Irritable male syndrome (IMS) is an annual behavior pattern that has been described in Soay sheep and other mammals with a strictly seasonal breeding pattern and described in a 2002 literature review of animal behavior by Lincoln A. Gerald. IMS is a striking feature in mammals with seasonal breeding patterns; it manifests at the end of the mating season. The term covers symptoms thought to be caused by a drop in testosterone levels in male mammals. Similar behaviors have been observed in red deer, reindeer, and Indian elephants.