Sarah Medill – Ph.D.

Sarah 2014 (small)
Sarah Medill joined the Sable Island study and the University of Saskatchewan as a PhD Student in January 2012. Her research is focused on social structure of feral horses and the interactions between sociality and population dynamics (i.e., sex ratio and density affects). Not unlike some primates, feral horses live in small groups which perform best when maintaining constant membership. Band size may remain relatively stable despite fluctuating population dynamics but Sarah will investigate whether in fact band membership remains constant by the individuals present and how population level changes can influence group dynamics of immigration, emigration, birth, and death.

In addition to investigating the interplay between population and group level dynamics, Sarah is investigating hair cortisol concentrations from sampled mane and tail hair. Cortisol, a hormone associated with the activation of the Hypothalamic-Pituitary-Adrenal axis, is increased during periods of stress in order to mobilize energy stores. Cortisol is assimilated into the hair shaft during its growth and provides a record of the relative concentration of the free cortisol circulating during the concurrent time. To better understand the importance of sociality, cortisol will be compared to an individual’s social entropy (how frequently they change associations), group dynamics, and dominance hierarchies. She will also be able to use hair cortisol to investigate the cort-fitness and cort-adaptive hypothesis; two opposing explanations for why high cortisol may be observed under different situations. And lastly, offspring of different sex may increase their physiological cost to mothers which may be reflected by hair cortisol which could provide additional support for the Trivers-Willard Hypothesis in this species.

Additional Background:

After graduating from University of Manitoba with B.Sc. (Hons.) Ecology in 2004, Sarah took on a technician position with a student of University of Nevada – Reno working with the feral horses in Nevada. Instantly fascinated by their social system she had little success finding a supervisor in Canada interested in starting a research project with any of Canada’s feral horse populations. Advised to get a Masters in another area she looked to another field of personal interest which was Human-Bear conflict and was elated to find a position working with Dr. Andrew Derocher on polar bears. After completing her M.Sc. at the University of Alberta (2008), she immediately took a position with the Government of Nunavut’s Department of Environment as the Wildlife Deterrent Specialist and remained there until 2011. When the opportunity to return to research on feral horses arose she eagerly joined the McLoughlin lab, but not before completing a term position with Parks Canada in Jasper, AB as a Resource Manager & Public Safety Specialist.


Richard, E.S.E. SimpsonS.A. Medill, and P.D. McLoughlin. 2014. Interacting effects of age, density, and weather on survival and current reproduction for a large mammal. Ecology and Evolution (accepted August 5, 2014).

Medill, S., Renard A., and Larivière S. 2011. Ontogeny of antipredator behaviour in striped skunks (Mephitis mephitis). Ethology, Ecology, & Evolution 23: 41-48.

Medill, S., Derocher, A.E., Stirling, I., and Lunn, N. 2010 Reproduction recorded in the cementum of female polar bears (Ursus maritimus). Polar Biology 33(1): 115-124.

Medill, S., A.E. Derocher, I. Stirling, N. Lunn, and R.A. Moses. 2009. Reducing variation and error when estimating cementum deposition from longitudinal sections of polar bear (Ursus maritimus) teeth. Journal of Mammalogy 90(5): 1256-1264.

Renard, S. Medill, and S. Larivière. 2009. Ontogeny of sexual size dimporphism in striped skunks (Mephitis mephitis). Acta Theriologica 54(3): 243-248.

Larivière, S., Y. T. Hwang, W. A. Gorsuch, and S. A. Medill. 2005. Husbandry, overwinter care and reproduction of captive striped skunks (Mephitis mephtitis). Zoo Biology 24: 83-91.