The bottlenose dolphin can behave aggressively. Males fight for rank and access to females. During mating season, males compete vigorously with each other through displays of toughness and size, with a series of acts, such as head-butting. They display aggression towards sharks and smaller dolphin species. At least one population, off Scotland, has practiced infanticide, and also has attacked and killed harbour porpoises. University of Aberdeen researchers say the dolphins do not eat their victims, but are simply competing for food. However, Dr. Read of Duke University, a porpoise expert researching similar cases of porpoise killings that had occurred in Virginia in 1996 and 1997, holds a different view. He states dolphins and porpoises feed on different types of fish, thus food competition is an unlikely cause of the killings. Similar behaviour has been observed in Ireland. In the first half of July 2014, four attacks with three porpoise fatalities were observed and caught on video by the Cardigan Bay Marine Wildlife Centre in the Cardigan Bay, Wales.