ± 0.33 SE, 

range = 2–21 yrs) and harem stallions (n = 110, mean age = 11.63 yrs ± 0.43 SE, range = 5–26 yrs) at Little Book Cliffs Wild 

Horse Range in Colorado (LBC), McCullough Peaks Herd Management Area in Wyoming (MCP), and Pryor Mountain Wild 

Horse Range in Montana (PRY), 2003–2006.

0

10

20

30

40

50

60

70

80

90

100

LBC Females

LBC Stallions

MCP Females

MCP Stallions

PRY Females

PRY Stallions

Unknown

Social

Maintenance

Locomotion

Resting

Feeding

PERCENT OF DAYLIGHT HOURS 

Figure 2. Feral horses grazing, the most typical feeding behavior. 
6 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

as a body position with the head lowered, eyes closed, and one 

rear foot slightly elevated. Resting behavior in a band is often 

characterized by huddling, which facilitates insect control 

by the tail-swishing of close neighbors. Recumbent rest can 

be sternal or lateral. The comfort behavior of sun-basking is 

expressed in a laterally recumbent state, so a protocol must 

be defined a priori characterizing this state as rest or comfort, 

based on research objectives.

Locomotion

The third largest amount of the daily time budget is 

spent on locomotion. This behavior includes walking, trotting, cantering, galloping, jumping, and swimming and in 

feral horses is typically used for moving from one resource to 

another (fig. 4). Since most feral horse populations in North 

America occupy arid or semi-arid environments, movement 

to the few and scattered water sources is often the impetus for 

daily occurrences of extended locomotion (typically every 12 

to 24 hrs). Otherwise, feral horses do not expend vast amounts 

of energy in locomotion, with the exceptions of brief social 

interactions between bands, stallion agonistic expressions, 

and female recruitment efforts by stallions. In this ethogram, 

locomotion integral to reproductive, harem tending, or comfort behaviors is considered part of its respective behavioral 

expression and not recorded as locomotion.

Maintenance

Grooming

Grooming behavior occupies a relatively small but 

important part of the daily time budget of feral horses and is 

often observed as rolling. Rolling occurs both on land and in 

water and is thought to assist with pelage health and insect 

control (fig. 5) (Waring, 1983). Other grooming behaviors 

include shaking, nibbling or licking on self, tail-swishing, 

rubbing, and periodic stomping to displace flies and biting 

insects. Allogrooming (also known as mutual grooming) in 

this ethogram is not considered categorically as a grooming 

behavior since it is also a social interaction that involves more 

than one animal. Depending on the nature of the research, it 

may be appropriate to consider allogrooming as part of the 

grooming category.

Figure 3. Resting behavior in a band of feral horses is often characterized by huddling. Aside from the physical protection 

received by this behavior, the head-to-tail orientation of band members in this type of resting behavior also facilitates grooming. 

This allows for insect control around the head by the tail-swishing effect of neighbors.
Ethogram 7

Figure 4. Locomotion is most typically expressed as walking from one place to another, as seen in this feral horse stallion. The 

higher energy-expense gaits of trotting, cantering, and galloping are observed far less frequently. 

Figure 5. Rolling by this feral horse mare is a grooming behavior associated with pelage hygiene and insect control.
8 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

Comfort

Comfort behavior takes on a wide variety of forms in 

feral horses and includes any type of self-enjoyment expression, such as play, investigation, and stimulation (fig. 6). Some 

examples of comfort behavior are sun-basking, shelter seeking, masturbation, sexual play, object play, locomotor play, 

play fighting, and some olfactory investigations. Olfactory 

investigations also may be indicative of reproductive behavior 

or social behavior and should be included in the appropriate 

category for data collection based on specific research objectives. This ethogram also includes yawning and stretching as 

comfort behaviors, though it would not be inappropriate to 

include those expressions as a form of resting behavior.

Standing Attentive

When horses receive a stimulus that causes alertness, 

they react by exhibiting a rigid body posture with head 

upright, ears pointed forward, and eyes open and alert (fig. 

