Characteristics of Dominant and Subordinate Led Social Groups of White-Tailed Deer in Illinois

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ABSTRACT.-

This study of dominant and subordinate led social groups of white-tailed deer (Odocoileus virginianus) was designed to investigate longevity and associations among members as well as the reproductive success that determines the durability of these groups. Characteristics of 25 dominant and 17 subordinate female led social groups of white-tailed deer were studied on three areas in Illinois. Group size for dominant led social groups ranged between 3.8 and 5.2 deer/y and for subordinate led groups only 2-2.5 deer. Dominant females survived significantly longer (8.2 y) then did subordinate females (5.4 y) and fawns born to dominants were significantly more sedentary after independence. Fawn recruitment (fawns alive at 1 y) was also significantly higher for fawns born to dominant females. Members of a dominant female's social group generally confined themselves to the home range of the dominant female but as they aged were seen less often with her. Dominant females occupied stable habitats free of environmental problems while subordinates occupied ranges with frequent natural and human induced disturbances. By association, fawns of dominant females inherit a stable home range that fosters improved longevity and successful fawn recruitment

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INTRODUCTION

How social groups form and maintain stability through time has not been well documented in the Midwest Agricultural Region. Permanent cover is scarce and fragmented in this Region, and female whitetails exhibit high levels of dispersal or migratory behaviors manifested in response to high spring population densities and limited parturition sites prior to agricultural crop maturation (Sparrowe and Springer, 1970; Vercauteren and Hygnstrom, 1994; Brinkman et al, 2005; Nixon et al, 2007, 2008). Social bonding among ruminants appears to have evolved as a means to better compete for resources and to aid in avoiding predation (Weckerly, 1999) . Family groups develop when the inclusive fitness of offspring that remain sedentary exceeds that of offspring that disperse from their natal range (Emlen, 1994).

White-tailed deer society is organized as groups of related deer that are led by a dominant matriarch surrounded by various relatives of both sexes that share portions of the matriarch's home range (Nixon et al, 1991; Porter et al, 1991; Miller and Ozoga, 1997). As dominance seems to be a function of age in white-tailed deer (Townsend and Bailey, 1981), the key to obtaining a dominant position is survival to an adequate age (Porter et al, 1991). Females must live long enough on a stable home range to produce offspring that perpetuate landscape tenure, with die matriarch and daughters able to fend off competing conspecifics.

Female fawns learn about their female relatives as early as the first month of life and this familiarity continues throughout life (Schwede et al, 1994; Tang-Martnez, 2001). Social inheritance of a home range among females evolves because selection should favor minimal dispersal of females, allowing grouping to reduce predation risk (Nelson and Mech, 1981). Proliferation of these social groups located on the most secure home ranges maintains the highest number of deer closest to the safest landscape (Nelson and Mech, 1981 ; Ozoga et al, 1982; Mathews and Porter, 1993; Mathews et al, 1997).

In this paper we were concerned with the effects of social rank on individual characteristics such as longevity and reproductive success, rather than how social rank was obtained at the time of capture (through dyad encounters won and lost) . Dominant and subordinate rank refers to the female social position in the population as a whole based on years of deer observations on the study areas, often from shortly after birth until death. We compare the frequency of association, survival, fawn recruitment and dispersal rates for known dominant and subordinate females and their offspring on three study areas in Illinois where female dispersal is a prominent characteristic of population dynamics. …