Most people living in North America have become pretty familiar with the house sparrow. These are invasive, nonnative the little brown birds that especially love to hang out in commercial areas like building signs, parking lot trees and fast food joints. They also love backyard feeders and birdhouses.
But there is another nonnative sparrow in North America that is less familiar to us. This is the Eurasian tree sparrow, a cousin of the invasive and highly aggressive house sparrow.
Based on observations, Eurasian tree sparrows can also be aggressive toward native North American cavity nesting birds. They are not quite as aggressive as house sparrows, but we have certainly observed nest box attacks and nesting evictions.
UPDATE: We now have video documenting a Eurasian tree sparrow attacking a female bluebird in a nest box. The attack is very difficult to watch. Much like a house sparrow, the Eurasian tree sparrow pins the bluebird down, pecks and bites her. The bluebird was able to get free.
This video is now really important because many have long wondered if a Eurasian tree sparrow, being smaller, would attack a larger bird – and it will.
Aside from this video, we’ve discovered deceased female bluebird in another nest box during winter break. During this time, Eurasian tree sparrows were the only other bird observed going into the box to investigate. Though we do not have video evidence, we are convinced a Eurasian tree sparrow was responsible for this death as well based on the fact that they had frequented the box. NOTE: because it was winter break, the monitor was out of town, but was less worried due to birds being seemingly less territorial in the winter
Video: [GRAPHIC] Eurasian Tree Sparrow Attacking a Female Bluebird (bluebird escapes)
Video: Differentiating Eurasian Tree Sparrows from House Sparrows
- Video: [GRAPHIC] Eurasian Tree Sparrow Attacking a Female Bluebird (bluebird escapes)
- Video: Differentiating Eurasian Tree Sparrows from House Sparrows
- Eurasian tree sparrows will attack nest boxes and nestlings
- Native adult birds have been observed chasing off Eurasian tree sparrows when outside the nest box
- Adult birds building a nest almost always lose them to Eurasian tree sparrows once they become interested in the nest
- Bluebirds and larger birds are susceptible to attacks
- Minimizing Eurasian tree sparrow attacks with wren guards
- Eurasian tree sparrows fit in a 1-⅛ inch entry hole size
- Eurasian tree sparrows aren’t picky about food when desperate
- Eurasian tree sparrows may be more passive at feeders
- Eurasian tree sparrows do not care for commercial/urban settings
- Old world sparrows are not protected by the MBTA
There is very limited literature about Eurasian tree sparrows in North America because their range has stayed fairly isolated to the St. Louis area for more than a century now.
This isolation limits available observations, all of which we’ve found cite that Eurasian tree sparrows are not aggressive by comparison to its cousin.
However, being based just outside of St. Louis, Nest Hollow’s citizen labs have been able to observe Eurasian tree sparrow behavior with respect to native birds. And in this article, we’ll detail everything we know so far.
Eurasian tree sparrows will attack nest boxes and nestlings
On multiple occasions, we have witnessed Eurasian tree sparrows try to take over an occupied nest. Mainly, these nest boxes were inhabited by smaller birds like house wrens and chickadees. However, unattended bluebird nests with nestlings have been harassed.
Typically, these observations were seen either before a wren guard was put on a nest box or after it was removed from a nest box when nestlings were old enough to evade a wren attack but too young to fledge.
On one occasion, an attack led to premature fledging of a chickadee. We were alerted to the attack after noticing one of the parent chickadees was doing the snake dance outside the box. This is where they fan out their wing and tail feathers and move in a snake-like manner.
On a happy note, the nestling was put safely back in its nest.
Native adult birds have been observed chasing off Eurasian tree sparrows when outside the nest box
Though Eurasian tree sparrows do reside in our range, our observations are still limited. And our trail monitors do what they can to minimize sparrow attacks in the first place. One of the biggest things we want to avoid is the death of adult birds.
Unfortunately, the house sparrow is infamous for killing brooding mothers in the nest box.
We have observed this behavior with Eurasian tree sparrows. On one occasion, our cameras picked up Eurasian tree sparrows investigating a bluebird nest box during the winter time. Around the same time, bluebirds were also investigating. And unfortunately we saw a dead, wounded female bluebird in the box.