7). This may be momentary in the case of a sound or smell 

causing alertness, but such standing attentive behavior also 

occurs for extended periods of time when a female is standing 

guard over a sleeping foal or a predator is nearby. In this ethogram, standing attentive does not include instances when the 

behavior is a result of human presence (fig. 8). In those cases, 

human awareness is considered its own category so that the 

biased data may be properly addressed during analyses.

Elimination

Elimination in horses is expressed as urination or defecation (fig. 9), though depending on research objectives, it 

should be determined whether any such expression will be 

included in this category or whether elimination with social 

implications is considered elsewhere. Socially, feral horse 

stallions create fecal middens known as stud piles and repeatedly defecate on them. These middens are thought to facilitate 

communication or ownership status of certain resources (Feist 

and McCullough, 1976; Rubenstein and Hack, 1992). When 

female feral horses urinate or defecate, it is common for the 

harem stallion to cover it with his urine for similar reasons. It 

has been reported that female horses do not cover the urine of 

other females in this fashion (McDonnell, 2003), though this 

was documented periodically during our study and may have 

implications in the female dominance hierarchy. 

Figure 6. A typical comfort behavior for feral horse males is masturbation, which is expressed when a horse flexes his erect 

penis against his abdomen. This behavior is not expressed in conjunction with a nearby female and should not be confused 

with the penis drop observed when a male is reproductively tending a female.
Ethogram 9

Figure 7. Feral horse mares are focused on an external stimulus (in this case, a foal distress vocalization in the distance) 

and are exhibiting standing attentive behavior. Note the directionally pointed ears, rigid body position, and focused eyes 

characteristic of this expression. This behavior should not be confused with human awareness.

Figure 8. Human awareness is an important behavior to record when conducting any behavioral research so that biased 

data can be properly omitted from analyses of naturally occurring behaviors. Here, an entire band has paused because they 

noticed the photographer in the distance. 
10 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

In this ethogram, random urination and defecation are 

considered elimination, whereas systematic covering of urine 

or feces from the female by a harem stallion is considered as 

a harem tending behavior. The systematic covering of urine 

from a female by a female in the same harem is considered 

harem social behavior.

Social 

Harem Social

Harem social behavior is considered to be social interaction among band members that is not specifically indicative 

of reproductive, harem tending, or agonistic behavior. Allogrooming is considered a harem social behavior in this ethogram (fig. 10), as is olfactory investigation (from one horse to 

another, fig. 11, or the systematic smelling of urine deposits 

among band members) and pair-bonding among juveniles 

(fig. 12).

Herding

When a feral horse stallion actively drives females of 

his harem together, it is considered herding behavior. This 

involves the stallion moving systematically behind the 

females, posturing with his head held low and ears laid back, 

and controlling the direction and movement of the band members (fig. 13). Waring (1983) termed this motion with the stallion’s head moving side-to-side as snaking. Some researchers 

may choose to consider this as an agonistic behavior, but it 

is considered here as its own category since the function of 

the behavior is maintaining the harem rather than aggression 

toward specific females. 

Harem Tending

Harem tending consists of stallion behaviors that are 

directed at maintaining the harem and include the defense and 

recruitment of females. The defense of females is expressed as 

a stallion positioning himself between his harem females and a 

perceived threat (typically another stallion) (fig. 14). It is also 

expressed by covering a female’s urine or feces with his own, 

or by depositing feces on a stud pile (fig. 15). Recruitment, or 

stealing, of females by a harem stallion from another stallion 

is also considered harem tending behavior in this ethogram.

Reproduction

Reproductive behavior in feral horses is characterized by 

a series of stallion-initiated behaviors and a series of mareinitiated behaviors. The stallion reproductive sequence often 

Figure 9. A female feral horse is exhibiting elimination by urination. Urination behavior in horses is sexually dimorphic: female 

horses urinate in a posterior direction and male horses urinate in an anterior direction.
Ethogram 11

Figure 10. One of the most common harem social behaviors is allogrooming (also known as mutual grooming). It is expressed 

by the lateral parallel body position of two horses that allows for nibbling along the back or withers of each horse. While this 

behavior can be considered grooming, it is also thought to facilitate pair-bonding and dominance structure between band 

mates (Waring, 1983).

