positively correlated with mean nestling mass and tarsus length. The effect on tarsus .... Female inc. mass [51) 14.8 i 0.4 15.2 i 0.6 15.2 i 0.8 1.43 2.27 0.258. Femalc mass (1. ..... of a free~living bird. â J. Anint. Ecol. ... M. and Mailer. A. P. I989.