Ardea
Official journal of the Netherlands Ornithologists' Union

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Senar J.C. & Pascual J. (1997) Keel and tarsus length may provide a good predictor of avian body size. ARDEA 85 (2): 269-274
Body size is a key measure in many studies. The first principal component using various skeletal measures (skeletal PCI) is commonly considered as the best indicator of body size. In practice, external body measures are used to predict body size, because skeletal measures are hard to obtain in the field. Hitherto, however, external measures could not explain more than 40-60% of the variation in skeletal PC1. Here we use a sample of 36 Serin Serinus serinus specimens to obtain an external measure of body size which shows a high correlation with skeletal PC1, has low measurement error, and is easy to measure in the field. Stepwise multiple regression of skeletal PC1 (dependent variable) on different external measures revealed keel and tarsus length as the best subset of predictors. The two variables accounted for 76% of the total variance in skeletal PC1. This was a substantial improvement over the use of traditional measures (e.g. tarsus, wing and tail length), which only accounted for 63%. We confirm therefore the previous suggestion of using external keel length as a good predictor of overall body size, especially when it is used together with tarsus length. The sum of the two standardized variables can be used as a simple and reliable predictor of avian body size.


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