How Nature Works: Gull Territoriality

Summary

On Appledore Island, Greater black-backed and herring gulls coexist through a sophisticated system of social signals that minimize violence. These predators, which eat anything they can catch, have developed territorial behaviors to protect their nests and young. They use various calls and visual displays to communicate and maintain boundaries, reducing conflict despite the risk of fights. This signaling system has evolved to favor communication over conflict, ensuring the survival of eggs and chicks.

Takeaways

• 🌍 Greater black-backed and herring gulls breed on Appledore Island off the New England coast, completing their life cycle in just three months.
• 🦅 These gulls are both predators, consuming a wide range of prey, including other gulls' eggs and chicks.
• 🤔 Despite being potential predators to one another, thousands of gulls coexist on a small 95-acre island.
• 📢 The gulls have evolved a complex system of social signals to minimize violence and maintain order within the colony.
• 🏠 Males arrive first in spring, followed by their mates, returning to the same territory they held in previous years.
• 🚶‍♂️ The experienced pairs inspect their territory, reinforcing boundaries to protect their nesting sites.
• ⚠️ Territorial boundaries must be constantly defended using various signals, including the long call, mew, Kek Kek, and Yeow.
• 🦢 The gulls use visual displays like the Upright Posture and the charged display to threaten or deter intruders.
• 🤼‍♂️ While fights do occur, they are risky because injury to a parent could doom their offspring.
• 🕊️ Over time, natural selection has favored communication over conflict, resulting in a signaling system that reduces violence within the breeding colony.

Q & A

What are the two species of gulls mentioned in the script that breed on Appledore Island?

The two species of gulls mentioned are the Greater black-backed gull and the herring gull.

How long does the breeding season last for these gulls on Appledore Island?

The breeding season for these gulls lasts for three short months.

What kind of behavior do the gulls exhibit towards each other on the island, considering they are predators?

The gulls exhibit territorial behavior and use various social signals to minimize violence and conflict among themselves.

How do the gulls establish and maintain their territories on the island?

Gulls establish and maintain their territories by using social signals and displays to mark and defend their spaces, which are spaced 4 to 5 meters apart.

What is the significance of the long call in the context of the gulls' territorial behavior?

The long call is a threat directed at trespassers, used by the gulls to assert their territorial boundaries.

What role does the mew call play in the gulls' social interactions?

The mew call is used in territorial disputes, often to call for support from a mate.

When is the Kek Kek call used by the gulls?

The Kek Kek call is used when the colony is disturbed or during boundary disputes.

What is the purpose of the Yeow call in the gulls' communication?

The Yeow call serves two functions: it is used in boundary disputes and when the colony is disturbed.

Can you describe the Upright Posture displayed by the gulls?

The Upright Posture is a visual display where the gull's neck is stretched up and forward, head slightly down, and wings are cocked forward and slightly off the sides, indicating a readiness to attack.

What is the charged display and how does it differ from the Upright Posture?

The charged display is a more aggressive ritualized attack amplified by outstretched wings, making the gull appear larger, as opposed to the Upright Posture which is a more rigid stance.

Why are fights risky for the gulls despite their signaling system?

Fights are risky because severe injury to a parent gull can result in the failure to protect and care for their eggs and chicks, which would be detrimental to their offspring's survival.

How has the signaling system evolved to reduce violence among the gulls?

Over evolutionary time, selective pressure has favored communication over conflict, leading to a signaling system that minimizes violence in the breeding colony.