Bluethroat (Luscinia svecica) Science Article 8
Ecological factors may affect levels of extra-pair paternity (EPP) by influencing the costs and benefits of extra-paircopulation. During a 10-year study of a Norwegian bluethroat population, the frequency of EPP has varied extensively (8%-76% nests with EPP, 7%-33% extra-pair offspring among years). Here, we investigate whether socio-ecological factors(breeding density, breeding synchrony) and weather conditions (ambient temperature, precipitation) during the peak fertileperiod explain some of the variation in the frequency of EPP. None of the factors assessed were related significantly to thelikelihood that a nest would contain extra-pair offspring. Among broods that contained at least one extra-pair offspring,however, ambient temperature was related significantly to the frequency of EPP: broods contained more extra-pair offspringwhen the temperature was relatively high during the period of peak female fertility. We suggest that there is a direct linkbetween weather conditions and the level of EPP in this population of bluethroats. Environmental conditions are often harshwhen the birds start to breed, a large proportion of the ground being covered by snow and night temperatures falling well belowzero. It therefore seems likely that there is a trade-off between investment in self-maintenance and extra-pair behavior, whichshifts towards self-maintenance when the weather conditions are severe.
Arild Johnsen, Jan T. Lifjeld, Acta Zoologica Sinica 52(Supplement): 232-234, 2006