Bird Lady Blog

January 1, 2016

Brown-Headed Cowbirds


Brown-Headed Cowbird

Brown-Headed Cowbird

Several readers have told me that birds are building nests on their property, and some have sent photos.  Martha on Reindeer has two nest boxes that are supposed to be for Western Bluebirds but are now occupied by nesting House Wrens.  This particular House Wren in Martha’s photo is bringing in sticks wider than the width of the hole and somehow, either by luck or instinct, manages to get enough twigs fitted through the hole and into the nest box to build her nest.  Cindi and Kathy on Turkey Trail also reported they have nesting House Wrens in one of their next boxes.

Alan and Cheryl on Wildcat sent me a great photo of eye-catching blue American Robin eggs in a nest on their property.  At the time of this writing, the chicks hatched and are growing on a daily basis.  The next photo they sent me was of open baby bird mouths waiting for the proverbial worm, and the third photo showed how they were developing their feathers while still demanding food every time a parent approached the nest.  I think the nest is amazing – all the twigs tightly woven together to make a little cup perfectly fitted for the eggs.

I also heard from Lu and Don who live on Lake Odell, and they had a complaint – too many Brown-Headed Cowbirds dominating their bird feeder area.  Brown-Headed Cowbirds are one bird I haven’t written about before; they have not been high on my list.  They have a unique approach to nest building – they don’t build nests at all and instead lay their eggs in the nests of other birds.  They are considered a parasite because they lay an egg in another bird’s nest, usually a smaller bird like a warbler, sparrow, or vireo, and often they toss out one of the eggs already in the nest.  Brown-Headed Cowbirds hatch faster than the host bird’s eggs, and their chicks are larger, so they compete with the host bird’s babies and often cause them to starve to death.

In years past, Brown-Headed Cowbirds still had a balance in nature; much of the time they were found following herds of buffalo.  But then humans made changes to the landscape by cutting into forests with roads, introducing cattle, and causing deforestation, so the habitat for Brown-Headed Cowbirds changed and made it easier for them to find the nests of host birds, and therefore to multiply.  Cowbirds can lay 30-40 eggs within a breeding season, negatively affecting the nests of that many host birds.  The Brown-Headed Cowbird is considered one of the key reasons for songbird decline in North America.

What can we do to help stop this Brown-Headed Cowbird trend?  On a big picture, the best approach is landscape management – ensuring large tracts of land are available for other native birds and minimizing fragmented landscapes.  On an individual scale, you can use tube feeders with smaller perches and no catch basin at the bottom.  Don’t use tray feeders, and avoid sunflower seeds and cracked corn.  At our home in Munds Park at the edge of Munds Canyon, I have a tray feeder (frequented by Band-Tailed Pigeons) and a sunflower feeder, used by all types of birds, but never frequented by Brown-Headed Cowbirds because our home is in the woods, not in an open area.  At Lake Odell, however, the Brown-Headed Cowbirds stay in flocks with Red-Winged Blackbirds and Brewer’s Blackbirds, so they will be harder to control.  Sticking with a nyger seed feeder, suet feeder, and a peanut feeder is probably the best way to still attract birds and discourage Brown-Headed Cowbirds.  I also have read that Brown-Headed Cowbirds do not favor safflower seeds, which might be good to try as an alternative to sunflower seeds.

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