This blog post was written by “Sid the Spotter”, a member of the VFAS Young Birder’s Club, a special group of kids with a focused interest on birdwatching and nature. Thanks to Sid for his nestbox monitoring and for his great spotting on VFAS outings!

How to get bluebirds?

1) Make a Bird Box

2) Put it up

That’s it!  You’ve attracted bluebirds to your backyard in just 2 steps!

Unfortunately, increasing the bluebird population is not that simple.  It is crucial to monitor the nest boxes.  If you don’t, it might do more harm than good by attracting invasive species such as House Sparrows that are displacing our native birds such as bluebirds.

Early last July, I went to Norristown Farm Park in Montgomery County to learn about monitoring bluebird boxes and do a bit of monitoring myself.

The park currently monitors 110 bluebird boxes. They have been monitoring these boxes since the early 2000s. Each week volunteers there examine the bird boxes and note down things like:  date, box number, species, number of eggs, number of chicks, age, and anything else relevant.  I was fortunate enough to meet with a volunteer so I could learn about this important job.

Right off the bat, I noticed something peculiar. The bluebird boxes had a little slot-shaped opening at the top.  I was used to seeing circular openings.  It turns out that the slot is an emergency escape route in case of a House Sparrow attack.  (House Sparrows are aggressive and will kill bluebirds in order to take over the nesting box.)  If a House Sparrow were to fly into the box, the bluebird inside would still be able to get out alive.

As we approached the first box, the volunteer monitor stepped up to the box and… knocked on it?   Here’s a knock-knock joke for you.


“Who’s There?”

“A Bird Box Monitor”

“A Bird Box Monitor Who?”

“A Bird Box Monitor who knocked on your house, so you aren’t surprised when I open it.”

Monitors will almost always knock before opening. The only time they don’t is when there are older nestlings who are close to fledging in the box.  This is so the chicks don’t jump out early and become prey to other animals.

We continued to walk to the next box.  As I viewed many other bird boxes I was able to see the different nests and eggs of each bird.  I was amazed by the diversity of nest-building techniques.  Can you identify the nests in the below pictures?  Whose nests are these?

Answer: House Wren, Tree Swallow, and Eastern Bluebird

Here is how you can tell the differences:

Bluebird nests

○ Grassy

○ Cup-shaped

○ Blue eggs, occasionally white eggs

○ Usually lays 4-5 eggs

Tree Swallow nests

○ Grassy

○ Cup-shaped

○ Often lined with feathers

○ White eggs

○ Lays 4-7 eggs

House Wren Nests

○ Full of sticks

○ May have decoy nests.  (If you find them, clean them out.)

○ Messy with a nest in the back

○ Brown eggs

○ Lays 5-7 eggs

Now go back and try to re-identify the nests.

Unfortunately, there are invasive bird species that can take over a nest box. If you find one you must clean the nest box out.  This is important because the invasive species are not native to North America and are displacing our native birds.

House Sparrow Nests

○ A big jumble of everything including sticks, grass, bark, and candy wrappers

○ Speckled eggs ranging in color

○ 4-5 eggs

Fortunately, European Starlings don’t fit through the nest box holes if they are sized correctly.

In addition to birds, other animals like the…  Hey, how did a squirrel get in here?  The problem with Gray Squirrels is that during winter the squirrels will chew at the hole and expand it, which ruins the nest box and allows European Starlings to enter.

Some animals like bird boxes, not for shelter, but as a location to find food.  Raccoons, snakes, mice, ants, chipmunks, and blowflies will eat young birds.  Previously, I have seen a dead bird with Wood Mice in the same box.  Wasps will nest in a box and kill the young birds.  Baffles help deter raccoons, snakes, and mice, and a blowfly screen will help prevent blowflies.  Ants need to be cleaned out the day they are seen.  Even though there are methods to deter these pests, Bluebirds still need our help. Their bird boxes must be cleaned and checked.

Bluebird populations are increasing by 2.4% each year, thanks to the dedication and perseverance of bird lovers.  Research and awareness of Bluebirds is only growing.

The next time you see a Bluebird box remember the work that the monitor did to protect the Bluebirds.