A Technique for Measuring Precocial Chicks from Photographs

Abstract

Measures of the body size and growth rate of chicks are central to many avian studies (Ricklefs 1983). In some species, growth rate or body size at fledging is correlated with subsequent recruitment into the population (Perrins 1965), indicating that these measures can be important indices of fitness. In nidicolous birds, measures of nestling body size can be obtained simply by visiting nests. However, obtaining growth data for the nidifugous young of precocial birds is often far more difficult. Here I describe a technique for estimating the size of objects in photographs and show how this technique can be used to obtain size and growth measures for chicks, especially the swimming chicks of aquatic species that can be approached with floating blinds (Nuechterlein 1982). I then demonstrate the accuracy and utility of this method using data collected from both captive and free-ranging American Coot (Fulica americana) chicks. ' Received 13 July 1993. Accepted 3 February 1994. 2 Present address: Kananaskis Field Stations, University of Calgary, 2500 University Dr. N.W., Calgary, Alberta, T2N 1N4, Canada. SHORT COMMUNICATIONS 805