|The reports on hybrid lovebirds by Dilger (1962) have often been quoted as examples of how resistant inherited fixed actions of behavior are to change. All species tear strips from leaves to produce suitable nesting material (and will use old newpapers as a substitute in the laboratory). However the peach-faced lovebird on the left above stuffs the strips into its rump feathers before flying back to the nest, while the Fisher's lovebird keeps the material in its beak, like most bird species. It is certainly striking that hybrids between these two species were initially incapable of building nests because they would make unsuccesful attempt to stuff the nesting material in their rump feathers. However, over a period of months they gradually learned to get better at keeping the material in their beaks and Dilger reported that after 6 months they succesfully kept material in their beaks for carying on 41% of their attempts. After two years they were successful 99% of the time. In the description by Manning (1967; p.30) it is stressed that even after 2 years they still made a turning movement of the head which is the preliminary to the stuffing behaviour of peachface species, but the fact that the birds gradually learned to overcome the handicap of having an ineffective combination of inherited behaviour patterns can equally well be used as a good example of the interaction between genetic determination and adjustments (in this case fairly gradual) made as a consequence of learning from experience.
Dilger, W.C. (1962) The behaviour of lovebirds. Scientific American, 206, 88-98.