The relationship between the elephants and the birds is called commensalism.
Commensalism is a relationship between two organisms of different species in which one organism benefits from the other, and the other is neither harmed nor benefited. This type of relationship usually occur between a larger host, and a smaller commensal (the organism that benefits from the relationship). The commensal can benefit by obtaining nutrients, or shelter from the host organism, which is not affected. From the question given, the small birds obtain their food from the elephants, and the elephants do not benefit, and are not harmed in the relationship. This relationship is an example of commensalism.
