In this question, there are no options given to choose from. So i would answer this question based on my knowledge. The most likely cause of the observed variation is adaptation and evolution. The birds of that island adapted to the food source and then they evolved as per the requirement of the place and food source.
It is called Epiglottitis.
I think the answer would be 52cm:24cm ratio but don't take my word for it
It is described as relatively non specific
