They are popular aquarium fish, although their aggressively territorial nature can pose problems if not closely watched.

Pebbled butterflyfish are monogamous and are aggressively territorial.

They are aggressively territorial, and at feeders or flowering shrubs they spend much time chasing other hummingbirds, rather than feeding.

Individuals are aggressively territorial from the age of about 3 months.

Convict cichlids are aggressively territorial during breeding and pairs are best kept alone.

Water voles are aggressively territorial, marking their patches with musk from flank glands.

A fiercely independent breed, Kintamanis can be aggressively territorial while at the same tender and affectionate with their own families.

Both sexes are aggressively territorial towards their own species when breeding and frequently pursue intruders into the air, attacking them in aerial "dogfights".

Formica rufa is aggressively territorial, and will often attack and remove other ant species from the area.

The Woodland Kingfisher is aggressively territorial, attacking intruders including humans.