Original:  Professor Mike Harris, Emeritus Research Fellow at the Centre for Ecology  Hydrology, said that the birds spend eight months at sea, and some don't return, which may be the cause of the lowering population.
Revised:  Professor Mike Harris, Emeritus Research Fellow at the Centre for Ecology and Hydrology, said that the birds spend eight months at sea, and some don't return, which may be the cause of the lowering population.
Edit intent: coherence