Document Type

Thesis

Date of Degree Completion

Winter 2018

Degree Name

Master of Science (MS)

Department

Primate Behavior

Committee Chair

Dr. Lori K. Sheeran

Second Committee Member

Dr. Susan Lonborg

Third Committee Member

Dr. Jessica A. Mayhew

Abstract

ABSTRACT

GORILLA LIFE-STAGE COMPARISON OF HEAD ORIENTATION

by

Lisa Kay Wilding

January 2018

Staring by primates, as well as other species of animals, can be perceived as a threat and averting that gaze can minimize potential conflict. Given that gorillas are highly sexually dimorphic, they may use this staring and gaze aversion strategy more than physical contact. Due to the shape of the eye and the pigmented sclera in some primates, eye gaze can be difficult to determine, whereas, head orientation may be a more salient cue. The current study documents developmental differences among age-sex classes of captive western lowland gorillas (Gorilla gorilla gorilla) in six head orientation categories (Head Toward Other, Head Toward Other Aversion, Continuous Head Orientation >= 2 secs, Continuous Head Orientation >= 3 secs, Mutual Head Toward Other, and Head Not Toward Other) toward conspecifics. Individuals were grouped into eight age-sex classes: infant females, infant males, juvenile females, juvenile males, subadult females, subadult males, adult females, and silverback males. In Head Toward Other, juvenile males oriented toward others significantly more than the expected frequency compared to other age-sex classes, whereas subadult females oriented toward others significantly less. In Continuous Head Orientation >= 2 secs, infant males and silverbacks oriented toward others significantly more than the expected frequency compared to other age-sex classes; whereas juvenile males oriented toward others significantly less. In Continuous Head Orientation >= 3 secs, juvenile males oriented toward others significantly more than the expected frequency compared to other age-sex classes. These findings indicate that staring, as denoted by head orientation, is not inversely proportional to age, but tends to be related to sex and maturity of the individual. No significant differences between observed frequencies and expected frequencies of the population were detected in Head Toward Other Aversion, Mutual Head Toward Other, and Head Not Toward Other.

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