How to Tell a Bluebird Nest from a House Sparrow Nest – Complete Guide

So you’ve got a nest in your bluebird nest box. Are you sure it’s a bluebird nest? Or, could it be the invasive house sparrow instead?

Three primary ways to tell a bluebird nest from a house sparrow nest is shape, material, and height. Bluebirds have clean cups of pine or straw that sit below the entry hole. House sparrows fill a box with no defined cup or consistent material. But in many cases you will still need other clues.

The reason it is important to know the difference between a bluebird nest vs. a house sparrow nest is because house sparrows are not native to North America. And they are famous for attacking and killing adult songbirds for their cavity spaces.

As a backyard bird hobbyist who wants to promote native bird species, it is important not to allow house sparrows and European starlings to nest and thrive.

Instead, we want to promote native cavity birds like bluebirds, chickadees, tree swallows, purple martins, fly catchers, titmice, etc.

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Differentiating bluebird nests from house sparrow nests

The key ways of distinguishing a bluebird nest from a house sparrow nest is the shape of the nest, the material the nest is composed of and nest height.

Bluebird nest vs. house sparrow nest: Nest shape

While a bluebird nest will span all four walls of the nest box, there will be a defined cup or bowl shape within the nest. The depth of the cup and its position (whether centered or set closer to a wall) may differ, but once the nest is complete, you will see a true cup.

House sparrows, on the other hand, are famous for tunneling their nests. Rather than seeing a cup formed over the top of the nest, you might see a hole in the side of the nesting material that goes into the nesting space.

Many times, with house sparrows, you may not see a hole at all. When you open the box, what you might see instead is nesting material that fills the entire box all the way up to the roof.

Bluebird nest vs. house sparrow nest: Nest material

Nesting material is a a great way to tell the difference between a bluebird nest and a house sparrow nest.

Bluebirds generally make their nests of straw, tall grass, grass clippings or pine needles. For the most part, the consistency and distribution of these materials will be very even. But some bluebirds will have a mixture. For example, a nest may be composed of both pine needles and grass clippings.

Things you usually won’t see in a bluebird nest:

• trash
• fur
• leaves (lots of leaves)
• feathers
• moss
• sticks
• wood chips

It is possible that a few scraps of the above might end up in a bluebird nest. But it will not comprise the majority of the material used. At most, you might see one or two random feathers in a nest cup. Or a random string. You also won’t likely see a combination of two or more of these items. For instance, in a bluebird nest, you likely would not see a combination of trash and feathers.

The one time, you might find moss or sticks in the nest box is if your bluebird built her nest on top of an older nest. In this case, you’ll see a layer of some other material followed by a top layer of pine/straw/grass.

What you won’t find in a bluebird nest is several feathers, or several bits of string. If you see a lot of any of those other items, a different bird is very likely using the nest box.

House sparrow nests usually have a wide mix of different types of material. While you might still see a lot of tall grass in a house sparrow nest, you may also find several feathers, leaves, old plastic, paper, sticks and even trash.

In fact, the presence of several pieces of litter/trash in a nest is a very very good signal that this is a house sparrow nest.

As far as things you won’t see in a house sparrow nest – that’s very unclear. House sparrows are not at all picky about what they choose. And they will build their nest out of whatever random stuff they find.

Bluebird nest vs. house sparrow nest: Nest height

When opening a nest box and discovering a complete nest, a typical distinguishing factor to help you tell a house sparrow nest from a bluebird nest is nest height.

House sparrows nesting in nest boxes generally fill the nest box all the way to the ceiling, while bluebirds will fill the box to just below the entry hole.

There are caveats to nest height as a distinguishing factor between house sparrow nests and bluebird nests:

Some bluebirds have been observed filling the box with material right up to the entry hole, sometimes even coming up to the entry hole’s halfway point.

While bluebirds are pretty loyal when it comes to nest shape and material, each bird can be different when it comes to nest height. Some may build very shallow nests, while others have very tall nests.

Likewise, house sparrows very typically fill an entire box, but you will sometimes discover exceptions to the rule.

Bluebird nest vs. house sparrow nest: Egg color

If there are eggs in the nest, the color and size of the eggs can help you determine whether a nest belongs to a bluebird or a house sparrow.

The majority of all bluebird eggs are blue. However, some bluebirds are known to lay white eggs.

But a very important distinguishing characteristic between bluebird eggs (whether blue or white) and house sparrow eggs is the presence of speckles on grayish colored eggs. If you see dark speckles on a grayish brown egg, you do not have bluebird eggs.

Speckled grayish eggs do not necessarily mean you have house sparrow eggs. Chickadees eggs also have speckles – though they’re lighter brown, the speckles are smaller in size, and the base egg color is white.

Cowbirds, which are North American birds that lay eggs in other birds’ nests also have speckled eggs with a grayer base color. However, cowbird eggs will be larger, and you should only see one or two at most in a nest box (usually with a bluebird egg). Do not remove cowbird eggs. They are protected birds in most states.

So when observing eggs, and you find speckled eggs, you will want to use your other clues to determine whether the bird that laid them was a house sparrow and not another native cavity bird.

How to tell the difference when it’s hard to tell the difference between a house sparrow and bluebird nest

There are a several situations that will make it hard to figure out if you have a bluebird nest or a house sparrow nest in your nest box. Some examples of when you’ll encounter these challenges are:

• When nests are still under construction
• When house sparrows have built a nest on top of an existing bluebird nest
• When you simply have a messy bluebird
• When the nest you have is not a bluebird nest or a house sparrow nest

Don’t worry, we still have tips on how to navigate these situations so you can be sure of what you have.

When nests are still under construction:

One of the most challenging times to tell whether you have a bluebird nest or a house sparrow nest in your nest box is when the nest is still under construction.

