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Hierarchy And Social Interactions In A Herd Psychology Essay

Factors related to dominance rank and the function of age, personality and weight were studied in two herds of horses. Subjects belonged to two distinctive groups: males and females. Male group consisted of 39 males 2-4 years old and a stallion 9 years old introduced into the group in a later stage of observations. Female group included 23 mares 1-21 years old and 7 foals (not included in part of the study). Dominance relationships among females were apparent and irrespective of rank difference. The dominance hierarchy was significantly linear and rank was positively correlated with age, personality, and weight (still to confirm need results!!!!!!!). NOT FINISHED YET

introduction

History And Background

As far in the past as 3000 BC, dogs, sheep and cattle were already domesticated. People also began to tame horses and first steps were taken where current Russia and North-East Asia are located nowadays. Although, first contact between human and horse was long before domestication the purpose was only to hunt and supply food. Nevertheless, with time people started to appreciate horses speed and hard work. This is when they began to use them for work. For these reasons people were forced to try to understand horses and learn more about their behaviour.

Time went by and people were becoming more civilised. With this progress they paid less attention to animals concentrating on different matters. They did not try to understand behaviour of animals. It happened, and it still does, that people who spent a lot of time with animals did not understand their basic needs; they did not want to and did not know how to read basic signals sent by them. Further, signals were wrongly interpreted if at all. Yet, the base of relationship between human and animal should be based on ability to communicate.

Excellent example of how well some people were able to use their knowledge to understand horses’ behaviour are Indians. Thanks to their approach to live, which was having respect to each living being, they were able to catch and break wild horse using simple, basic methods. Because Indians were capable of understanding horses, they used this knowledge to read their signals and needs. Hence, they could predict horses’ behaviour and respond to it.

It has been observed that people who are not educated but with high sense of sensibility are able to appreciate animals much better than people who are educated, whose attitude is typically physical. They do not understand animals and do not try or simply do not want to. Nevertheless, there are people who are interested in animal psychology. They make attempts to understand them. These people study behaviour of animals. They are able to notice differences in behaviour according to external factors.

Basics Of Behaviourism: Animals From Outside In

The first experimental design to test behaviour concentrated on introspection was performed by Wundt (1896). Since ‘consciousness’ trait was the only objective of the study, there was only one method possible where the subject and the researcher were the same person. Hence, there was no common object of research among researchers (Watanabe 2007).

After first attempts to investigate behavioural patterns another method was proposed by Watson (1913). He believed that introspection psychology was indirect research where animal psychology started to relay on similarities from human psychology. Later animal psychology became a basis for general psychology. Since scientists thought of animal behaviour as a simpler than human behaviour (Skinner 1938) they used it as basic data to analyze detailed data.

Yet another idea of early days of behaviourism was indicating that behaviourists believed that basic concepts such as reward, punishment, positive and negative reinforcements explained everything about animals, which were basically just stimulus- response mechanisms. According to Skinner (1971) all you needed to study was behaviour. There was no need to speculate what was inside a person’s or animal’s head because there was no measure to comprehend all the stuff inside the black box- intelligence, emotions, motives. The black box was off-limits. Only behaviour could be measure, hence, only behaviour could be studied (Skinner 1971).

For the behaviourists this was no great loss, since, according to them, environment was the only thing that mattered.

Some animal behaviourists took this idea to the extreme by teaching that animals did not even have emotions or intelligence. Animals only had behaviour which was shaped by mentioned above rewards, punishments, and positive and negative reinforcements from the environment. In this way, behaviourists did not focus what was inside black box. The brain is pretty powerful, and a person whose brain is not working right knows just how powerful. But back in the 1970s, when behaviourism was getting started to be discovered, people believed that everything was controlled by the environment.