Figure 11. Olfactory investigation in the harem social behavior context is often observed as prolonged olfactory engagement 

of a female and her foal in a bonding regimen. This also may include licking and nudging.
12 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

Figure 12. Pair-bonding among juveniles within a band is also a common harem social behavior. In this example, female foals 

are closely engaging each other, which is thought to facilitate development of the female-female ethological relationships 

critical to band structure and stability later experienced as reproductive members of a family group (Crowell-Davis and 

others, 1986).

Figure 13. A feral horse stallion (leftmost horse) is herding females in his band by posturing and actively driving his females 

back into a cohesive group. Herding is the most common social behavior expressed by the dominant male toward females in 

his harem.
Ethogram 13

Figure 15. Male feral horses also express harem tending by maintaining fecal middens, or stud piles, in which feces are 

aggregated at strategically located positions within the band’s home range.

Figure 14. The blue roan stallion (foremost) is harem tending by expressing a posturing behavior and positioning himself 

between his harem females (several additional females out of the photo to the left) and an intruding male (right). Depending 

on the persistence and signals of the intruder, this behavior may develop into agonism.
14 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

(but not always) begins with herding or reproductive tending 

behavior. Reproductive tending is the close following of a 

female by the male, without the directional driving observed 

in herding behavior. Following this tending behavior, the 

stallion often vocalizes and exhibits the olfactory response 

known as flehmen (fig. 16) (Stahlbaum and Houpt, 1989). He 

then proceeds by rubbing his head on the female’s flanks and 

(or) resting his chin on her back, and extends his penis out of 

the prepuce (fig. 17). Some of these behaviors out of sequence 

are not necessarily associated with a stallion reproductive 

sequence; therefore, protocols to determine how to categorize 

the observed behavior are specified in figure 18. 

Female reproductive behavior is signified by estrous, 

which can sometimes be challenging to detect from typical 

field observation distances. A mare initiates her reproductive 

sequence by presenting herself facing away from the stallion, 

lifting her tail, and vocalizing (though sometimes the female 

faces the stallion first). These behaviors alone do not necessarily signify estrous, since the female could simply be vocalizing 

and preparing to defecate. If in estrous, it is typically accompanied by posturing her body with hind legs slightly apart (an 

apparent squat) and often turning her head toward her posterior. The mare also will frequently emit small streams of urine, 

a behaviour that is often concurrent with rhythmic ‘winking’ 

of her vulva: winking can be observed by the periodic flashes 

of pink from the inner coloration of her vaginal membranes 

(McDonnell, 2003). These contrasting pigments can be seen in 

the rolling female in figure 5, simply because of her posture. 

The urine emitted from female horses in estrous consists 

of specific variations of urinary volatile compounds that 

may facilitate chemical communication during reproductive 

behavior (Ma and Klemm, 1997). Female horses may express 

estrous behavior during the anovulatory period (typically 

winter) as well as during pregnancy (Crowell-Davis, 2007). 

Such anomalies to our conventional understanding may lead 

to misinterpretation of estrous behavior in the field and care 

should be taken to correctly and systematically identify this 

behavior.

Once both male and female are exhibiting reproductive 

behaviors, copulation may occur with the stallion mounting the female from behind, neck arched over her back and 

forelegs resting on her sides (fig. 19). Several events could 

occur in this situation and should be categorized separately if 

reproductive behavior is a focus of the research. These include 

successful copulation, unsuccessful copulation (the stallion 

cannot adequately mount the female for some reason), mare 

acceptance, mare rejection (the mare kicks and moves away 

from the stallion), and forced copulation (the mare is not presenting or accepting the stallion’s advance, but he relentlessly 

mounts her anyway).

Figure 16. Flehmen response in this feral horse stallion is displayed by the elevated head, and raised, inverted upper lip. 

