It is used to detect parasitic eggs from worms like roundworms, hookworms, whipworms, lungworms and tapeworms. (petsmagazine.ca)
The tree sparrow (Passer montanus) seems to have evolved strong variation in egg coloration and size between clutches, probably to enhance its ability to discriminate parasitic eggs from its own. (sciencedaily.com)
The birds removed foreign eggs from the nest in about a third of cases in the first experiment, although the remainder accepted and continued to incubate parasitic eggs. (sciencedaily.com)