Citation: Sandvik, H. (2001) Sexing animals using biometry: intra-pair comparison is often superior to discriminant functions. Fauna Norvegica, 21, 11–16.
Key words: Sexing, biometry, discriminant function, random mating, Rissa tridactyla.
Abstract:
In sexually monomorphic animal species it is difficult to sex unknown individuals.
The most widely used method of sexing in those cases is discriminant analysis.
In species that are socially monogamous and have biparental care, however,
there exists another method which utilises the intra-pair difference in the trait
used in sexing. Equations for calculating the fraction of wrongly sexed individuals
using both methods are given and used to show that the latter method is more exact than
discriminant analysis. The advantages and limits of both methods are compared.
Field data from the kittiwake (Rissa tridactyla) are used to exemplify the
intra-pair comparison method, and to test the assumptions underlying this method for
this species. Among other things, it is shown that kittiwakes display random mating
with respect to head+bill length. Sexing kittiwakes at Hornøya, northern Norway,
by intra-pair differences in head+bill length gives correct results in 96% of the cases.
Full text: © 2001 Norwegian Institute for Nature Research. If you accept (i) that further reproduction, and all further use other than for personal research is subject to permission from the publisher (NINA), and (ii) that printouts have to be made on recycled paper, you may download the article here (pdf, 0.5 MB).