University of Central Florida Undergraduate Research Journal - Social Behavior in a Herd of Captive Male Giraffes
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Social Behavior in a Herd of Captive Male Giraffes

By: Patrick Ziarnowski and Kaidi Fenrich | Mentor: Frank Logiudice

Discussion

In the wild, adult male giraffes rarely associate with the same individual on multiple occasions (Dagg and Foster, 1976). Thus the conditions of a zoo habitat may allow for types of social encounters in all-male groups to be studied where all individuals are in the same herd for months or even years. With resources such as food and water clustered in specific locations and with giraffes in forced proximity to one another, it is possible to document a multitude of agonistic behaviors in the zoological environment (Horová et al., 2015)

In giraffes, agonistic behavior, consisting of behaviors relating to conflict and dominance, includes aggressive behavior such as hitting and necking, as well as behaviors that may not include any physical contact but that serve as indicators of dominance or of submission, including dominance gestures, submissive gestures, threat displays, displacement, and yielding. The principal benefit derived from dominance is access to limited resources (Goodenough et al., 2010). Members of the same social group exist in the same geographic area and have physical access to the same resources, such as food, water, mates, and territory. The primarily disputed resource in giraffes is female mates, though in captive giraffes, agonistic behavior may be seen in regards to clustered resources such as food and water. The submissive individual yields to the dominant individual over these resources.

The establishment of a dominance hierarchy determines in advance an individual’s level of access to a resource, allowing overt conflict to be minimized. In captive giraffes, the dominance hierarchy is linear (Horová et al., 2015). Asymmetries in size, strength, and experience favor one individual winning in a fight against another, and these factors impact oneás position within the dominance hierarchy (Goodenough et al., 2010). Larger size, greater strength, and increased experience in fighting enable an individual to win conflicts and may lead to harm or death in the other individual. Through the expression of dominance gestures by the dominant individual, the submissive individual may evaluate asymmetries in size and strength. These asymmetries can serve as predictors of the outcome of a conflict, and may determine whether the risk of losing a fight outweighs the benefits gained by the contested resource. As a result, the submissive individual must either challege the dominance gesture through a threat display or accept the other individual's dominance, often by expressing a submissive gesture. Agonistic behavior that is not inclusive of aggressive behavior allows for the outcome of a fight to be agreed upon in advance, with the dominant individual gaining access to resources without physical harm occurring to either individual.

Sparring occurs frequently in subadult male giraffes but occurs rarely in mature bulls (Pratt and Anderson, 1982). Early explanations of the behavior have included establishing a dominance hierarchy and fostering social cohesion (Coe, 1967). However, a later study found little evidence to support a relationship between sparring and dominance; instead the study posited it to be a form of play, providing benefit to the giraffe later in life as it allows him to practice his fighting skills in a harmless manner (Pratt and Anderson, 1985).

Play incorporates fragments of other behavior in complete or incomplete sequence, serves no immediate purpose, and is often of exaggerated form (Goodenough et al., 2010). It typically resembles crucial behavior seen in adults, serving the purpose of discovering the best combination of actions and reinforcing them so that they can be firmly established and competently performed as an adult (Wilson, 1980). For example, a giraffe that has had sufficient experience in sparring may be more likely to later succeed in necking matches against other bulls, and in turn is more likely to gain access to estrous females and increasing reproductive success.

Seeber, et al. (2012) noted that the widely accepted function of investigating behavior is to stimulate the female giraffe to urinate. Dagg (1958) stated that in her observations in the wild, she observed males exclusively urine test females. However, flehmen responses have been observed in captive environments between males in mixed-sex exhibits, although at lower frequency than between bulls and cows (Meredith J. Bashaw, personal communication, February 2016). Additionally investigating behavior has been observed being directed toward either sex, by bulls as well as by cows (Seeber et al., 2012). Male-male mounting among younger giraffes has been well-documented in wild giraffes (Dagg and Foster, 1976; Innis, 1958; Pratt and Anderson, 1985; Seeber et al., 2012).

Among the most compelling explanation for male–male mounting is that it is a harmless by-product of other adaptations, namely high sexual motivation It may potentially serve in social functions such as fostering social bonds, displaying dominance, and practice for copulation (Sommer and Vasey, 2006). A study on malemale mounting in American bison (Bison bison) found no correlation with social rank and contended that it may play a role in social bonding, and in acquiring experience, although crucial steps including penetration were missing (Vervaecke and Roden, 2006).

In this study, we did not find any association between mounting and dominance: Emba and Rafiki mounted each other at similar frequencies, in spite of a difference in rank. Meanwhile, no mountings occurred between Gage and Emba, even though the same rank relationship exists between Gage–Emba as it does for Rafiki–Emba. There may be evidence of reciprocity, as dyad mounting frequencies were comparable, suggesting mounting plays a social role: Rafiki mounted Emba at a similar frequency to the inverse relationship, while no mountings occurred between Gage and Emba, and mountings between Gage and Rafiki occurred at low but comparable frequencies. However, co-browsing and co-feeding occurred only between Rafiki and Gage, which was complemented by relative mounting frequencies. This pattern may suggest that co-browsing and male-male mounting serve different social functions. While co-browsing is found among giraffes of equivalent dominance ranking, mounting may serve as a means for challenging one’s position in the dominance hierarchy. Rafiki’s mountings of Emba may represent him testing his place in the hierarchy.

Conclusion>>