Measurements

Males average larger than females in all measurements (see Appendix). Considerable geographic variation in size, but exact patterns difficult to delineate because of lack of data from large portions of range. Wing longer in subspecies on West Coast of U.S.; shortest in subspecies in tropical areas. Bill tends to be longest in northern, central Caribbean, and Mexican subspecies and smallest in South American birds. Tarsus longer in West Coast and central Caribbean subspecies; shortest in South American forms. Measurements of North American subspecies given in Appendix .

Little information for most subspecies; most data are from breeding birds or hunter-killed birds taken in autumn (see Appendix). Mass shows considerable variation among sexes, subspecies, and times of year. Mass lowest after stresses of breeding and Prebasic molt and greatest during midwinter (Eddleman 1989). Mass of male yumanensis in Arizona (mean [g] ± SD): 270.9 ± 31.8 (range 207–319, n = 19) during early breeding season (Mar–Apr); 257.9 ± 31.9 (range 166–336, n = 58) during late breeding season (May–Jul); 268.2 ± 38.9 (range 206–344, n = 17) during postbreeding season (Aug–Oct); and 311.7 ± 24.6 (range 259–347, n = 14) during winter (Nov–Feb; WRE). Suggests that mass data must be interpreted in light of time of year.