Most theories predict more aggression higher up the ladder, but researchers say the difficulty of working out the pecking order in the crowded middle leads to aggression.

Top dogs in a pack are known to assert their dominance, but scientists who studied a group of free-roaming mongrels have found high levels of aggression in the middle of the dominance hierarchy.

Most theories predict more aggression higher up the ladder. However, researchers said the difficulty of working out the pecking order in the crowded middle leads to aggression.

Dominance hierarchy

The research was carried out by the University of Exeter and the Azienda Sanitaria Locale (ASL) – Roma 3 Servizio Veterinario, Italy. Matthew Silk, of the university’s Environment and Sustainability Institute, said: “Our results reveal the unavoidable costs of climbing a dominance hierarchy.”

Science Daily reported: “In the middle of the hierarchy – where it’s harder to predict which animal should be dominant – we see lots of aggression.”

Rome suburbs

The year-long study examined a pack of 27 mongrel dogs that roamed freely in the suburbs of Rome. The dogs did not live with humans, although relied on them for food.

Eugenia Natoli, from the ASL – Roma 3 Servizio Veterinario, said: ”Our results confirm these dogs have an age-graded dominance hierarchy similar to that of wolves.”