Morphology and territory acquisition in willow ptarmigan

Indices of body size, condition, and reproductive status were compared among willow ptarmigan (Lagopus lagopus alexandrae Grinnell) yearlings that held territories and those that replaced them in response to an experimental removal. We wished to determine whether these morphological factors had influenced the acquisition and retention of territories by residents. There was no difference in body size between residents and replacements in either sex, nor was there a difference in comb height, a correlate of hormonal status and aggression. Early replacements were in a condition similar to residents in females, but in poorer condition in males. There was a marked loss in condition in later replacements but this was more likely a consequence of nonterritoriality than a reason for it. We suggest that other factors such as prior familiarity with the breeding area or arriving before others may influence successful territorial establishment.