tailieunhanh - Blackwell Science, Ltd Group breeding dramatically increases reproductive success of yearling but not older female scrubwrens: a model for cooperatively breeding birds?

In some countries, adolescents are less likely than adults to obtain skilled care before, during and after childbirth. 8,9 WHO’s recommendations for increasing the use of skilled antenatal, childbirth and postpartum care are informed by one graded study, one ungraded study, existing WHO guidelines and the collective experience and judgment of a panel of experts. The studies were conducted in Chile and India. One intervention was a home visit programme for adolescent mothers. Another was a cash transfer scheme contingent upon health facility births. Collectively, these studies suggest that interventions to increase the use of skilled antenatal, childbirth and postpartum. | Journal of Animal Ecology 2001 70 370-385 Group breeding dramatically increases reproductive success of yearling but not older female scrubwrens a model for cooperatively breeding birds ROBERT D. MAGRATH Division of Botany and Zoology Australian National University Canberra 0200 Australia Summary 1. Many studies of cooperatively breeding birds have found no effect of group size on reproductive success contrary to predictions of most adaptive hypotheses. A model is proposed for variation in group-size effects group size has a reduced effect on success when conditions for breeding are good such as in good environmental conditions or in groups with older breeders. This hypothesis is tested with a case study of white-browed scrubwrens Sericornis frontalis and a review of the literature. 2. The scrubwren is a cooperatively breeding passerine with male helpers. Previous analyses revealed no effect of group size on reproductive success but those analyses were restricted to groups with older females Magrath Yezerinac 1997 . Here 7 years data are used to contrast the effect of group size on reproductive success for yearling and older females. 3. Yearling females breeding in groups had more than double the seasonal reproductive success than those breeding in pairs even after controlling for territory quality. However group size still had no effect on the reproductive success of older females. Yearling females tended to survive better in groups but older females tended to survive better in pairs emphasizing this pattern. 4. Yearlings breeding in pairs were more likely to be found on poor-quality territories than those breeding in groups exaggerating the already-strong effect of group size on yearling success. Older females were not affected significantly by territory quality. 5. Group size territory quality and female age affected different components of seasonal reproductive success. Group size increased the success of individual nesting attempts while both territory quality

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