Nowadays, term behaviour explains interactions between organism and its environment. It can be described as being conscious or subconscious, overt or covert, and voluntary or involuntary. In animals, behaviour depends on information received from the environment which then is maintained by the nervous and endocrine systems. The complexity of the behaviour of an organism is related to the complexity of its nervous system.

A critical analysis of the relationship between environmental input and behavioural output is required to understand the processes that mediate between them (Shettleworth 2000). Behavioural patterns may vary greatly. They may be very stable- no variations or very elastic- changes dependant on hormones, behaviour or learning. Behavioural studies are carried from physiological or behavioural point of view. Both ways of observations fulfil one another and both are essential in order to fully understand animals (Ville 1987).

Horses As Herd Animals: The Concept Of Dominance, Dominance Hierarchy And Social Structure

Horses are extremely social herd animals that favour living in a group. It is believed that group living could have progressed partly as a consequence of predation impact (Mendl and Held 2001). In fact, in prey species, which include most large vertebrates, fear of predators is considered to be a major factor in the formation and maintenance of groups (Sibbald et al. 2009). Members of a group usually are vigilant which reduces the cost to the individual (Pulliam 1973) and by being located close together it is harder for predators to hunt and kill members (Krakauer 1995). However, while fearfulness will generally motivate an animal to remain close to the group, the need to explore the environment in order to find food will motivate an animal to move away (Sibbald et al. 2009). The way how assorted group members establish this divergence will contribute to the structure of the group, since animals that are fearful will tend to remain close together and the ones that explore are likely to spend more time located at a distance from one another (Sibbald et al. 2009).

In the wild, new born foals must follow herd in order to survive. Mother’s company is all what the new born needs in the first few days of its live. With time, however, encouraged by social instincts foal begins to make acquaintance with other members of the group who shortly will become its family. A growing up foal tightens bonds with the herd while, at the same time, will be losing it with its mother (Jaworski 1998).

Like all living beings, equine social behaviour appeared in order to aid in a species survival. For instance, in the wild, if a horse was alone, there would be much greater possibility it could be eaten or attacked by a predator. Staying in a group means that animals have more of a chance to survive. Further, in a case of danger, there is a greater likelihood it would be noticed quicker by twenty horses than just one.

Dominance hierarchy can be observed in any herd. Horses will establish a pecking order, which is a hierarchical system of social organization in animals. It was first established by Schjelderup-Ebbe in 1921 to describe behaviour of poultry, hence, to establish dominance of birds. It has been developed for the purpose of maintaining which herd individual influences the behaviour of others, eats and drinks first, and so forth.

The concept of dominance has given insight into understanding of social structure in animals. Over the past three decades, however, widespread application of concepts and definitions of dominance have been introduced, leading to an ongoing debate about the usefulness and meaning of the concept (Drews 1993). Not only the wide application, but also the lack of establishing a definition of dominance that fulfils the requirements of a good definition, have caused difficulty in any systematic use of the concept (Smith). Disapprovals concerned on one description of dominance are not essentially relevant to other descriptions. Existing descriptions may be structural or functional, refer to roles or to agonistic behaviour, regard dominance as a property of individual or as an attribute of dyadic encounters, concentrate on aggression or on the lack of it, and be based either on theoretical constructs or on observable behaviour (Drews 1993).  NOT SURE WHETHER IT’S WORTH OF MENTIONING....

In general, what is agreed as dominance is the state of having high social status relative to other individuals, who react submissively to dominant individuals.

According to Drews (1993) dominance relations among two animals in a given group are specified as a consistent outcome of agonistic interactions. For instance, in study on a group of Japanese macaques (Macaca fuscata) one animal constantly dominated the other in 611 out of 630 dyads, one animal inconstantly dominated the other in 14 dyads and the incidents of 5 dyads finished with no conclusion (Takahata 1991). It is usual across agonistic interactions to become less frequent and harmful once dominance relations among individuals are established.

