There have been a couple stories lately about leaving baby animals alone, even if you think they are abandoned, because they may actually be waiting for their mother to return, and your activity could interfere. Birds are a very good example of this behavior. In most cases, if you see a fully feathered baby bird, on the ground or a low tree branch, it is probably there because its mother lured it out of the nest, and is going to bring it food eventually.
Now, let me be clear on something. If you pick up a baby bird and put it back in its nest, its mother will not abandon it. Human scent on a baby does not result in being orphaned. I have to make that clear right off, because your mom probably told you that, just like my mom told me. Sorry Mom. It is fairly likely, though, that a baby bird on the ground was pushed out of the nest by another occupant, and if you put it back in, it may get pushed back out again. This could be the origin of the old wives’ tale. If the bird is not healthy or fit, a parent or sibling eliminating it is basically survival of the fittest. There are other reasons a bird could get ejected, though. It could be blown out by wind, grabbed and dropped by a predator, or the nest could be knocked down. It could get pushed out by an evil baby, as in the case of the cowbird.
Brown-headed Cowbirds lay their eggs in other birds’ nests, a behavior called nest parasitism. They are known to lay eggs in the nests of more than 200 other bird species! The cowbird hatches sooner than the eggs that occupy the nest legitimately, and instinctively pushes the other eggs and babies out of the nest. Bad baby! The result-parents lose their entire nest, and feed and care for the evil baby of another species.
Some bird species, like American Robins, Blue Jays and Brown Thrashers, reject the eggs, or even the nest. Other species, like vireos, song sparrows and warblers, readily accept and hatch the eggs. In fact, there are some bird species that are seeing declines in reproduction and overall population numbers as a result of this cowbird nest parasitism.
Some other bird species “dump nest” which is sort of like parasitism on your own species. Wood ducks are great at this-a hen will crawl into an unattended nest of another wood duck hen, lay an egg, and take off. I have seen wood duck boxes where over 20 eggs were dumped in one box! From what I could tell, the resident hen eventually found something was wrong, and she abandoned the nest. Pheasants are another known dump nester that can parasitize prairie chicken nests.
Some young swapping happens after hatching in the bird world as well. Canada geese sometimes pick up the young of other broods, expanding their own little troupe. Hen turkeys will sometimes join forces, forming “gang broods” that may have three or four hens and a couple dozen chicks, or poults. This helps increase survival of individual chicks and lets populations expand rapidly. On the other end of the spectrum, cranes lay two eggs, and typically only raise one young per pair per year. This is one reason why it has taken so long for suppressed crane populations to recover.
By the numbers, survival of birds from egg to adult is frankly very low. The death of young hatchlings is common and natural. Still, our instinct as humans is to help injured or orphaned wildlife. If you see a young bird that you think needs attention, contact your local wildlife rehabilitator, and they will know what to do. Wild Instincts in Rhinelander is licensed for care of all bird species; call (715) 362-WILD.
Jeremy Holtz is a wildlife biologist with the Wisconsin DNR in Rhinelander, and writes a weekly column in the Star Journal. To contact him, call (715) 365-8999.