This posture is a response to particularly exciting chemicals and olfactory signals that are detected by the main olfactory 

epithelium and concentrated directly into the vomeronasal organ, which in part controls sexual activity (Estes, 1972; Mills and 

Nankervis, 1999).
Ethogram 15

Figure 17. A feral horse stallion is exhibiting penis extension and rubbing of the female’s flanks as part of the male reproductive 

behavior sequence.

Figure 18. Basic guidelines for distinguishing reproductive and non-reproductive behaviors in stallions.

1. Tending/herding

2. Vocalization 

3. Flehmen 

4. Penis drop 

5. Rubbing flanks/chin rest 

6. Mounting 

If behavior 1 is not followed by 2–7 or 

confirmed as part of a reproductive 

sequence, then it is recorded as 

herding. 

Any of behaviors 2–3 that are not 

followed by 4–6 or confirmed as part of 

the reproductive sequence are 

recorded as harem social.

Penis drop not associated with an 

adjacent female is typically indicative 

of comfort behavior. 

Behaviors 5–6 are always associated 

with reproductive behavior. 
16 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

Parturition may also be included in the reproductive category or designated as its own behavioral category, depending 

on research focus. 

Agonism

Agonism in feral horses is exhibited by a wide range of 

behaviors and in this ethogram is put into seven categories 

arranged by increasing intensity of the interaction. Note that 

any or all of the following behaviors may be exhibited in play 

by young animals, in which case they should be considered 

comfort behavior rather than agonism. The first four categories 

of agonism may occur between males only, females only, or 

between males and females, but the remaining levels of agonism are typically observed only between males.

1. The most common and least intense form of agonism 

is the threat. Threats are characterized by laterally 

pinned back ears, arched neck, and (or) a movement 

of the head toward the opposing horse, but with no 

physical contact (fig. 20). Most conflicts and dominance interactions among feral horses are resolved 

by these gestures alone.

2. The next agonistic expression is the bump or push, 

which is expressed by the aggressor making forceful 

contact with another horse using its head, neck, or 

shoulder (fig. 21). 

3. As agonism escalates, the aggressor may chase its 

adversary at a gallop to displace the animal from the 

immediate area or with the intent of engaging the 

animal in more agonistic behavior (fig. 22). Chasing 

behavior is typically brief (seconds) or may last several minutes; however, the USGS study documented 

this behavior occasionally persisting over long time 

periods (greater than 1 hour) and great distances 

(greater than 3 km). 

4. The fourth level of agonism involves biting an 

opponent or kicking with the hind legs (fig. 23). This 

level involves physical contact, though serious injury 

is rare.

5. Rearing occurs when the horse lifts its forelegs off 

the ground and elevates its body into a more vertical position, thus looking larger to the opponent 

(fig. 24). While technically only a threat, this body 

position typically signifies a more intense agonistic interaction and provides the initial position for 

commencement of stomping, striking, boxing, and 

dancing behaviors. 

Figure 19. Successful copulation is occurring between this feral horse male and female. This reproductive behavior is 

characterized by a maintained mounting position on the female for the male and a relatively stationary, relaxed position for 

the female. Unsuccessful copulation is often a result of mare rejection, with the female expressing agonistic behaviors such 

as kicking toward the male and a brief mounting position for the male.
Ethogram 17

Figure 20. Agonism is expressed by both of these feral horses in the form of a threat. This is the most common form of agonism 

between feral horses and is most easily recognized by the laterally positioned, posterior pointing direction of the ears (shown 

in both animals here).

Figure 21. Pushing is an agonistic expression shown here by the foremost horse pushing toward the more distant horse.
18 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

Figure 22. Chasing is a moderately intense form of agonism and is shown here along with an expression of imminent biting 

behavior.

Figure 23. Biting is a common expression of agonism in equids and is expressed here between feral horse females to assert 

dominance.
Ethogram 19

Figure 24. Rearing is an expression often signifying a potentially intense agonistic interaction, typically between feral 

horse stallions.

