Declining food availability, corticosterone, and migratory response in a nomadic, irruptive migrant

Area of Science:

• Animal Behavior
• Endocrinology
• Ecology

Background:

• Facultative migration involves variable movements driven by unpredictable resource changes.
• Corticosterone is a potential mediator of facultative migration due to its effects on activity and metabolism.

Purpose of the Study:

• To investigate behavioral and physiological responses of facultative migrants to food restriction.
• To determine if corticosterone levels correlate with migratory responses and body condition changes.

Main Methods:

• Experiments were conducted on pine siskins (Spinus pinus) subjected to a two-stage food restriction in fall and spring.
• Behavioral changes (activity levels) and physiological changes (corticosterone levels, body condition) were monitored.

Main Results:

• No preparatory physiological changes for migration were observed.
• Food-restricted birds in spring showed increased daytime activity, indicating a migratory response.
• Corticosterone levels increased with food restriction, correlating with body condition decline and increased activity in spring.

Conclusions:

• Declining food availability triggers behavioral changes, particularly increased activity in spring, consistent with facultative migration.
• Corticosterone plays a role in mediating these responses, interacting with the initial energetic state of the bird.
• These findings shed light on the endocrine mechanisms and energetic factors influencing facultative migratory behavior.