Cowbirds, though they’re native to our continent, may actually be functioning as an invasive species.
The problem is that as forests in the east were cleared, cowbirds traveled east.
Today, so many roads go through forests (in addition to many other changes in our landscape) that there’s a lot of the edge habitat that cowbirds like. New York’s Adirondack Park is a good example: the many roads running through the park create edge habitat in what had been intact forests.
Birds native to cowbirds’ original range in the prairies had evolved defenses against their nest predation, but many birds native to the east had not.
This small chipping sparrow raised the much larger cowbird baby. I don’t know if the chipping sparrow managed to raise any of her own babies that year.
I’ve never seen a junco raising its own babies in our yard, but I did see a junco raising this cowbird baby.
This cardinal is looking for food in our blueberry area to feed this cowbird baby.
They’re very persistent and very insistent!
Song sparrows seem to be particularly susceptible to nest predation.
Year after year, we’ve watched a poor female song sparrow raise cowbird babies instead of tending to her own babies.
The baby cowbirds quickly grow larger than the sparrows, and she runs herself ragged trying to feed them. The cowbird baby also has a large red mouth (a signal for feeding) and a low, incessant chirp, leaving the song sparrow’s own baby at a distinct disadvantage.
Heartbreaking to watch.
Not so heartbreaking was finding cowbird eggs in the house sparrow nests. This has happened multiple times a season. Poetic justice I guess!
Resources
- Smithsonian Migratory Bird Center:
- NestWatch:
- Cool Green Science:
Reflections
A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise.
~ Aldo Leopold