When flocking is costly: reduced cluster-flock density over long-duration flight in pigeons

Area of Science:

• Animal behavior
• Bioenergetics
• Aerodynamics

Background:

• Birds in cluster-flocks gain predator deterrence through group patterns.
• Cluster-flocking incurs higher energetic costs than V-formations, especially in dense groups.
• This highlights a trade-off between energy expenditure and flocking benefits.

Purpose of the Study:

• To investigate how flight duration affects energetic costs and flock structure in homing pigeons.
• To examine the trade-offs between increased work rate and flocking benefits over time.

Main Methods:

• Six homing pigeons (Columba livia) were equipped with GPS and accelerometer biologgers.
• Pigeons undertook a 177 km, 256-minute flight, deviating from a standard training route.
• Analysis focused on changes in pairwise/group distances and flap frequency over the flight duration.

Main Results:

• Pigeons' pairwise and group-level distances increased significantly during the long-duration flight.
• Flap frequency of individual pigeons decreased over time as the flight progressed.
• Changes in flock structure and flight mechanics were observed as birds fatigued.

Conclusions:

• Over long flights, the energetic costs of close proximity in cluster-flocks become prohibitive.
• The anti-predator benefits of tight cluster-flocking are likely diminished as fatigue sets in.
• Proximate costs of flying with conspecifics can override ultimate flocking functions during extended flights.