sentences:  Males also have a distinctive black "face mask", which curves into an elongated heart-shape surrounding a forehead of the principal brown colour.Unusually for a dimorphic ungulate, research has shown south Andean deer will congregate in mixed-sex groups, and the length of time spent inter-mixing increases with group size.The farther the animals are from rocky slopes the larger the size of observed groups, suggesting predation rates are lowest on slopes and greatest in open areas such as valley bottoms.