A literature review showed that most recent conventional dietary studies of Procellariiformes have used otoliths alone to identify fish prey. Using data from a dietary study of Cory’s Shearwaters Calonectris diomedea, based on 673 regurgitates from adult birds, we quantitatively compared the contribution of otoliths and vertebrae for prey identification and quantification. By using otoliths alone, the importance of the main fish prey was greatly underestimated and several species would have been considered completely absent. Therefore, we strongly recommend the combined use of vertebrae, otoliths and other fish remains in order to improve the quality of dietary studies of seabirds. ; We are also grateful for the support provided by the wardens of the Nature Reserve during our stays. This study was financed by Fundação para a Ciência e Tecnologia (FCT-Portugal) through projects PTDC/MAR/ 71927/2006 and PEst-OE/MAR/UI0331/2011