THE ECOMORPHOLOGY OF SEXUAL DIMORPHISM IN THE NEW-ZEALAND RIFLEMAN ACANTHISITTA-CHLORIS

New Zealand Rifleman Acanthisitta chloris females are larger and brown er than males (which are green dorsally), have a relatively larger hin d claw and a longer, more decurved bill. Using three criteria for dist inguishing sexual selection from ecological influences on sexual dimor phism, we suggest that sexual dimorphism in the Rifleman is maintained by ecological factors. When energy requirements were high (feeding fl edglings), female and male Rifleman foraged separately. When energy re quirements were low (non-breeding), females and males fed together. Pl umage differences between the sexes were correlated with the different habitats in which Riflemen foraged when energy demands were high.