The second occasion, we have video footage of a Eurasian tree sparrow attacking a female bluebird. The video is posted earlier in this article, and it is very distressing to watch.
Please keep in mind that Eurasian tree sparrow observations are still highly limited.
Adult birds building a nest almost always lose them to Eurasian tree sparrows once they become interested in the nest
Just like the house sparrow, Eurasian tree sparrows build nests quickly and are able to usurp nests easily.
In every instance where a smaller native adult bird begins building a nest, and a Eurasian tree sparrow discovers it, the Eurasian tree sparrow will take over the nest.
One of our nest box cameras caught a Eurasian tree sparrow hiding in a wren nest, and took the wren by surprise.
Ultimately, the Eurasian tree sparrow evicted the wren and attempted nesting over its nest. Each time we evicted the Eurasian tree sparrow (non-native sparrows are not federally protected, therefore nest interference is legal. And this would not be an active nest), the cycle would continue. First, the house wren would build, only for the Eurasian tree sparrow to take over.
This is not the first occasion. A local park we work with is overrun with house sparrows and Eurasian tree sparrows. In every instance, nest boxes were taken over by either sparrow species.
Bluebirds and larger birds are susceptible to attacks
As we continue to observe the behaviors of Eurasian tree sparrows, we will continue to update this page.
Originally, we were under the impression that Eurasian tree sparrows were not as much of a threat to larger cavity birds like bluebirds. But now we have record that shows otherwise.
One of the things we have recently observed is that bluebirds will go after a Eurasian tree sparrow.
But, we see this also with house sparrows. Outside of the nest box bluebirds and other cavity nesting birds are able to defend their nest and live.
Once inside the nest box, it’s a different story. Even a small Eurasian tree sparrow is able to pin down an adult bluebird (larger than Eurasian tree sparrows) and attack.
Before witnessing this attack, we have observed Eurasian tree sparrows harass bluebird nests, nestlings and eggs, so there is always risk.
You might wonder if Eurasian tree sparrows are as deadly to adult bluebirds and tree swallows as the house sparrow if a bluebird is caught inside its nest box. Originally, when making this article we could not conclusively report one way or another. But we are updating this article as new observations come in.
That said, you probably can tell by now that, yes, Eurasian tree sparrows can be as deadly. While the one in our video above escaped, we did find another dead female bluebird that died from a Eurasian tree sparrow attack (we’re 90% sure it was a Eurasian tree sparrow that attacked since that was the only other bird seen at the nest box).
Minimizing Eurasian tree sparrow attacks with wren guards
Wren guards are little hoods placed over a nest box to hide the entry hole from other birds.
House wrens (native to North America and federally protected), in particular, are known to evict other cavity nesters, poke out and discard eggs and throw very young nestlings out of the nest box.
Afterward, house wrens take over the nest box, sometimes only making a dummy nest.
To prevent eviction, trail monitors and bird landlords will put a wren guard on the nest box after the first egg is laid. This hides the access as well as making too much of an obstacle for uncommitted birds. But parents, who are committed, will still work to access the nest box.
They are not 100% effective, especially if a house wren has already discovered the nest box and is bonded to it.
But what we have also found is that wren guards seem to minimize Eurasian tree sparrow attacks.
The obstacle is too much for them, and the guard typically buys some time for parents to return to the nest box and chase them away.
For Eurasian tree sparrows, this has been pretty effective in our experience. Once again, this is not 100% effective, and it’s possible a sparrow will get past the obstacle and take over the nest.
Eurasian tree sparrows fit in a 1-⅛ inch entry hole size
When protecting chickadees from house sparrow attacks, one of the simplest ways is size exclusion.
House sparrows are larger than chickadees and require an entry hole to be at least 1-¼ inches. Chickadees and house wrens, on the other hand, can get into a smaller hole (1-⅛ inches).
Unfortunately, Eurasian tree sparrows are just a tiny bit smaller than house sparrows, and can fit in the smaller hole size as well.
