The effect of investigator activity on Black-legged Kittiwakes (Rissa tridactyla) was assessed using the disturbance caused by an ongoing intensive study investigating chick growth and adult mass loss. Though the effects were small, investigator disturbance decreased adult nest attendance and increased daily chick loss rates. Whereas overall chick survival until day 18 post-hatch was significantly lower in the high-disturbance plot in the first year of the study, it was substantially higher in the second year. We hypothesize that changes in predator activity as an indirect consequence of disturbance were responsible for this pattern. Herring Gulls (Larus argentatus) which nested near the high-disturbance plot and are the main predator of kittiwakes in our study area may have been more susceptible to the effect of disturbance than the kittiwakes themselves. There was otherwise no statistically significant impact of disturbance on chick growth, or on adult kittiwakes extending into the following year. Biases in studies of kittiwakes due to investigator disturbance may thus be negligible when the study is carefully designed. Future studies investigating effects of disturbance on birds should, however, include data concerning potential predators of the focal species and include more than one low-disturbance plot, and should be carried out over two or more years.