What visual cues can trigger territorial aggression in robins?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

red deer stags (Cervus elaphus) — Aggressive behaviour A pair of red deer stags (*Cervus elaphus*) competing for possession of a female in the rutting season.

In the context of aggressive behaviour, territorial robins are triggered to attack by specific visual cues. A well-documented example is their tendency to vigorously attack a bunch of red feathers placed within their territory, which serves as a visual stimulus for defensive aggression.1

It is important to note that such aggression is not an inflexible, automatic response. Whether a robin chooses to attack a perceived rival depends on its internal state, including the activity of its nervous system and the levels of hormones circulating in its blood. Consequently, the same visual cue may elicit an attack on one occasion but be ignored on another.1