Rothamsted Research receives grant aided support from the Biotechnology and Biological Sciences Research Council. J.G.C acknowledges G. Gaibani and C. Celada from LIPU and the Italian Ministry of Environment for its financial support provided in 2008. The work on Scopoli’s shearwaters was part of the marine IBAs project carried out by LIPU. V.H.P. acknowledges the support provided by the Portuguese Foundation for Science and Technology (SFRH/ BPD/85024/2012). The work on Cory’s shearwaters was part of the marine IBAs project (LIFE04 NAT/PT/000213) carried out by SPEA.