When one thinks of relationships in the animal kingdom, one usually thinks of the relationships between lions and gazelles, or wolves and sheep. However, even in the most unlikely animals, relationships can be found in which all benefit.
An example of this is the Red-billed Firefinch and the Steelblue Widowfinch.
All Widowfinches are so-called brood parasites that have their eggs hatched by other birds. The newly hatched foreign chicks are usually larger and stronger than those of the parasitised species and it is not uncommon for the smaller chicks to be pushed out of the nest by the parasite.
This is not quite the case for the Red-billed Firefinch and the Steelblue Widowfinch. The Steelblue Widowfinch has chosen the Red-billed Firefinch as a foster parent; but the small bird does not seem to be bothered by this. The widowfinches even lay their eggs in the nests when the parents are present. The
larger number of chicks acts as a superstimulus for the Firefinch. Because of this, both parents gather even more food for the offspring and the likelihood of the parents abandoning their nest is greatly reduced. Thus, the widowfinch causes the survival probability of all chicks to increase and all benefit
from the relationship.
