Feeding of nestling and fledgling brood parasites by individuals other than the foster parents: a review

We summarize 67 reports of 13 species of brood-parasitic young, mostly fledglings, being fed by individuals other than the host. We refer to this behavior as auxiliary feeding. The parasite gains extra food resources, whereas the adult that feeds the parasite appears to behave maladaptively. The parasite may present a supernormal stimulus, manipulating unrelated adults into feeding it. Most auxiliary feedings were observed in brood parasites that were raised by small hosts. Host specificity, vocal mimicry, visual mimicry, and nestling competition apparently were not associated with the number of records of auxiliary feedings; however, the trends could not be analyzed statistically because of the anecdotal nature of the observations for each species. Still to be determined is whether obtaining auxiliary feeding is a strategy used by some brood-parasitic species, particularly the pallid cuckoo (Cuculus pallidus).