 To supply energy needs, hummingbirds drink nectar, a sweet liquid inside certain flowers.Like bees, they are able to assess the amount of sugar in the nectar they drink; they normally reject flower types that produce nectar that is less than 10% sugar and prefer those whose sugar content is higher.Nectar is a mixture of glucose, fructose, and sucrose, and is a poor source of nutrients, requiring hummingbirds to meet their nutritional needs by consuming insects.