At a group level, it has been anticipated by some researchers that dominance relationships are to decrease aggression and maintain stability to the social group (Richards 1974; Kaufmann 1983). Aggression includes energetic costs, injury risks, and may reduce reproductive success in horses, by decreasing rates of conception and rising rates of fetal and foal mortality (Duncan 1982; Berger 1986; Linklater et al. 1999). It has been studied that new members within a group get involved in increased aggression during establishing dominance relationships among each other (Richards 1974; Linklater et al. 1999). Nonetheless, once these relationships are asserted, a dominant individual typically approaches or threatens a subordinate to obtain access to a resource (Houpt 1979). Hence, the decrease of aggression and the constancy of dominance relationship depend to a large extent on submissive and avoidance behaviours of subordinates (Kaufmann 1983).

Nonetheless, in particular conditions, benefits of dominance and hence aggression may outdo the cost. Models of evolutionary stable strategies (ESS) show that, when fighting for a resource, animal ought to bear in mind the value of the disputed resource, cost of injury and winning probability (Matsumura and Kobayashi 1998).

Dominance is influenced by diverse factors among species. In many species, it is thought that dominance is maintained by animal fighting capability (i.e. aggressiveness) or RHP (resource holding potential) (Maynard Smith and Parker 1976; Weeks et al. 2000). In a number of species, however, dominance between individuals is a consequence of their maternal rank (spotted hyenas, Crocuta crocuta, Frank 1986; horses, Equus ferus caballus, Weeks et al. 2000) or on the period length in the group as a consequence of subordination of recently united animals with group members (zebras, Equus zebra zebra, Rasa and Lloyd 1994; juncos, Junco hyemalis, Wiley 1990). Dominance rank in some species may depend on age, where older members usually are dominant over the younger members of the same sex (howler monkeys, Alouatta palliate, Jones 1980; horses, Equus ferus caballus, Rutberg and Greenberg 1990; Sigurjónsdóttir et al. 2003), height, weight (Rutberg and Greenberg 1990), physical state, social experience (Waring 1983) and duration of being in a group (van Dierendonck et al. 1995).

In a case dominance rank would stay stable, benefits related to high rank might raise a mare’s reproductive success (Côté 2000). High ranking females can be favoured as mating partners (Asa et al. 1979) and obtain advantages from low aggression towards them and their offspring (Rutberg and Greenberg 1990; Weeks et al. 2000). High-ranking females can also obtain benefits from better quality diets and bring up faster growing offspring which may raise earlier in some conditions (Duncan 1992).

Personality And Study Approach

Although scientists have been alert of the prospective meaning of animals' consistent individual variations in behaviour (Crawford 1938; Yerkes 1939; Itani 1959) as early as the beginning of XIX century, animal personality study is still a modern subject of research. It probably is inherited, especially in wild populations, and it shapes the individual’s behaviour as well as its fitness and life history.

As the new millennium arrived, it is most likely that researchers will direct their attention toward the genetic, biological, and environmental impacts on personality (Little 2001; Pervin and John 1999). They will probably look for genes that explain personality. They will try to clarify how the genes and environment interact to determine biological roots of personality (Gosling 2001). Investigators will also carry on research issues including how personality develops, how personality is linked to behaviour, social interactions and how personality treats are created in everyday life.

Nowadays personality is already a fast developing field of research. It includes both human and nonhuman-animals, which are already classified as one category regarding the above aspect. According to Pervin and John (1997) those characteristics that account for consistent patterns of feeling, thinking and behaving define personality and are known as cognitive. Since, there are limits to the application of this definition to animals, because the measurement of how animals think and feel is difficult, if not impossible, animals’ personality research has therefore focused on the assessment of observed behaviour in order to demonstrate individual differences (Lloyd 2008). This is where Mills’ (1998) theory seems to suit much better. He states that personality relies on the biological based behavioural tendencies of an individual. He believes that personality describes relatively stable, internal factors that cause an animal’s behaviour constant from one time to another. Further, this behaviour would vary from the behaviour that other individuals within the same species would demonstrate in the same or comparable situation (Child 1968). Additionally, consistent behaviours (habits) which are correlated together form traits (Zuckerman 1991) or, in other words, temperament (Thomas and Chess 1977; Schneider et al. 1991) where both terms describe the personality of an individual.

