How do herring gulls establish and defend breeding territories?

Herring gulls (Larus argentatus) establish and defend breeding territories—typically 30 to 50 metres in diameter—by utilizing a repertoire of aggressive displays designed to intimidate intruders.1

When a bird encounters an intruder on its territory, it may employ several specific postures:

• Oblique with long call: The bird stretches its neck obliquely forward and upward, holds its wings slightly away from its body, and emits a loud, long-drawn call with its bill wide open.1
• Upright threat posture: The bird raises its head, angles its bill downward, and holds its wings stiffly apart. This may escalate into a charge, where the bird runs or half-flies toward the intruder.1
• Choking: Both members of a pair may stand with legs bent, breasts lowered, and heads pointed down, rhythmically jerking their heads while uttering a deep call.1
• Pecking the ground: The bird aggressively pecks at and tears out vegetation, such as moss or grass, often tossing it aside.1

While these displays are usually effective at maintaining boundaries, they can occasionally escalate into physical fights involving pecking and wing-pummeling. Once territories are established, neighboring gulls generally recognize and tolerate one another, causing aggressive behavior to subside.1