isäntälintu

The term isäntälintu, a Finnish word, translates to "host bird" or "master bird." It refers to the bird that is parasitized by a brood parasite, such as the cuckoo. In brood parasitism, the parasite bird lays its eggs in the nest of another species, relying on the host bird to incubate the eggs and raise the young. The isäntälintu is therefore the unwitting caregiver for the parasite's offspring.

The behavior of the isäntälintu is crucial to the survival of the brood parasite's young. The host bird will typically feed the parasite chick even after it hatches, often recognizing it as its own. In some cases, the parasite chick may hatch earlier than the host's own eggs and may even eject the host's eggs or young from the nest. This places a significant energetic and reproductive cost on the isäntälintu.

Different bird species have varying levels of resistance or susceptibility to brood parasitism. Some species may have evolved defenses, such as recognizing and rejecting foreign eggs, or abandoning parasitized nests. However, brood parasites often evolve counter-adaptations to overcome these defenses. The relationship between the isäntälintu and the brood parasite is a classic example of an evolutionary arms race, where each species exerts selective pressure on the other. Common examples of isäntälintu species include various warblers, pipits, and reed warblers, which are frequently targeted by common cuckoos.