The Bluebird Diaries – Day 18 (April 7, 2012)

Ho hum. No activity in the bluebird nest today. They are definitely done building. We’re assuming it’s simply too chilly to lay eggs. They can wait a full week or two after construction to begin laying. This can be good or bad for us. Good of course because it will be warmer and food (insects) will be in better supply. Bad because this blog is going to get mighty boring while we wait! 🙂

The male bluebird would have been happy with a bit of boredom today. He spent much of the day fighting off threats to the nest, perceived and real. The perceived threats were cowbirds and a starling. The starling landed on the roof of the nest box, prompting a bit of a wrestle. The cowbirds generally just hung around checking things out, causing the occasional chase. Starlings and cowbirds can’t fit in the hole of the box so they really don’t threaten the nest, but the bluebirds don’t know that. When bluebirds nest in the wild they sometimes use old woodpecker holes or other cavities that starlings can definitely take over. Cowbirds are parasitic birds, meaning they lay their eggs in other birds’ nest. The “host” bird raises the cowbirds as its own and sometimes everyone survives. Other times the cowbird babies are bigger than the host’s babies, taking most of the offered food from the parents leaving little for the native birds.

Since neither starlings nor cowbirds can fit in the nestbox hole, they pose no real threat. But, the male bluebird still expends effort to chase them off.

Unlike the starlings, house sparrows are a real and severe threat to the success of any bluebird nesting, and we spotted more today than any day so far. They give the name “sparrow” an undeserved bad name, because there are many types of sparrows. Native sparrows (which won’t hurt bluebird nests) include Chipping, White Throated, White Crowned, Song, and Fox Sparrows. They’re all beautiful and interesting and we love seeing them in our yard. The house sparrow, by far the most common, was introduced to the United States in the mid-1800s. This introduction could possibly be the single worst species introduction in avian history, at least where backyard birds are concerned. They gleefully destroy other cavity-nesting birds’ eggs and young, and often even kill the adults. Sometimes they don’t even want to take over the nest. They just don’t want anyone else to have it either.

Today’s house sparrows showed interest in the nest box more than once, landing on the box and occasionally hovering in front of the hole. The male swooped in to chase them off, and he was successful each time. However it’s troubling to see the increase. There’s no problem at the moment, but they can be a big problem once eggs and young begin arriving. The house sparrows tend to become even more aggressive and the bluebirds less able to chase them off. Let’s all keep our fingers crossed these yard visitors find a great food source in another neighborhood soon.

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