Everyone knows the bird on the English Christmas card. European robins may look cute but they are not very tolerant. They can be very aggresive when defending their large territory. They will stick out their chests, shake their body back and forth and eventually assault their competitor with their beaks. They mark off their territory by singing. Their pearly song can be heard throughout the year: a kind of tinkling waterfall of whistled tones. It's not just the males that mark the territory while singing, the females sing just as loudly.