In their classic paper, «Life History Variation in Primates» published in the premier scientific journal Evolution, the British
zoologists Paul H. Harvey at Oxford and Tim Clutton - Brock at Cambridge published the most comprehensive data then available on the world's primates.
The German
zoologist Paul Leyhausen (1916 — 1998), who spent the bulk of his career studying the behavior of cats, found that cats, frustrated by the difficulties of catching them, «may soon give up hunting birds.»
«Primarily, all cats hunt both birds and rodents with equal zeal,» observed German
zoologist Paul Leyhausen, «and many obviously prefer eating birds.»