Birds arrange eggs to detect disturbance.

Some birds lay their eggs in another bird’s nest to hatch.

A lot of the time, the unsuspecting owner of the nest incubates and takes care of the intruder’s egg.

Nesting birds do have ways to differentiate between their own eggs and the intruder’s.

While color, size and shape can be a dead give away that an egg is different from the other eggs in the nest, a recent study reveals that some birds arrange their eggs in a certain pattern to tell if the nest has been disturbed in their absence.

Researchers in New Zealand put model clay eggs in the nests of blackbirds and song thrushes.

Birds that had consistent arrangements were better at identifying and rejecting the foreign objects from their nest.

There are two scientifically hypothetical explanations for the host bird’s acceptance of a different bird’s egg.

One posits that the host birds haven’t evolved the defense mechanisms to fight against the parasites.

The other theory is that the risk of accidentally rejecting their own egg instead of the parasitic egg is too high for the host birds.