Breeding biology of Muscovy duck (Cairina moschata) under natural incubation: the use of the Weibull function and a beta-binomial model to predict nest hatchability

In this paper we tested the Weibull function and beta-binomial distribution to analyse and predict nest hatchability, using empirical data on hatchabi lity in Muscovy duck (Cairina moschata) eggs under natural incubation (932 successfully incubated nests and 11 822 eggs). The estimated parameters of the Weibull function and beta-binomial model were compared with the logisti c regression analysis. The maximum likelihood estimation of the parameters was used to quantify simultaneously the influence of the nesting behaviour and the duration of the reproduction cycle on hatchability. The estimated p arameters showed that the hatchability was not affected in natural dump nes ts, but in artificial dump nests and in nests with non-term eggs the hatcha bility was reduced by 10 and 25%, respectively. Similar results were obtain ed using logistic regression. Both models provided a satisfactory descripti on of the observed data set, but the beta-binomial model proved to have mor e parameters with practical and biological meaningful interpretations, beca use this model is able to quantify and incorporate the unexplained variatio n in a single parameter theta (which is a variance measure). (C) 1999 Acade mic Press.