Question

Question 17 Not yet answered Marked out of 10.00 Flag question Geese make nests on the ground and sometimes their eggs fall out of the nest. When this happens, they attempt to roll the eggs back into the nest using their bills. When you steal an egg from a goose, and give it a choice of its own egg or a baseball, the goose ignores its egg and tries to roll the baseball into the nest. Given a choice of a baseball and a softball, the goose chooses the softball, and given the choice between a softball and a soccer ball it chooses the soccer ball. Explain in terms of behavioral mechanisms why the goose tries to roll anything at all. What is the evolutionary process that is responsible for the preference of the goose for the larger object, and how does it work in this instance?

Answer 1

This is the typical fixed action apttern of egg retrieval behavior in grelag goose. Its reported by Konrad lorenz and Niko Tinbergen. If an egg becomes displaced from the nest, the goose rolls back its egg to the nest with its beak. The sight of the egg which is displaced is a typical sign stimulus and produces the retrieval behaviour. Goose first fixes its sight on the egg and extends its neck over the egg. And it rolls back to the nest using its underside of beak and if the egg is removed from the goose during their perfomence of egg rolling then, the bird will continue to do this behaviour, pulling its head as if an imaginary egg was present. They show supernormal stimulus when egg shaped ball is given on theie sight and stimulus had to obtain in order to trigger a resulting FAP were given the term of sign stimuli. So an innate deciphering method that goose wents through to determine this suitable sign stimulus. This is called innate releasing mechanism.

This supernormal stimuli exhibited by the goose( responding to ball), provides aclue to natural selection. Since variation exists in nature, and changes in some stimulus features like egg size can result in an increased ability to trigger response selection leads to favoring of genes and leads to more potent releasers. This can be due to phenomenon of discrimination learning known as peak shift. It reflects the action of 2 factors in phylogeny-1) asymmetrical selection pressure with respect to responsiveness to relevant stimulus 2) independent selection pressures limiting corresponding properties of natural stimulus. The evolutionary advantages of this behavior is that its essential for the survival of chicks and the fitness of the parent bird is increased by the behavior being invariant.