Foraging for high caloric anthropogenic prey is energetically costly

Area of Science:

• Ecology
• Animal Behavior
• Bioenergetics

Background:

• Generalist species often benefit from human-provided food resources.
• Anthropogenic food sources are typically high in calories but may require specialized foraging skills.
• Not all individuals equally exploit these resources, with some preferring lower-energy natural habitats.

Purpose of the Study:

• To investigate the energetic costs of foraging in human-influenced habitats versus natural habitats for herring gulls (Larus argentatus).
• To determine if increased flight costs contribute to higher energy expenditure in areas with anthropogenic food sources.

Main Methods:

• Utilized GPS trackers with tri-axial acceleration measurements on herring gulls.
• Quantified time-energy budgets to assess energy expenditure during foraging trips in different habitats.
• Compared energy expenditure between foraging in marine/urban areas and intertidal/agricultural areas.

Main Results:

• Energy expenditure was 34% higher on average when foraging on high-calorie anthropogenic prey compared to low-calorie natural prey.
• Birds would need to gather approximately 400 kJ more daily to compensate for increased foraging costs in human-influenced areas.
• Significant differences in energy expenditure were observed between foraging habitats.

Conclusions:

• Foraging habitat significantly influences energy expenditure in herring gulls, impacting their foraging decisions.
• Changes in the management of anthropogenic resources may alter the costs and benefits of associated foraging strategies.
• Individual foraging decisions are likely a balance between energy expenditure and resource availability.