Two years later he teamed up with the artist Donald Watson to develop the UK Hen Harrier Winter Roost Survey.[1]The thesis for Clarke'sPhDinbiological sciences, awarded by theUniversity of Liverpoolin 1999, was onbird of preyfeeding ecology.[1][2]Working for theUniversity of Aberdeen, Clarke focused onOrkneyhen harrierfeeding.[1]He also contributed to the controversial Joint Raptor Study Langholm Project, studying the predation ofred grousebyhen harriersandperegrine falconsin southwestScotland's border country.[1]