The effect of 4.5-g dummy geolocation loggers on the foraging ability of Cook's Petrel (Pterodroma cookii) was assessed over single foraging trips from Little Barrier Island, New Zealand. I compared foraging trip duration and chick provisioning between equipped and unequipped birds and could not detect a detrimental effect of loggers on either parameter. The lack of effect of these loggers may be the result of their small size, the short-term nature of their use, and foraging strategies used by Cook's Petrel. Geolocation studies involving Cook's Petrel and other small gadfly petrel species may be feasible for single foraging trips.