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Brown-Headed Cowbird: Not Such a Bad Egg After All
Brown-Headed Cowbirds devised their own way to survive and thrive. Because they followed the cattle that stirred up insects, they became nomads. As such, the only way to perpetuate their species was to use the nests of host birds to feed and raise their young for them; most often to the detriment of the host's babies. Thus they have earned the reputation of bringing about the decline of our backyard songbirds. But recent research has painted a much different picture.
Brown-Headed Cowbird: Origin of its Name
Cowbirds were so named for their habit of following the huge herds of buffalo as they grazed on the vast American Plains many years ago. As settlers cleared the land across North America and introduced more grazing animals, the numbers of brown-headed cowbirds expanded. They are the only North American Brood Parasite. These birds had to deposit their eggs quickly and on-the-fly, so to speak. There wasn’t time to build a nest and tend to chicks while also following the animals that kicked up volumes of insects as they moved and grazed. Cowbirds had to become opportunists; finding and using other birds’ active nests was the logical way to insure the continuance of their species.
Male and Female Cowbird Interacting and Singing
Identifying Brown-Headed Cowbirds
They often move within flocks of blackbirds, grackles and starlings as they search grain fields for food sources. Male brown-headed cowbirds have a sleek and shiny black body and a brown head, which shows up best in sunlight. Females are tawny grey without the brown head. Both males and females have a red eye. Their beaks are heavy and conical in shape, and dark grayish brown in color.
Cowbirds communicate using a pleasant gurgling song, peppered with squeaks. Their call is a rattling sound.
Did You Know?
Many songbirds have learned to detect and eject or build a new nest over a cowbird egg. Brown Thrashers, American Robins, Common Yellowthroats and Catbirds are just a few of those who “just say no” to cowbird eggs! In fact, 95% of the time, gray catbirds reject cowbird eggs.
Brown-Headed Cowbird: Not Such a Bad Egg After All!
In years past Nature was able to hold the balance. Now, though, songbirds are losing habitat and nesting sites at an alarming rate. Modern day urban sprawl is the root of the problem, not the cowbird.
- Cowbirds have earned the reputation for bringing about the decline of the songbird population in recent years. However, the latest scientific evidence indicates that cowbird populations are generally declining.
- Additionally, many songbirds can successfully raise their own babies in a second nesting after having been parasitized by the cowbird during the first nesting.
- The songbird may notice the difference between her eggs and the foreign egg, desert the nest, and build a new one somewhere else.
- Some birds like the house finch feed their young a strictly vegetarian diet. Because baby cowbirds need protein to survive and thrive, if a cowbird should choose to deposit her egg in a house finch nest, the baby cowbird won’t make it to adulthood.
- A nest that harbors a cowbird is more likely to become the target of a predator, simply because the cowbird babies are so aggressively noisy; plus the fact that cowbirds pick songbird nests that most commonly fall prey to predators.
- Some songbird babies, like the song sparrow, have learned to ‘change their voices’ to more closely match the cowbird nestling’s sound and amplitude in order to receive as much food as the foreign baby!
Cowbird Mating; Cowbird Eggs
Cowbirds have been documented to use over 220 host species, with more than 140 different species actually raising young cowbirds. Cowbirds are not known for being monogamous. Males and females can have many different mates throughout the breeding season. The courting male will sing a very long song to a female and follow it with a bow, as if on stage!
Cowbird eggs, which are bluish-white with brown speckles, tend to hatch earlier than the host’s eggs, providing a care and feeding advantage. A female cowbird does not build any nest, but deposits one egg (sometimes two) in the nests of native songbirds. She will lay as many as 25 to 30 eggs in a breeding season! The host birds then raise the cowbird as their own. The larger cowbird nestling hatches sooner than its nest mates, and will demand more food. As it grows bigger, the other baby birds are either starved out or kicked out by the baby cowbird .
'Mafia Revenge' Behavior of Cowbirds
Cowbirds may exhibit what is known as ‘mafia revenge’ behavior. First they watch to see where the active nests are located. Once they deposit their egg, they also keep watch to see if it is ejected. Retaliation can be swift and brutal if such an ejection occurs! The other eggs are destroyed. It’s best not to make a cowbird mad!
Did You Know?
Cowbirds are protected by the same laws that cover all songbirds!
Preferred Habitat of the Cowbird
Cowbirds tend to search out overgrown fields and the outside edges of forests. They don’t like the environment inside a forest, and do not seem to bother songbirds living there. When I was young, there was a dirt road between our house and the field used for a neighboring farmer’s dairy cattle. I used to watch as the cowbirds feasted on the bugs those cows kicked up. They put on quite a show as they perched on the cows and then quickly flew out to grab bugs on the wing. That field was prime hunting grounds for lots of birds, including the cardinals.
There was a narrow hedgerow between our property and the neighbor on the same side of our road. In that hedgerow were lots of wild roses, in which the cardinals loved to nest. Rose hips are a prized treat for cardinals as well. Cardinals are a prime target nest for cowbirds! Since there were always lots of cardinals flying to my Mom's bird feeders, I suspect there was a natural balance between the cowbirds and cardinals even then.
You Can Help Songbirds
Cowbirds do not like to enter dense, wide shrubby areas. Lots of songbirds, however, do like just such a habitat. You can help by creating a dense hedgerow in your backyard. Restoring a natural habitat will go a long way towards helping our wonderful songbirds to rebuild their populations.
Chicago's Magic Hedge: Montrose Point Bird Sanctuary is part of a park system that includes a converted US Army Nike missile base. Honeysuckle hedges and sumacs, serviceberries and viburnums were used to camouflage the missile launchers during the Cold War. I am so glad this was transformed for a peaceful bird habitat that serves to shelter many songbirds during their migrations in the fall and spring.
Montrose Point juts out into Lake Michigan and supports woodland, lake dune and prairie habitats that annually attract tens of thousands of songbirds from over 300 different species.
Preferred Foods of the Cowbird
Dandelion, ragweed and other common garden weed seeds, blackberries and huckleberries, cracked corn, tan or red millet, milo, wheat, oats, buckwheat, wildflower seeds and black oil sunflower seeds make up the cowbird diet. Grasshoppers are another favorite snack enjoyed along with ants, caterpillars, flies, beetles, grubs, spiders, crickets and weevils.
Brown-Headed Cowbirds are permanent residents in southern areas of the US; northern residents move to the south and Mexico when the weather turns cold. They return to their northern habitats in late March or early April.
So Is There a Solution to Cowbird Parasitization?
The solution to the cowbird problem lies in better management of agricultural and grazing practices. Restoring natural habitat through use of wide, dense shrub hedges and replanting larger forests with both deciduous and non-deciduous trees will go a long way towards returning the natural balance.