Endocrine patterns during aging in the common tern (Sterna hirundo)

Area of Science:

• Avian endocrinology
• Reproductive biology
• Gerontology

Background:

• Aging impacts reproductive physiology across species.
• Understanding age-related endocrine changes in wild populations is crucial for conservation.
• Common terns (Sterna hirundo) are long-lived seabirds suitable for aging studies.

Purpose of the Study:

• To investigate age-related changes in plasma hormone concentrations (estradiol, progesterone, androgen, luteinizing hormone) in breeding common terns.
• To determine if endocrine profiles correlate with reproductive timing and aging in this species.
• To assess hormonal stability and potential declines in very old breeding individuals.

Main Methods:

• Blood samples collected from known-age breeding common terns over two seasons.
• Hormone levels (estradiol, progesterone, androgen, LH) analyzed in relation to bird age.
• Reproductive parameters, specifically laying date, correlated with age and hormonal status.

Main Results:

• A significant inverse correlation between age and laying date was observed in both sexes; older birds nested earlier.
• Plasma luteinizing hormone (LH) increased in mature females (>5 years).
• Maturing males (3-5 years) showed increasing androgen levels and declining progesterone, while mature males had stable levels. Older birds (16-21 years) showed non-significant declines in estradiol and androgens.

Conclusions:

• Common terns exhibit age-related endocrine shifts, particularly during maturation, influencing reproductive timing.
• Mature common terns maintain relatively stable endocrine status up to at least 21 years.
• Individual variability in hormone levels is high, potentially masking subtle age-related changes in the broader breeding population.