Territoriality of cooperative breeding pukeko (Porphyrio melanotus melanotus) under low and high population density conditions

Abstract

Habitat saturation, due to high population density, and predation pressure have both demonstrated to influence the formation of some social systems. For example, helper-at-the-nest systems are formed when offspring delay dispersal due to a lack of suitable territory availability or high cost of dispersal. In one cooperative avian species, the pukeko (Porphyrio melanotus melanotus), a previous comparison between high density (North Island) and low density (South Island) populations found that at high density, there were fewer dispersal opportunities due to habitat saturation resulting in increased relatedness amongst group members. Climatic variations between the North Island and the South Island could explain many of the results previously found. The recent decimation of a large pukeko population at a North Island site provided us with a unique opportunity to compare group structure between two populations under similar climatic conditions to determine whether or not individuals bred independently in a low density population. For my thesis I aimed to answer three questions. First, how does population density affect the dispersal of offspring from their natal territory? Second, how does population density affect relatedness of adult group members? Third, how does density affect territory size? In this thesis I was unable to determine whether or not dispersal events were occurring or if there was high or low relatedness amongst group members. Territory sizes were significantly smaller at Tawharanui over Shakespear but they were not significantly correlated with group size. Harrier presence was significantly different between paddocks.