Fine-scale foraging behaviour of a medium-ranging marine predator

Area of Science:

• Marine ecology
• Animal behavior
• Oceanography

Background:

• Predator movement patterns are crucial for detecting prey patches at various scales.
• Area-restricted search (ARS) behavior is a key strategy for efficient foraging.
• Understanding foraging strategies in seabirds like northern gannets is vital for marine ecosystem studies.

Purpose of the Study:

• To investigate the foraging strategy of northern gannets in the western North Sea.
• To test for hierarchical ARS behavior and its relationship with oceanography and prey detection.
• To determine if ARS behavior is linked to increased foraging effort and success.

Main Methods:

• Utilized fine-scale movement and activity data from northern gannets.
• Applied first-passage time (FPT) analysis to identify ARS zones.
• Correlated ARS zone locations with physical oceanographic features like tidal mixing fronts.

Main Results:

• Northern gannets displayed hierarchical ARS behavior on most foraging trips, with nested scales observed.
• ARS zones were frequently located near tidal mixing fronts, indicating oceanographic influence.
• ARS initiation was typically followed by diving, suggesting prey detection as a trigger, though not all prey encounters induced ARS.
• Dive rates were significantly higher within ARS zones, especially nested ones, correlating with foraging effort.

Conclusions:

• Northern gannets employ a hierarchical foraging strategy involving nested ARS behavior.
• Physical oceanography, particularly tidal mixing fronts, influences the location of ARS zones.
• Prey detection triggers ARS, which in turn enhances foraging effort and likely success by matching prey distribution.