Yet another description is proposed by Kurvers and colleagues (2009) who describe animals’ personality as differences between individuals in behavioural and physiological traits being constant over time and context. Different behavioural and physiological responses enclose a genetic basis (van Oers et al. 2005) and are often correlated (Kurvers et al. 2009). It implies that these variations are essential features of the behavioural organization of individuals and are influenced by natural selection (Smith and Blumstein 2008) as well as sexual selection (van Oers et al. 2008).

Studies concentrating on identifying individual descriptive factors in nonhuman species are very broad. They start with research done on octopus (Mather and Anderson 1993), pig (Forkman et al. 1995) and finish on with gorilla (Gold and Maple 1994). Theoretically any sequence of measurements or tests can be employed to identify or make a distinction among individuals to establish individual uniqueness.

Current research done on horses’ personality have investigated individual differences via developing a variety of behaviour tests (Le Scolan et al. 1997; Wolff et al. 1997; Visser et al. 2001) and via applying rating system delivered by stable workers (Anderson et al. 1999; Momozawa et al. 2005).

In humans, the most popular method concentrates on producing questionnaires where the subject or the subject’s colleagues produce an evaluation for every trait being taken into consideration (Trembley et al. 1992). In several studies on animals, observer’s ratings were used to measure behavioural traits (Scolan et al. 1997). In some cases, this assessment depends on rating the level of animal’s reaction in a given situation (Budzynski et al. 1992) or on rating characteristics of behaviour in the natural environment (Stevenson-Hinde and Zunz 1978).

One of the best studied personality traits in a wide range of taxa is boldness (Kurvers et al. 2009). A number of research have illustrated that bolder characters occur more often in the leading edges of travelling groups (Harcourt et al. 2009; Kurvers at al. 2009; Shuett and Dall 2009). In foraging groups the pattern still remains the same (Kurvers et al. 2009).

Aim Of The Study

The purpose of this paper was to test whether dominance in a given herd of horses depends on individual’s personality, age and/or strength. There were two different groups of horses taken into consideration. The first one was consisted of 23 females (age between 1 year to 20 years old) with 7 foals. Second group contained 40 male horses (age between 2 to 10 years old). Results obtained from observation of those two groups were then compared and conclusions were made.

In the present study, individual behavioural traits of horses were rated by their owner. The aim was to see whether the established ratings for each individual were related to its position within the herd. The behavioural traits taken into consideration were as follow: affectionate, bold, intelligent, lazy, moody, sensitive and sharp.

It appeared that in both cases the dominant individual was the heaviest (based on a body weight), oldest and with the ‘bravest’ traits of its character (data provided by the breeder).

Dyadic interactions were performed to establish dominance hierarchy in a group of females. This was established using David’s score equations. Further, statistical analyses showed that there was a highly significant negative correlation between mean body mass and dominance rank (............................). Dominance rank position calculated from dyads interactions was also negatively correlated with age (..................................). Thus, the most dominant animals within herds tended to be the oldest and largest.

METHODOLOGY

Silesian Females

Subjects

30 Silesians female horses with 7 foals (Table 1), bred in Ryszard Szorc Stud and Stallion Stud in Książ, were used in the study. Animals were all in good health, had known each other very well and did not show any gregariousness. Before the experiment, they lived outdoors during summer and indoors during winter. They were individually identified with numbers written on either their necks or shoulders. During the experiment as well as after, animals were kept on the familiar to them paddock (Figure 1). They had an access to water and grazing at all times.

