Graduate Thesis Or Dissertation
 

Morphological and endocrine correlates of dominance in male ring-necked pheasants (Phasianus colchicus)

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  • An investigation of the correlation between a number of behavioral, morphological and physiological parameters and dominance status of male Ring-necked Pheasants (Phasianus colchicus) was undertaken. Dominant males performed significantly more aggressive behaviors than subordinates and a higher proportion of these behaviors was directed toward distantly ranked subordinates. Animals could also be ranked in a subordinance hierarchy with subordinate males performing submissive behaviors and vocalizations at highest frequencies and directing the largest proportion of these behaviors toward distantly ranked dominants. A number of morphological characters were measured and their correlations with dominance status were investigated. Several significant correlations between certain body and wattle measurements were found. Experimental manipulations of the wattles were conducted to attempt to change behaviors and dominance status. Wattles of dominant birds were painted black to make them look subordinate. Wattles of subordinate birds were painted red to make them look dominant. Two of the dominant birds received more aggressive behaviors from true subordinates, after their wattles were painted. Two of the subordinate birds received fewer aggressive behaviors from true dominants, after their wattles were painted. Plasma levels of testicular hormones were measured during hierarchy establishment and in stable hierarchies. No correlations were found between testosterone levels and dominance status or frequencies of any of the agonistic behaviors measured. Exogenous hormones (estradiol, dihydrotestosterone, corticosterone, ACTH₄₋₁₀ and α-MSH) were injected to attempt to alter behaviors and change dominance status. These attempts were unsuccessful. My data conform to previously published reports on the use of morphological characters as signals of dominance status. My data also corroborate the absence of correlations of testicular hormone levels with dominance status and behavioral frequencies in other species of birds. The advantages of a status signalling system are discussed and reasons for living in a group and remaining subordinate are examined.
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