Figure 25. Striking or stomping is being expressed by the feral horse stallion on the left. This behavior is typically indicative of 

highly agonistic expression and is expressed by the directed extension and downward motion of one or both front feet.
20 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

6. Stomping and striking occur when a horse uses one 

or both front feet to attack an opponent by extending 

the legs out and downward. This behavior has the 

potential to seriously injure the recipient (fig. 25). 

7. The most intense form of agonism between feral 

horse stallions is boxing and dancing. These behaviors involve the engagement of the agonists in 

vertical body positions and the use of the front legs 

in striking (boxing) or closer engagement that results 

in head and neck biting (dancing) (fig. 26). On 

very rare occasions, feral horse stallions have been 

observed engaging in prolonged fights resulting in 

considerable injury and sometimes fatal outcomes.

Submission

Submission is exhibited by the loser of the agonistic 

encounter. This may be expressed by simply running away, but 

also may be expressed with laid down ears (distally or posteriorly), lowered head posture, lowering of the hindquarters, and 

sometimes jaw snapping (especially in juveniles) (fig. 27).

Acknowledgments 

Thanks to Linda Coates-Markle, the late Dr. Francis 

J. Singer, and the many field technicians who voiced their 

opinions on how to aggregate these behaviors in the most 

meaningful way for its original research purpose. Many thanks 

to Hanem Abouelezz, Laura Caldwell, Melissa Esser, Marty 

Felix, Kayla Grams, Patti Grigsby, Susan Hahn, Billie Hutchings, Georgia Manus, Jane Nibler, Christina Petrandis, Phyllis 

Preator, Jennifer Severude, and Gerald Thygerson for the 

thorough notes and explanations in the margins of datasheets, 

which inevitably became as valuable for understanding equid 

behavior as did the rigidly collected and analyzed data points. 

J. Roelle, J. MacLeay, L. Zeigenfuss, and A. Kane provided 

useful and critical insights in their reviews of this manuscript. 

Thank you to S. McDonnell for expertise in helping us accurately define stallion reproductive behaviors. All photographs 

are courtesy of Jason I. Ransom. The National Park Service, 

U.S. Bureau of Land Management, and U.S. Department of 

Agriculture Animal and Plant Health Inspection Service provided administrative support and oversight during all USGS 

feral horse research efforts.

Figure 26. Boxing and dancing between these two stallions is illustrative of the highest level of agonism that feral horses 

typically express.
References 21

References

Aitchison, J., 1986, The statistical analysis of compositional 

data (with discussion): Journal of the Royal Statistical Society (B), v. 44, p. 1,313–1,325.

Aitchison, J., 1992, On criteria for measures of compositional 

difference: Mathematical Geology, v. 24, p. 365–379.

Altmann, J., 1974, Observational study of behavior—Sampling techniques: Behaviour, v. 49, p. 227–267.

Asa, C.S., Porton, I.J., and Calle, P.P., 2005, Choosing an 

appropriate contraceptive, in Asa, C.S., and Porton, I.J., 

eds., Wildlife contraception: Baltimore, Md., Johns Hokpins 

University Press, p. 83–95.

Bakeman, R., Forthman, D.L., and Perkins, L.A., 1992, Timebudget data—Log-linear and analysis of variance compared: 

Zoo Biology, v. 11, p. 271–284.

Beever, E.A., and Herrick, J.E., 2006, Effects of feral horses 

in Great Basin landscapes on soil and ants—Direct and 

indirect mechanisms: Journal of Arid Environments, v. 66, 

n. 1, p. 96–112.

Beever, E.A., Tausch, R.J., and Thogmartin W.E., 2008, Multiscale responses of vegetation to removal and horse grazing 

from Great Basin (USA) mountain ranges: Plant Ecology, 

v. 196, n. 2, p. 163–184.

Billheimer, D., Guttorp, P., and Fagan, W.F., 2001, Statistical 

interpretation of species composition: Journal of the American Statistical Association, v. 96, n. 456, p. 1,205–1,214.

