Bovid Horns: An Important Site for Heat Loss during Winter?

Bovid horns play a prominent role in social and sexual interactions. In cold climates, however, heat loss through the horn surface may represent a major energy cost. We measured surface temperatures of horns ( T h) for two Barbary sheep (Ammotragus lervia; one male and one female) at the Granby Zoo, Québec, using temperature-sensitive radiotransmitters. Over ambient temperatures ( T a) of 5 to -19°C, T h never dropped below 3°C. At T a≈ -10⚬ C, the difference between T hand T a was 17°C for the male and 21°C for the female. Using empirical models to predict heat loss through horns and resting metabolic rates, we estimate that, at T aof≈ -10⚬ C, heat loss through the horn surface is 20% of resting metabolic rate for females and 29% for males which have larger horns than females. We argue that the metabolic costs of possessing large horns in cold climates may impose constraints on morphology and sexual selection.