To see if there were any common links among dogs who had bitten a child within a particular four-year period, researchers examined 111 cases of dog bites by 103 dogs, all referred to the same veterinary behavior clinic in Philadelphia.
They found several distinctive behavior patterns that related to the dogs' territorial behaviors, and suggested the main causes of aggression in dogs across different breeds.
Analysis showed that young children (under 6 years) were more likely to be bitten when a dog felt the kids were threatening to take its food or toys.
Older children were bitten when the dog felt the kids were encroaching on its territory. Children with whom the dog was familiar were more likely to be bitten in relation to food guarding, while unfamiliar children were more likely to be bitten in relation to territory guarding.
Behavioural analysis revealed that, the guarding of resources and territory were the most common causes of aggression among the dogs.
Three quarters of the biter dogs studied exhibited anxiety, either by being left by their owners or being exposed to some loud noise, such as a thunderstorm or fireworks.
Young children in particular tend to be noisy and make unpredictable movements, which could frighten an already anxious dog and cause them to bite the child, the researchers said.
Half of the dogs also had medical conditions, such as eye problems, liver and kidney disease, and diseases that affected their bones and skin.
Study authors suggest that pain from these conditions could have pushed the dogs over the edge, causing them to bite.
The findings are published in the recent issue of journal Injury Prevention.