Test area

The test area was located at the field (Figure 2) in Plawna Gorna (Poland). The size was 5 hectares. Pasture was separated by a river. A bridge with a busy road crossed the field roughly in the middle. Shaded area for animals was provided by a forest as well as bushes. One part of paddock was flat whereas the other was hilly.

From one side paddock neighboured with an additional pasture. This field was also inhabited by a herd of horses. Both packs of horses interacted with each other from time to time. The opposite side of the field had an access to the road which was not particularly busy.

Observation and Data Collection

Behavioural observations were carried out on all 30 horses from 17 September 2009 to 23 September 2009. They were performed at different hours on each observation day. A 10- min acclimatisation period was allowed to pass before observations began, with the aim of reducing the observer effect (Martin and Bateson, 1993). Hence, horses could be observed from a 3 to 10m distance with no distraction. Behavioural data were recorded on prepared sheets and collected using scan sampling and continuous recording methods (Martin and Bateson, 1993) (Table 3). Animals were individually recognized by identification numbers on necks, variations in body size, morphology and coat colour. The structure and hierarchy of the whole herd was established. The study was constructed using 26 behaviourally defined adjectives. Ethograms (Table...) were developed combining behavioural definitions from published works (citation needed). Ethograms included measures of social behaviour, activity, and agonistic-related interactions including: aggression and subordination. Changes in behaviour patterns, weather condition and interaction between members of the social group were recorded every minute.

Experimental Test

The experiment took place at the pasture from 24 September 2009 to 27 September 2009. To stimulate the exercise horses were provided with a bucket of carrots, apples and/or oats.

Two horses were selected each time the experiment took place. The animals were not to be selected randomly as the stimulation had to be performed among all members of the herd (Table 2). Each dyad was lead away from the herd by a helper and once at appropriate distance (20 m) the horses were released and provided with a bucket of treats. The observer was at least 1 m away from tested animals.

Observations were made until the bucket was empty and the two tested horses returned freely to the group. In addition to behaviour patterns, duration of interaction between animals was recorded.

The number of interactions between dyads had not to be considerably different otherwise the Pij values (the amount of wins of individual i over individual j) would not be wholly appropriate for ranking group members (David 1988; de Vries 1998). In this case, each individual interacted with each member of the group. All foals were excluded from the study.

Calculation of dominance score

The binary matrix of dominance relationships was constructed. It involved dyads interactions which row individuals dominant over column individuals were assigned 1 and otherwise 0 (Heitor et al. 2006). In each dyad, an animal was considered to be dominant over the other if it forced other dyad individual to move back.

Individuals were assigned an ordinal rank increasing from the bottom to the top of the hierarchy.

Assigning the dominance scores for each horse was calculated using the David’s score model produced by Gammell et al. (2003). The calculations were based on win/loss asymmetries between dyad members.

The amount of wins by individual i in its interactions with another individual j (Pij) is the number of times that i defeats j (αij) divided by the total number of interactions between i and j (nij), i.e. Pij= αij/nij (Gammell, 2003). The proportion of losses by i in interactions with j, Pji=1–Pij. If nij=0 then Pij=0 and Pji=0 (David 1988; de Vries 1998). DS for each member, i, of a group is calculated with the formula:

where w represents the sum of i’s Pij values, w2 represents the summed w values (weighted by the appropriate Pij values) of those individuals with which i interacted, l represents the sum of i’s Pji values and l2 represents the summed l values (weighted by the appropriate Pji values) of those individuals with which i interacted (David 1988; de Vries 1998).

Statistical Analysis

The data did not follow a normal distribution and therefore non-parametric statistics were used. Correlations were tested using Spearman rank coefficient correlation test to indicate relationship between dominance score, age, weight and behavioural traits. Standard statistical tests were performed on Minitab 15.

Ratings of behavioural traits by the owner

The owner was asked to answer questions about his horses’ behavioural traits with an evaluation score from 1 (strongly disagree) to 5 (strongly agree) and 2 (agree), 3 (average), 4 (disagree).