Bingham, R.L., and Brennan, L.A., 2004, Comparison of type 

I error rates for statistical analyses of resource selection: 

Journal of Wildlife Biology, v. 68, n. 1, p. 206–212.

Buchholz, R., 2007, Behavioural biology—An effective and 

relevant conservation tool: Trends in Ecology and Evolution, v. 22, n. 8, p. 401–407.

Burnham, K.P., and Anderson, D.R., 2002, Model selection 

and multimodel inference—A practical-theoretic approach 

(2d ed.): New York, Springer Publishing, 488 p.

Clark, T.L., and Messina, F.J., 1998, Plant architecture and 

the foraging success of ladybird beetles attacking Russian 

wheat aphid: Entomology Experimental Applications, v. 86, 

p. 153–161.

Figure 27. Submission is being expressed by a young male horse (grullo [dark grey] horse in center) and directed toward the 

larger, dominant male (foremost), who is displaying threat behavior associated with dominance.
22 Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses

Coughenour, M., 2002, Ecosystem modeling in support of the 

conservation of wild equids—The example of the Pryor 

Mountain Wild Horse Range, in Moehlman, P.D., ed., 

Equids—Zebras, asses, and horses. Status survey and conservation action plan, IUCN/SSC Equid Specialist Group: 

Gland, Switzerland, and Cambridge, U.K., International 

Union for Conservation of Nature, p. 154–162.

Crowell-Davis, S.L., 2007, Sexual behavior of mares: Hormones and Behavior, v. 52, p. 12–17.

Crowell-Davis, S.L., Houpt, K.A., and Carini, C.M., 1986, 

Mutual grooming and nearest-neighbor relationships among 

foals of Equus caballus: Applied Animal Behaviour Science, v. 15, p. 113–123.

Dallaire, A., 1986, Rest behavior, in Crowell-Davis, S.L., and 

Houpt, K.A., eds., The veterinary clinics of North America, 

equine behavior: Philadelphia, W.B. Saunders Co., p. 

591–607.

Denniston, R.H., 1979, The varying role of the male in feral 

horses, in Symposium on the ecology and behavior of wild 

and feral equids, Laramie, Wyo., 6–8 September 1979, Proceedings: Laramie, Wyo., University of Wyoming, p. 93–98.

Doran, D., 1992, Comparison of instantaneous and locomotor 

bout sampling methods—A case study of adult male chimpanzee locomotor behavior and substrate use: American 

Journal of Physical Anthropology, v. 89, p. 85–99.

Eberhardt, L.L., Majorowicz, A.K., and Wilcox, J.A., 1982, 

Apparent rates of increase for two feral horse herds: Journal 

of Wildlife Management, v. 46, p. 367–374.

Elston, D.A., Illius, A.W., and Gordon, I.J., 1996, Assessment of preference among a range of options using log ratio 

analysis: Ecology, v. 77, n. 8, p. 2,538–2,548.

Estes, R.D., 1972, The role of the vomeronasal organ in mammalian reproduction: Mammalia, v. 36, p. 315–341.

Fahnestock, J.T., and Detling, J.K.,1999, The influence of herbivory on plant cover and species composition in the Pryor 

Mountain Wild Horse Range, USA: Plant Ecology, v. 144, 

p. 145–157.

Feist, J.D., and McCullough, D.R., 1976, Behavior patterns 

and communication in feral horses: Zeitschrift für Tierpsychologie, v. 41, n. 4, p. 337–371.

Garrott, R.A., Siniff, D.B., and Eberhardt, L.L., 1991, Growth 

rates of feral horse populations: Journal of Wildlife Management, v. 55, p. 641–648.

Garrott, R.A., and Taylor, L., 1990, Dynamics of a feral horse 

population in Montana: Journal of Wildlife Management, v. 

54, p. 603–612.

Gower, J., 2000, Horse color explained: North Pomfret, Vt., 

Trafalgar Square Publishing, 144 p.

