Optimal foraging and beyond: how starlings cope with changes in food availability

Area of Science:

• Animal behavior
• Physiology
• Ecology

Background:

• Optimal foraging models traditionally focus on behavioral decisions, often treating physiological responses as fixed constraints.
• Understanding foraging adaptations requires integrating behavioral, physiological, and energetic factors.

Purpose of the Study:

• To investigate behavioral and physiological responses of European starlings (Sturnus vulgaris) to varying food availability and work requirements.
• To test the applicability of different currencies (efficiency vs. net rate) in explaining foraging choices.

Main Methods:

• Laboratory experiment with European starlings in a closed economy.
• Two foraging modes (flying, walking) and two work treatments (hard, easy) were manipulated.
• Behavioral (time budgets, mode preference) and physiological (metabolism, body mass, fecal energy) data were collected.

Main Results:

• Higher work load in the hard treatment led to lower daily intake but also lower total daily expenditure due to reduced overnight metabolism.
• Birds exhibited greater food utilization (lower fecal caloric density) in the hard treatment.
• Foraging choices aligned with maximizing net energy gain per unit time, not energetic efficiency, and were not explained by time constraints.

Conclusions:

• European starlings exhibit complex foraging adaptations involving integrated behavioral and physiological adjustments.
• Simple optimal foraging models based solely on efficiency or time may not fully capture foraging strategies.
• An integrative approach combining ecological, physiological, and cognitive perspectives, guided by optimality principles, is crucial for understanding foraging.