Therefore, a 1-⅛ inch hole reducer will not protect your chickadees and house wrens.
For house wrens, we have reduced the hole size to 1 inch, with success. The same can sometimes work for Carolina chickadees, but it can be too much of a reduction for black-capped chickadees.
In this case, we would also recommend using sparrow spookers and wren guards as an added measure of protection.
Eurasian tree sparrows aren’t picky about food when desperate
When trying to deter house sparrows from your yard, one of the first and greatest tips is not to put out songbird seed mixes with filler seed.
Filler seed is usually millet, milo and cracked corn. House sparrows and Eurasian tree sparrows particularly love this type of seed because it’s easier for them to eat. They’re not as adept to cracking upon tougher shells like black oil sunflower.
However, what we’ve is that they aren’t picky when times get tough. Particularly come late fall and winter when other food becomes scarce, they will flock to feeders and eat whatever they contain.
Don’t think your nyjer filled finch feeder is safe, or the safflower for chickadees. Eurasian tree sparrows and house sparrows will cling to these feeders and feast.
Unfortunately, we don’t have a good way of getting around this. However, one option is to use put out suet during winter time, and experiment with an upside down suet feeder. These feeder types are good for clinger birds like chickadees, woodpeckers, nuthatches and titmice. But they tend to cause a lot of obstacles for starlings, and would likely be tougher for nonnative sparrows to use.
Eurasian tree sparrows may be more passive at feeders
Compared to the house sparrow, a few avid birders in our network who live in the region of the United States where Eurasian tree sparrows live have reported them to be less aggressive at bird feeders.
In our own observations, we have found this to usually be the case. Certainly, they will hoard platform feeders of all kinds, including suet feeders. They’ll also cling to nyjer feeders, but if there is room, they tend to let other birds eat.
Eurasian tree sparrows do not care for commercial/urban settings
The limited articles out there regarding Eurasian tree sparrows mention the fact that house sparrows outcompete these birds.
The primary reason cited is that house sparrows are slightly larger and more aggressive.
Already, we’ve somewhat debunked the aggression situation. While Eurasian tree sparrows may not be quite as persistent and viscous as a house sparrow, they are a close second.
Instead, our hypothesis regarding the spread and natural success of the house sparrow over the Eurasian tree sparrow has to do with commercial preference.
House sparrows have become commonplace in North America, and one of the reasons is because they are so content to make their homes in commercial and urban settings.
You will find them nesting in signs, roosting in the trees of parking lots, begging for food at an outdoor eatery, and camping in pallets at hardware stores and garden centers.
This flexibility for commercial settings may have been one of the bigger contributing factors to their success, as natural habitat loss is not as devastating for the house sparrow.
From our years of general observation of the Eurasian tree sparrow, we have discovered they would rather stay away from urban locations, preferring residential locations, countrysides and parks.
When out in commercial places that have house sparrows, we have actively looked for Eurasian tree sparrows to be in the mix, but have not yet found this.
We have observed mixed house sparrow/Eurasian tree sparrow colonies in parks and in overrun purple martin houses.
Therefore, we believe that one of the bigger reasons the Eurasian tree sparrow has not spread as rapidly as the house sparrow is their aversion to urban places.
Old world sparrows are not protected by the MBTA
So with the Eurasian tree sparrow being found to be more aggressive than once believed, as well as being nonnative, the question is – are they protected?
Federally, the Migratory Bird Treaty Act (MBTA) does not protect any old world sparrow, which would include house sparrows and Eurasian tree sparrows.
Old World sparrows mean sparrows native to Europe and Asia (Eurasia), rather than the New World native North America (and really South America – but we’re only discussing NA).
Old world sparrows are referenced on a list for which the Migratory Bird Treaty Act does not apply.
Despite federal rules, state and city statutes and ordinances might differ. For instance, in Illinois, the Eurasian tree sparrow is protected. In many other states, it is not.
When considering trapping and dispatching, we recommend contacting your state’s conservation department to find out the rules.
As of right now, these are the observations we’ve had, and we will continue to stay observant and document other behavioral facts we witness as time goes on.