Green, B.K., 2001, The color of horses—The scientific and 

authoritative identification of the color of the horse: Missoula, Mont., Montana Press Publishing, 127 p.

Heitor, F., Oom, M.M., and Vicente, L., 2006, Spatial relationships in a herd of Sorraia horses. Part I. Correlates of 

social dominance and contexts of aggression: Behavioural 

Processes, v. 73, p. 170–177.

Hobbs, N.T., and Hilborn, R., 2006, Alternatives to statistical 

hypothesis testing in ecology—A guide to self teaching: 

Ecological Applications, v. 16, n. 1, p. 5–19. 

Houpt, K.A., 1991, Investigating equine ingestive, maternal, 

and sexual behavior in the field and in the laboratory: Journal of Animal Science, v. 69, p. 4,161–4,166.

Houpt, K.A., and Keiper, R., 1982, The position of the stallion 

in the equine dominance hierarchy of feral and domestic 

ponies: Journal of Animal Science, v. 54, n. 5, p. 945–950.

Houpt, K.A., Law, K., and Martinisi, V., 1978, Dominance 

hierarchies in domestic horses: Applied Animal Ethology, v. 

4, p. 273–283.

Keiper, R., and Receveur, H., 1992, Social interactions of 

free-ranging Przewalski horses in semi-reserves in the 

Netherlands: Applied Animal Behaviour Science, v. 33, p. 

303–318.

Keiper, R.R., and Sambraus, H.H., 1986, The stability of 

equine dominance hierarchies and the effects of kinship, 

proximity and foaling status on hierarchy rank: Applied 

Animal Behaviour Science, v. 16, n. 2, p. 121–130.

Klimov, V.V., 1988, Spatial-ethological organization of the 

herd of Przewalski horses (Equus przewalskii) in AskaniaNova: Applied Animal Behaviour Science, v. 21, p. 99–115.

Klingel, H., 1975, Social organization and reproduction in 

equids: Journal of Reproduction and Fertility, Supplement 

23, p.7–11.

Levin, P.S., Ellis, J., Petrik, R., and Hay, M.E., 2002, Indirect 

effects of feral horses on estuarine communities: Conservation Biology, v. 16, n. 5, p. 1,364–1,371.

Ma, W., and Klemm, W.R., 1997, Variations in equine urinary 

volatile compounds during the oestrous cycle: Veterinary 

Research Communications, v. 21, p. 437–446.

McCort, W.D., 1984, Behavior of feral horses and ponies: 

Journal of Animal Science, v. 58, n. 2, p. 493–499.

McDonnell, S., 2003, A practical field guide to horse behavior—The equid ethogram: Lexington, Ky., The Blood 

Horse, Inc., 375 p.
References 23

Mielke, P.W., Jr., and Berry, K.J., 2007, Permutation 

methods—A distance function approach (2d ed.): New 

York, Springer Publishing, 439 p.

Miller, R., 1979, Band organization and stability in Red Desert 

feral horses in Symposium on the ecology and behavior 

of wild and feral equids, Laramie, Wyo., 6–8 September 

1979, Proceedings: Laramie, Wyo., University of Wyoming, 

p.113–128.

Mills, D., and Nankervis, K., 1999, Equine behaviour—Principles and practice: Malden, Mass., Blackwell Science, 232 p.

Mitlohner, F.M., Morrow-Tesch, J.L., Wilson, S.C., Dailey, 

J.W., and McGlone, J.J., 2001, Behavioral sampling techniques for feedlot cattle: Journal of Animal Sciences, v. 79, 

n. 5, p.1,189–1,193.

Molvar, E.M., and Bower, R.T., 1994, Costs and benefits of 

group living in a recently social ungulate— The Alaskan 

moose: Journal of Mammalogy, v. 75, n. 3, p. 621–630.

Nettles, V.F., 1997, Potential consequences and problems with 

wildlife contraceptives: Reproduction, Fertility, and Development, v. 9, p.137–143.

Porton, I.J., 2005, The ethics of wildlife contraception, in Asa, 

C.S., and Porton, I.J., eds., Wildlife contraception: Baltimore, Md., Johns Hopkins University Press, p. 3–16.

