[1] Mares is the recipient of the 2008 Jackson Award for exceptional service to the American Society of Mammalogists[2] and is most known for his works on convergent evolution, conservation, biogeography, systematics, and ecology of small mammals.

He is the co-editor of Latin American Mammalogy: History, Biodiversity, and Conservation[3] and the author of A Desert Calling: Life in a Forbidding Landscape.

In 1981, he joined the University of Oklahoma, where he held multiple appointments including serving as Professor of Zoology and Curator of Mammals at the Stovall Museum from 1983 to 2018.

[12] In collaboration with KA Ernest and others, he investigated small mammal community structure and composition in diverse habitats of Central Brazil,[13][14][15] yielding insights into various life-history characteristics.

[16][17] Furthermore, his research on Argentine mammals' ecology, distribution, and status analyzed demographic, historical, and socioeconomic factors influencing their populations, and provided a species list with occurrence details.

He has conducted field research in the United States, Mexico,Costa Rica, Venezuela, Colombia, Brazil, Argentina, Egypt, Iran, and India.

[31] Concentrating his research efforts on the unique adaptations and ecological characteristics of Tympanoctomys barrerae, his study shed light on its poorly known natural history and provided evidence for its convergence with other desert-dwelling rodents with similar dietary and physiological traits.