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<span>It is common for some toddlers to be very shy and not be sociable. This is due to the fact that they may not have any other siblings at home and do not get out much. The fact that other children play just fine is not alarming as everyone is different than others.</span>
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.