Hormonal responses to removal of a breeding male in the cooperatively breeding white-browed sparrow weaver, Plocepasser mahali.

The white-browed sparrow weaver (Plocepasser mahali) is a cooperatively breeding Ploceid finch that lives in groups of up to 11 individuals. Each group consists of a dominant breeding male and female and a varying number of nonreproductive birds that help feed young and defend the group territory. Experimental removal of the dominant male resulted in attempts by other males to take over the group. Removal of a subordinate, nonbreeding male, as a control, resulted in no change of status among group members. During takeover, there was a transitory increase in plasma levels of luteinizing hormone in the new dominant male, but no change in testosterone levels. As reported in previous investigations, dominant males tended to have higher levels of testosterone than females or subordinate males, but this was not related to the heightened aggression of the takeover. Plasma levels of luteinizing hormone, testosterone, and corticosterone did not differ between the other status groups. The possibility that luteinizing hormone, or a hitherto unidentified androgen, may regulate aggression in the white-browed sparrow weaver is discussed.

Behavioral and endocrine correlates of multiple brooding in the semicolonial house sparrow Passer domesticus. I. Males.

Behavioral and endocrine changes associated with reproductive events were studied in free-living male house sparrows (Passer domesticus). Circulating levels of luteinizing hormone (LH), testosterone (T), and dihydrotestosterone (DHT) were maximal during egg-laying and declined during incubation and the first 2/3 of the nestling stage. As the young approached fledging, levels of LH and T rose to levels similar to those of the first egg-laying stage. This pattern was repeated three to five times during the prolonged breeding season of this species. Multivariate statistical analysis demonstrated that elevated levels of LH and androgens during egg-laying stages were associated with high rates of intrusion at nests by conspecifics, especially other adult males, and elevated levels of agonistic activity, nest defense, and mate-guarding behavior by breeding males. Feeding rates of males declined significantly as plasma levels of T began to rise. Concentrations of corticosterone (B) were high during each egg-laying and nestling stage and were correlated with high or rising levels of reproductive hormones. This suggests that reproductive activity, while energetically demanding, was not overly stressful to these birds. Body mass and fat depots were lowest during the final brood of the season. We suggest that the temporal pattern of circulating levels of T in male house sparrows is an adaptation which compromises between two conflicting selective pressures: a high level of male-male competition for limiting nesting sites in a semicolonial setting, and a strong demand for parental care associated with large broods of altricial young.

Behavioral and endocrine correlates of multiple brooding in the semicolonial house sparrow Passer domesticus. II. Females.

Behavioral and endocrine changes associated with reproductive events were studied in free-living female house sparrows (Passer domesticus). Circulating levels of luteinizing hormone (LH) and estradiol (E2) were maximal during egg-laying, declined during incubation, and began to rise during the nestling stage. This pattern was repeated three to five times during the prolonged breeding season of this species. Multivariate statistical analysis demonstrated that elevated levels of LH and E2 were associated with maximal sexual activity, high rates of intrusion at nests by conspecifics, and elevated rates of agonistic activity. Patterns of sexual activity varied during the season and perhaps reflected differing strategies for protecting paternity adopted by the male. Curiously, elevated levels of testosterone (T) and dihydrotestosterone (DHT) were not associated with high levels of intrusion or agonistic response, but rather were associated with incubation stages. As in males, concentrations of corticosterone (B) were high during each egg-laying and nestling stage and were associated with high or rising levels of reproductive hormones, suggesting that reproductive activity was not overly stressful to these birds. Body mass and fat depots declined during the season and may regulate termination of reproduction. It appears that access to abundant food resources found in association with human dwellings allows house sparrows to maintain reproductive activity longer than most other temperate-zone dwelling bird species.