During the construction period, you may not see a defined cup, and the nest may look a little messy, which might make you think you have a house sparrow nest, but that might not be the case when a nest is in its infancy.

The best way to figure out if you have a house sparrow nest or a bluebird nest, or even something else, is to watch your nest box. Usually half an hour to an hour is all the time you’ll need to observe what kind of bird is carrying stuff into the nest box.

If you are still having trouble identifying house sparrows from other birds, we have a video guide to help you.

Table 1 below has a few quick indicators of what kind of bird you have.

An important note about differentiating house sparrows from other brown birds is that one single characteristic is not enough to properly identify a house sparrow. You need to look for combined characteristics that are associated with house sparrows.

However, with similar looking brown birds, there are single characteristics that can absolutely rule it out as a house sparrow.

For instance, if the bird you’re looking at has a speckled chest, it is not a house sparrow. If the bird you’re looking at has a very narrow, needle looking beak, it is not a house sparrow. If the bird you’re looking at has a chestnut cap (reddish brown rather than a dull brown), it is not a house sparrow.

Table 1. Defining characteristics to distinguish house sparrows and bluebirds from other birds

When house sparrows build nests on top of other bird nests:

Another challenge when differentiating nests is that house sparrows have been known to build nests on top of other bird nests.

In this situation, you might see the beginnings of a bluebird nest where there is a layer of pine. But higher up, you’ll see straw, trash, feathers and other random materials. In this case a house sparrow has definitely taken over the nest box.

House sparrows are not the only birds that will build on top of old bird nests. House wrens (native to North America) are another example.

So when you see what might be another nest on top of a bluebird nest, examine the materials used.

• Composition all sticks: House wren
• Composition inconsistent, fills the entire box: Likely house sparrow
• Composition moss and fur: Chickadee or titmouse

This is not an exhaustive list, but it is a good start to help you determine what bird built on top of a bluebird nest.

When you simply have a messy bluebird

House sparrows are notorious for building messy nests with material that hangs out of the entry hole. But some bluebirds can be pretty messy too, and this can make it really hard to trust whether you have a house sparrow nest or a bluebird nest.

So here is what to do in this situation:

• If the nest is just messy but made of consistent material, observe it until you see what type of bird is going into the nest box.
• If the nest is messy and has trash, feathers and other inconsistent material that fills the box completely, you’ve got a house sparrow.
• When in doubt, always observe what bird is entering the nest box.

When the nest you have is not a bluebird nest or a house sparrow nest

The last scenario that can make nest identification is hard is when the nest you’re looking at doesn’t seem to meet the criteria we’ve just discussed.

For example:

• Nests made entirely of twigs and sticks that fill the nest box – House wren
• Nests made of moss and wood chips, and lined with fur – Chickadee or titmouse
• Nests made of inconsistent material, lined with feathers and has a neat cup – Crested flycatcher
• Nests made of somewhat inconsistent material with a neat cup – Nuthatch
• Nest made of grass and a neat cup and lined with feathers – Tree swallow
• Nest made of sticks with a neat cup and lined with leaves – Purple martin

Why differentiating between bluebird and house sparrow nests is important

Just in case you’re not sure why it is so important to find out whether you have a bluebird nest vs. a house sparrow nest, we’re going to dive right into that question.

House sparrows are not only an introduced species in North America, they are an invasive species. This means they cause ecological harm. Not only do they outcompete native birds for resources like food and shelter, house sparrows are famous for killing native cavity nesting birds.

In fact, house sparrows are one of the biggest reasons purple martins are almost completely dependent on human management to nest.

If you are certain you have a house sparrow nest in your nest box, it is very important you remove it.

Is it legal to remove house sparrow nests and eggs?

Because house sparrows are an invasive species, it is legal in most states and cities to remove active house sparrow nests, eggs and even chicks.

In fact, it is also legal to trap and humanely euthanize adult house sparrows for this same reason, but we won’t go any further into that topic in this article.

When removing house sparrow nests, be sure to use gloves. You may even want to wear a mask because house sparrows are colony birds and carry a lot of bacteria, fungi and viruses that can be hazardous to your health. You will also want to wash your hands thoroughly even if you wore gloves.

For eggs, you can completely remove them, or you can addle them (oil them) and put them back in the nest. Addling will ensure the eggs won’t hatch, and the mother house sparrow won’t try to lay another brood.

This information may make your heart sink a little. And we understand that. If conservation and wildlife management were easy, we wouldn’t have the ecological troubles we have now. Loving your backyard birds and being a good landlord with a heart for conservation takes a lot of sacrifice.

Nest box monitoring to identify nests

This article has talked a lot about characteristics that differentiate bluebird nests from house sparrow nests. But all of these characteristics require you to go up to the nest box, open it up and check.

You might be wondering, is it ok to do that? Or how do you do that without scaring your bird off? Or, what if you scare your birds off for good? Will opening the box harm the eggs? Will it scare the nestlings?

These are all important questions to ask, and the good news is not only can you open the box up to take a look, it is absolutely encouraged.

Furthermore, it takes a lot to scare a bird away from its nest for good. When a bird finds a good nesting spot.

We do have a great resource about nest box monitoring. This article explains how to monitor your nest box in ethical ways that won’t cause harm to your birds.

With so much technology, there are even better ways of nest box monitoring aside from manually opening the nest box and checking on it.

Nest box cameras and cell phones allow you to minimize disturbances to the box while still getting amazing information and observations.

During your first year or two with bluebirds, you’re going to have a lot of questions, including whether or not you actually have a bluebird nest. As you get more and more invested in bluebirds and other cavity birds, we encourage you to keep learning and expanding your knowledge. And don’t stop spreading your love and passion for these adorable little birds.