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Related Experiment Videos

Repeatability of baseline corticosterone concentrations.

L Michael Romero1, J Michael Reed

  • 1Department of Biology, Tufts University, Medford, MA 02155, USA. michael.romero@tufts.ed

General and Comparative Endocrinology
|November 27, 2007
PubMed
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Hormone levels in birds are not always consistent, challenging assumptions in endocrine research. Individual hormone rankings varied significantly between day and night, especially under long days or during molt.

Area of Science:

  • Endocrinology
  • Animal Physiology
  • Behavioral Ecology

Background:

  • Endocrine studies often assume consistent individual hormone levels for reliable data collection.
  • This assumption is critical for field studies where animals are sampled infrequently.
  • Glucocorticoids, like corticosterone, are key stress hormones often studied in this context.

Purpose of the Study:

  • To test the assumption of consistent individual hormone titers in house sparrows (Passer domesticus).
  • To investigate how photoperiod and molt affect the reliability of individual corticosterone level rankings.
  • To determine if individual hormone profiles are consistent across different times of day and experimental conditions.

Main Methods:

  • Captive house sparrows were used in a controlled laboratory setting.

Related Experiment Videos

  • Baseline corticosterone titers were measured five times per bird.
  • Measurements were taken under short day, long day, and prebasic molt conditions, during both day and night.

    • Main Results:

    • Individual corticosterone variation within birds often exceeded variation between birds.
    • Relative individual rankings were consistent at night across all conditions.
    • Daytime rankings were only consistent under short day conditions; long days and molt showed inconsistent rankings.
    • Individual ranks frequently differed between day and night measurements.

    Conclusions:

    • The assumption of consistent individual hormone titers is not universally valid for birds.
    • Diurnal rhythms and physiological states like molt significantly impact hormone level consistency.
    • Researchers must carefully consider sampling time and conditions to avoid misinterpreting interindividual variation in hormone levels.