Noninvasive methods for measuring and manipulating corticosterone in hummingbirds

Area of Science:

• Avian physiology
• Endocrinology
• Stress response research

Background:

• Vertebrate stress response is crucial for energy management.
• Hummingbirds are valuable models for energy balance but difficult to study hormonally.
• Corticosterone (CORT) is the primary stress glucocorticoid in birds.

Purpose of the Study:

• To develop noninvasive methods for measuring and manipulating corticosterone (CORT) in hummingbirds.
• To validate cloacal fluid (CF) as a reliable sample for CORT analysis.
• To establish a method for experimentally altering hormone levels in avian models.

Main Methods:

• Collected cloacal fluid (CF) from unrestrained rufous hummingbirds.
• Measured CORT in CF using radioimmunoassay without extraction.
• Used CF creatinine to correct for hydration status.
• Administered exogenous CORT in artificial nectar to assess dose-dependent changes.

Main Results:

• CF CORT levels mirrored plasma CORT responses to stress, with a delayed reaction.
• CF CORT measurements were validated and corrected for hydration using creatinine.
• Exogenous CORT administration via nectar resulted in predictable, dose-dependent changes in CF CORT.
• CF sampling proved noninvasive and did not induce a stress response.

Conclusions:

• Cloacal fluid is a viable, noninvasive matrix for measuring and manipulating corticosterone in hummingbirds.
• This method facilitates frequent sampling without stressing the birds, aiding energetics and stress studies.
• The technique offers a nonstressful, temporally sensitive approach for experimental hormone manipulation in avian models.