Fun with Science Club®


			Brothers and sisters fight for food. Carrie Straight 05.03.01 Throughout the animal world, brothers and sisters fight and compete for food. This competition can mean the life or death of a baby animal and is therefore very important for an animal’s survival. Animal parents only have so much food to bring to the young. For instance, parent birds spend a lot of time hunting, bringing food to the young, and defending the nest site. As the number of young in a nest increases, the adults have to decide which nestlings to feed. Some scientists wanted to study sibling competition in marsh tits (Parus palustris). These small birds nest in cavities or nestboxes. The scientists recorded how many nestlings were in a box. They weighed and measured wing lengths of the nestlings every day for 10 days. They could then tell how much weight the young birds gained and how much they grew. They also swapped nestlings between nests, adding more nestlings to some nests and removing some nestlings from other nests. This way the researchers could compare growth rates of nestlings in small broods and those in big broods. They found that in small broods the weight of nestlings was heavier than the weight of broods with their numbers unchanged or enlarged broods. The small broods also grew faster. They also found that in enlarged broods there was a bigger difference in growth rates between the largest and the smallest nestling. The smallest nestlings grew much slower than their larger nest-mates, but wing length did not differ. It seems, some nestlings are better at getting fed than their nest-mates. The less competitive nestlings put their energy into wing development. This might be because if their larger nest-mates leave the nest, they must be able to leave soon also or they might get left behind.


			Nilsson, Jan-Ake and Anna Gardmark. 2001. Sibling competition affects individual growth strategies in marsh tit, Parus palustris, nesltings. Animal Behaviour 61: 357-365.