 In animals, recoil motion resulting from underwater propulsion can destabilise trajectory and decrease locomotory performance. The posture of diving seabirds fluctuates simultaneously with their appendage beat, especially in the vertical plane, because of the recoil force of the beat. Seabirds that fly and swim face trade-offs between maximising their locomotory performance in one medium relative to the other, and flightless penguins were hypothesised to have higher underwater pitching stability than alcids that fly and swim. To test this hypothesis, we investigated the in situ pitching stability of three species of diving seabirds, including a penguin, Pygoscelis adeliae, and two species of alcids, Cerorhinca monocerata and Uria lomvia. A high-resolution gyroscope data logger was attached to the back of each bird and recorded the angular velocity of the body during the descent phase of dives.