Methodological considerations for measuring glucocorticoid metabolites in feathers

Area of Science:

• Avian physiology
• Endocrinology
• Ecological stress monitoring

Background:

• Feather corticosteroid metabolites (fCORT) are increasingly used to assess avian stress.
• Significant methodological challenges exist in accurately measuring fCORT.
• The small sample artifact and antibody cross-reactivity raise concerns about fCORT reliability.

Purpose of the Study:

• To address current methodological issues in fCORT measurement.
• To verify the small sample artifact and explore correction methods.
• To identify hormone metabolites in feathers and assess antibody cross-reactivity.

Main Methods:

• Verified the small sample artifact across species and feather types.
• Attempted to correct for the artifact by adjusting methanol:feather extraction ratios.
• Used high-performance liquid chromatography (HPLC) to identify feather metabolites and tested antibody cross-reactivity.
• Correlated fCORT with fecal glucocorticoid metabolites in house sparrows.

Main Results:

• The small sample artifact persisted across species and feather types, even with adjusted extraction ratios.
• HPLC analysis confirmed antibody cross-reactivity with various corticosterone metabolites, not just corticosterone itself.
• No correlation was found between fCORT and fecal glucocorticoid metabolites in house sparrows.

Conclusions:

• Researchers should be cautious when interpreting fCORT in wild birds.
• Current fCORT measurement methods may not accurately reflect physiological stress.
• Alternative validation methods are needed to establish species-specific relationships between environmental challenges and fCORT.