Bluebird Victims

The scene above is one to warm the heart of anyone tending to bluebird nest boxes.  Watching them grow and fledge is the rewarding part of maintaining and cleaning the boxes over the year.  Unfortunately it doesn't always have a happy ending as reported by Mort Shurtz.

"I've been watching our bluebird house for several weeks. First eggs, then a check on the healthy chicks yesterday and everything looked good. This morning I discovered a House Sparrow on the bluebird box. When I inspected the box, all the chicks were gone and the sparrows had built a huge nest in the box. The babies were lying on the ground about 10 feet from the box with holes pecked in their heads"

Mort's Bluebird s- day one

After the attack

The House Sparrow (HOSP) is a native of Europe and Asia which has been transported to Africa, North and South America and Australia, making it the most common bird in the world.  Native species haven't learned to compete with them as they have only been exposed to this threat for a few hundred years.  HOSP thrives in close association with humans which, come to think of it, are also a rather invasive species.

HOSP are common nest predators of small cavity nesting species such as Eastern Bluebirds.  They will peck at the head and eyes, killing chicks and adults alike.  They will also destroy and remove eggs before building their own nest.  I asked Lisa Berger from GOAS* to comment.

"House Sparrows are fierce, nasty competition, negatively affecting many native cavity nesting species.  Bluebirds, Chickadees, Titmice, Tree Swallows, Carolina Wrens, House Wrens, Downy Woodpeckers and others did not evolve with the House Sparrow on the North American continent. The English Sparrow (House Sparrow) was introduced in the new world, soon after European contact: It is, in fact, an invasive species and should be treated as such. Our native NA species do not have strategies (nor have had time to adapt) to compete favorably with invasive species."

Like starlings, HOSP are not protected by the Migratory Bird Treaty Act, which makes it illegal to harm or harass any native species, including their nests and eggs.  For this reason, it is acceptable and even encouraged to remove the nests of HOSP if you are sure that it is the offending species.  Chickadees, wrens and others should be left alone, a nice byproduct of your nest box generosity.  Charley Burwick added this advice:

"On the GOAS Bluebird trails where we have had this problem, we just remove the boxes from the routes. Typically this happens when the Eastern Bluebirds build nests in a too urban area, and the House Sparrows are plentiful. Usually, when we have ran into this issue in more rural areas, it is where there are livestock pens, etc., too close to the boxes." 

*GOAS is Greater Ozarks Audubon Society

Nestwatch.org has some practical measures to discourage sparrows from nesting in birdhouses.

Sialis.org has lots of reports of nest predation by HOSP.  Graphic pictures of the results of a HOSP attacking a tree swallow nest, not for the faint-hearted, are at this Sialis.org link.