He had to answer whether the horse was:

Affectionate

Bold

Intelligent

Lazy

Moody

Sensitive

Sharp

Data analysis

It is important to highlight that scored values have only a ranking value and do not correspond to absolute data.

Statistical analyses

The data for behavioural traits ratings did not follow a normal distribution and therefore non-parametric statistics were used. Correlations were tested using Spearman correlation test. Mann-Whitney matched pairs tests were performed for comparisons.

Silesian Males

Subjects

A total of 40 male horses kept at pasture at breeding industry in Pławna Dolna (Poland) where used in behavioural observations. All horses were privately owned and from a variety of backgrounds and breeding; some worked as carriage horses or were employed in riding lessons. Animals were in good health condition. All horses (except the stallion) were brought and introduced to the pasture as well as each other at the same time. At the beginning of behavioural observations animals did not know one another. Age ranged between 1 and 3 years with one exception- a dominant stallion (10 years old) that was introduced to the group in a later stage of the study. Breeds of all horses were known (.... Silesians, .........East-Friesians, .........Oldenburgs, ......Great-Poland horses). Animals were provided with free access to water and grazing.

In summer, horses were at pasture and in winter in stables. Housing conditions and handling methods while not at breeding industry were not known.

Observation area

Study was assessed on the pasture where animals were kept throughout the period of behavioural observations. The observation area consisted of a forest, a river, bushes and hills. The size of the observation field was approximately 25 hectares. Horses had a free access to water (river) at all time as well as grazing. The pasture included many paths and tracts to which human had a free access. There was a forest road in some places along the pasture. The road was not that busy since it was mainly used by farmers. Sheltered area was maintained by forest as well as bushes.

A pack of cattle had an open access to the field in a later stage of observations. It is not know whether all horses were familiarized with cattle before introducing at the pasture.

Observation

Behavioural observations took place from 02 September 2009 to 11 September 2009. Observations were based on developed ethogram constituting 15 behavioural definitions from published papers (citation needed). The ethogram contained social behaviour, activity, aggression and feeding aspects of behaviour. Behavioural observations were carried out on all 40 horses during the day only. Times of observations carried each day varied as well as the hours done per day. A 15- min familiarization period was maintained before observations to lower observer’s effect on animals. Behavioural data was gained using focal, and scan sampling and continuous recording methods. Focal as well as scan periods were 10 minutes long. An allocated break between each observation was 5- 10 minutes. Observation periods were short so as to reduce the effects of observer fatigue (Martin and Bateson, 1993). A total of 9 day observations were recorded.

Statistical analysis

Results

Discussion

In this study herd, the dominance hierarchy was significantly linear (Heitor et al. 2006). Rank was negatively correlated with age, however the oldest female was not at the highest position in the hierarchy. These observations are in agreement with research of others scientists (Rutberg and Greenberg, 1990; van Dierendonck ae al. 1995; Sigurjónsdóttir et al. 2003). Older mares may have greater fighting capabilities because of increased experience or have more to obtain in competitions over resources than younger mares (Heitor et al. 2006). The resources value associated with costs of aggression are expected to increase as females get older. It is due to an increase of fertility which occurs until 12-14 years of age (Matos 1996) and also a decrease of costs regarding potential reproductive success (Rutberg 1986). On the other hand, age may be a predictable condition that can be used to resolve conflict: individuals would learn to accept older group members in early stage of life, when variations in body size and social experience are greatest, and subsequently dominance relationships would be performed by animal recognition (Rutberg 1986). Further, age of females was related to length

According to Drent et al. (2003) differences in personality traits in males and females are usually independent of social status and sex.

Leadership thus dominance of one individual over another was best illustrated by the experimental test. Bolder and more intelligent individuals won interactions more often compared to less bold and less intelligent; they also won interactions more often and quicker.

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