The brownish - head cowbird is never going to come through any parenting award . Like the more notorious cuckoos , these shuttle arebrood parasitesthat lay their eggs in other birds ’ nest and let the clueless foster parent feed and raise their chicks . They ’re defaulter for sure , but raw research suggests that they do n’t altogether abandon their infant , and keep an eye on them after they hatch for the welfare of their succeeding siblings .
Scientists used to think that cowbirds place their eggs and then completely forgot about them , but that might not be the case . Cowbird mommy have impressive spacial memory board , says ecologist Jeffrey Hoover , and ante up tending to their legion ’ nests for at least a little while after parasitizing them to ensure their testicle are accepted and not give away as intruders . If the nut are rejected , they ’ll return to the nest and put down the hosts ’ egg inretaliation . After uncovering these “ mafia ” behaviors , Hoover wondered just how long the boo keep tabs on host nests , and if they might keep coming back to hosts that they see raising their kids right .
To find out , Hoover ’s squad set up a large , long - term study . In 1994 , they set up 1000 nest boxes in southern Illinois and monitored theprothonotary warblersthat made their base in them . For the next 20 yr , they check in on the nest every few days during breeding season , pull in note of any attempts by cowbirds to parasitize the nest , the number of cowbird and warbler egg and chicks they contain , and the number of chicks that fledge and leave the nest . They also control some nests , removing the cowbird eggs from different nests during dissimilar years to mime rejection by the surrogate parents .
Theyfoundthat cowbirds were much more likely to pass to nests that successfully elevate cowbird chicks to independence and parasitize them again . Meanwhile , nests where cowbird chick did n’t fledge , either because of natural occurrences or because the research worker removed the nut , were less likely to get return visits .
“ We attest that cowbirds can discriminate between areas of eminent and humbled cowbird productiveness within a exclusive host species even while pick out among uniform nest site , ” the researchers publish . The parasite are n’t choosing hosts based just on habitat or nest characteristic , but on the foster parents ’ performance raising little cowbirds . Manipulating the nests over time also evince that the birds update their pick free-base on the latest data .
“ This pattern implies that cowbird females are monitor their reproductive output to inform next breeding decisions , ” the team sound out . They learn from the success or failure of one hold of eggs to aid them beak the best parents for the next one .
The investigator ca n’t be certain that it ’s the same female parent birds targeting the same nest class after year , but it would make signified that each bird keeps track of their own chicks ’ achiever and draws on that personal entropy for next time . They suppose that the cowbirds might also use “ social data , ” and keep tabs on nest where other cowbirds have laid their eggs so they can swoop in on productive nests that they have n’t examine yet . In these cases words , the cowbirds are n’t just brood leech , but also information sponge , case the nests of other cowbirds ’ hosts to pile up intel .
