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Proximate and ultimate factors explaining floating behavior in long-lived birds
1Department of Conservation Biology, Estación Biológica de Doñana, Spanish Council of Science CSIC, 41092 Sevilla, Spain. julioblas@ebd.csic.es
Hormones and Behavior
|November 7, 2009
Summary
Young male and female black kites, known as floaters, exhibit distinct reproductive strategies. Males mature sexually regardless of social cues, while females delay ovarian maturation until pair bonds form, reducing physiological costs.
Area of Science:
- Avian ecology
- Reproductive endocrinology
- Behavioral ecology
Background:
- Avian populations include reproductive individuals and non-breeding
- floaters,
- whose physiology and behavior are poorly understood.
- Delayed breeding significantly impacts fitness.
- Understanding floater status determinants is crucial for avian population dynamics.
Purpose of the Study:
- To investigate the endocrine function as a determinant of floater status in black kites (Milvus migrans).
- To compare the endocrine profiles of non-breeding floaters with reproductively active individuals.
- To test hypotheses regarding the physiological constraints on reproduction in floaters.
Main Methods:
- Long-term monitoring of a black kite population.
- Combination of endocrine, behavioral, and life history data.
- Measurement of systemic testosterone, progesterone, and estrogen levels.
Main Results:
- Non-breeding male floaters showed similar testosterone and progesterone levels to breeding males.
- Floating females exhibited reduced but parallel-timed estrogen and progesterone levels compared to breeders.
- Floaters are not physiologically incapable of reproduction, but the decision is sexually dependent.
Conclusions:
- The cost-benefit balance of achieving full gonadal function differs between sexes.
- Males may benefit from attaining sexual maturity to improve breeding prospects.
- Females may delay ovarian maturation to reduce physiological costs until pair bonds are established, aligning with social monogamy roles.
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