In 1964 he and his wife moved to Washington State University and joined Donald Farner's group investigating photoperiodism. That became his main research for 40 years with the focus being on the brain pathways whereby birds (and mammals) measure daylength and use its changes to regulate breeding. He took up a lectureship at Leeds University and moved with James Dodd FRS to the University of Bangor in 1969, and from there to the University of Bristol in 1978. He moved to Warwick in 1993 as Vice-Chancellor.