[1] Microsoft Res, Computat Ecol & Environm Sci, Cambridge, England
[2] Univ Oxford, Dept Zool, Anim Behav Res Grp, Oxford OX1 3PS, England
[3] Univ Auckland, Sch Biol Sci, Auckland 1, New Zealand
[4] Auckland War Mem Museum, Auckland, New Zealand
[5] Natl Inst Water & Atmospher Res Ltd, Wellington, New Zealand
[6] Wildlife Management Int Ltd, Rapaura, Blenheim, New Zealand