Pusey, A.E., and Packer, C., 1997, The ecology of relationships, in Krebs, J.R., and Davies, N.B., eds., Behavioral 

ecology—An evolutionary approach: Malden, Mass., Blackwell Publishing, p. 254–283.

Ransom, J.I., 2009, Understanding the influences of immunocontraception on equids through competing models of 

behavior: Fort Collins, Colo., Colorado State University, 

M.S. thesis, 61 p.

Ransom, J.I., Swann, M.E., Wilson, J.T., and Roelle, 

J.E., 2007, America’s wild horses and burros—

Research for management: Fort Collins, Colo., U.S. 

Geological Survey Fort Collins Science Center, 

http://www.fort.usgs.gov/wildhorsepopulations, accessed 

November 2008.

Rho, J.R., Srygley, R.B., and Choe, J.C., 2004, Behavioral 

ecology of the Jeju pony (Equus caballus)—Effects of 

maternal age, maternal dominance hierarchy and foal age on 

mare aggression: Ecological Research, v. 19, n. 1, p. 55–63.

Rubenstein, D.I., 1989, Life history and social organization in 

arid adapted ungulates: Journal of Arid Environments, v. 17, 

p.145–156.

Rubenstein, D.I, and Hack, M.A., 1992, Horse signals—The 

sounds and scents of fury: Evolutionary Ecology, v. 6, p. 

254–260.

Rutberg, A.T., and Keiper, R.R., 1993, Proximate causes of 

natal dispersal in feral ponies—Same sex differences: Animal Behaviour, v. 46, p. 969–975.

Smith, M.A., 1986, Impacts of feral horse grazing on rangelands—An overview: Journal of Equine Veterinary Science, 

v. 6, n. 5, p. 236–239.

Sponenberg, D.P., and Beaver, B.V., 1992, Horse color—A 

complete guide to horse coat colors: Ossining, N.Y., Breakthrough Publications, 124 p.

Stahlbaum, C.C., and Houpt, K.A.,1989, The role of flehmen 

response in the behavioural repertoire of the stallion: Physiology and Behavior, v. 45, p. 1,207–1,214.

Sutherland, W.J., 1998, The importance of behavioural studies in conservation biology: Animal Behaviour, v. 56, p. 

801–809.

Tilson, R.L., Sweeny, K.A., Binczik, G.A., and Reindl, N.J., 

1988, Buddies and bullies—Social structure of a bachelor 

group of Przewalski horses: Applied Animal Behaviour Science, v. 21, n. 1, p. 169–185.

van Dierendonck, M.C., Sigurjónsdóttir, H., Colenbrander, 

B., and Thorhallsdóttir, A.G., 2004, Differences in social 

behaviour between late pregnant, post-partum and barren 

mares in a herd of Icelandic horses: Applied Animal Behaviour Science, v. 89, p. 283–297.

Waring, G.H., 1983, Horse behavior: Park Ridge, N.J., Noyes 

Publications, 292 p.

Weeks, J.W., Crowell-Davis, S.L, Caudle, A.B., and Heusner, 

G.L., 2000, Aggression and social spacing in light horse 

(Equus caballus) mares and foals: Applied Animal Behaviour Science, v. 68, p. 319–337.

Wolfe, M.L., Ellis, L.C., MacMullen, R., 1989, Reproductive rates of feral horses and burros: Journal of Wildlife 

Management, v. 53, no. 4, p. 916–924. 

Publishing support provided by: 

Denver Publishing Service Center

For more information concerning this publication, contact:

Center Director, USGS Fort Collins Science Center

2150 Centre Ave., Bldg. C

Fort Collins, CO 80526-8118

(970)226-9398

Or visit the Fort Collins Science Center Web site at:

http://www.fort.usgs.gov/

— Ransom and Cade Quantifying Equid Behavior—A Research Ethogram for Free-Roaming Feral Horses—Techniques and Methods 2-A9