Burkhardt, Richard W.: Patterns of behavior: Konrad Lorenz, Niko Tinbergen, and the founding of ethology. Chicago 2005. Internet: https://books.google.de/books?id=NW0jvr2enWQC&printsec=frontcover&dq=Patterns+of+Behavior.+Konrad+Lorenz,+Niko+Tinbergen,+and+the+Founding+of+Ethology&hl=en&sa=X&ved=0ahUKEwjfr9emkrrTAhWCXBoKHabHBRMQ6AEIJDAA#v=onepage&q&f=false.