My husband and I were discussing cow birds this morning; we were wondering how that kind of nest-parasitism develops as a trait. Cow birds will choose any of many kinds of species’ nests; and some females show a preference for a particular species.
I’m no expert but I believe other birds will use a competitor’s nest for hatching their young.
Well, with the cow bird living off the insects picked off of herds of bison, there wasn’t time to fight for a territory, build a nest, incubate and raise chicks before the food source sought greener prairies... so just dropping eggs in a couple local bird’s nests along the way did the trick. The likelihood of the chick’s survival was higher with string of hosts, as there are some species of birds which can recognize an egg that’s not theirs and push it out, while others just aren’t that bright. They practice the adage “Don’t put all your eggs in one basket.”