Tree Swallows

Bird Bros. - Home Builders for Birds

For over a quarter of a century, bluebirds and tree swallows have come to Bingham Brook Farm to raise their broods. It wasn't until a large portion of the woodlands were cleared that these birds - and many other field birds - started to appear. While bluebird boxes have been part of the farm landscape for decades, it wasn't until 2011 that we decided to research the tree swallows that inhabited the majority of the bluebird boxes and performed such beautiful acrobatic displays in the morning and evening. I believe what we have learned about tree swallows and bluebirds, both from over three decades of firsthand observation in the field and from published research will surprise you, but more importantly hopefully alarm you to what is happening to these wonderful acrobatic creatures under the misguided - and ornithologically erroneous - initiative to save bluebirds.

Enormous thanks to Chris Gates who manages the Salmon Creek Tree Swallow Project in Hilton, NY for the massive amount of information and documented research. His work and information is the basis for Bingham Brook Farm's revised tree Swallow project and their website has been the primary source for a preponderance of the following information.

If you are interested in supporting tree swallows, we urge you to visit the Salmon Creek Tree Swallow Project -

The Bird Brothers are Chris P. Janelli and master woodcraftsman Peter L. Becket.

Bluebirds are beautiful, but this is about the acrobatic tree swallow; one of the friendliest birds around human habitations. They subsist primarily on a diet of insects catching upwards of a thousand a day, and sometimes supplemented with small quantities of fruit. They are excellent fliers and acrobatically catch insects in mid-air in their bills. During early mornings and evenings dozens of these aerial bugsters can be observed winging, swirling and swooping against the sky in an air show reminiscent of WW I dog fights.

The Tree Swallow, Tachycineta bicolor, is a migratory passerine bird that breeds in North America and winters in Mexico, Central America and the Caribbean

Passerine -

When not breeding and defending its territory, tree swallows form flocks of several thousand birds near roost sites. While Bingham Brook Farm is situated in the Berkshire Mountains in the NW corner of the state where the CT-NY-MA borders meet, which is about as far from Long Island Sound as one can drive in CT, our seasonal tree swallow visitors are very likely participants in one of nature's greatest phenomena - The Massing Of The Swallows On Goose Island, a small island in the Connecticut River.

"There, for perhaps a half hour, they mill around in an enormous, undulating mass of life, specks of black in the fading late-day light. Then, apparently following the lead of one or more birds, they coalesce into a funnel form, as if a tornado, and spiral down by the thousands into the reeds of Goose Island off the Old Lyme shore. Within a minute or two as many as 500,000 swallows disappear into the reeds, their bed for the night. It is one of Connecticut's most spectacular natural phenomena, a kind of first stage in the fall swallow migration, lasting only a matter of weeks each year, and, in all of the state, confined to just that one spot, one that is not easy to access without a boat. Discovered only in the late 20th century, the massing of the swallows above Goose Island is now celebrated as another of nature's awe-inspiring rhythms, like the migration of Arctic caribou or the return of salmon from the sea to spawn in rivers."

Read the complete Hartford Courant article - The Massing of the Swallows on Goose Island

Exactly what is the tree swallow - bluebird "problem"?

There are three species of bluebirds, the Eastern, Mountain, and Western. Like tree swallows, bluebirds depend on cavities for nesting but are unable to make their own, so tree swallows and bluebirds compete for nest boxes. This means that where their ranges overlap tree swallows will compete with bluebirds for any available cavities, something they were doing long before humans ever came on the scene. Every bluebird box erected by a human is subject to that age-old competition.

For many decades, there has been a popular and active movement across the US to erect bluebird nest boxes. Today, there are many people devoted to "bringing the bluebird back" to former levels of abundance, an impossible task, based on misconceptions and myths, as is explained later on. Because of this "to bring them back" misconception, some bluebird lovers become annoyed when their boxes are occupied by other species, especially tree swallows. Many bluebird enthusiasts believe that tree swallows take all of the nesting boxes thus driving their bluebirds away. NOTHING COULD BE FURTHER FROM THE TRUTH.

The fact is, with the exception of their wing length tree swallows are significantly smaller than bluebirds in every external body dimension and are typically outweighed by bluebirds 30 grams to 20 grams. Chris Gates' observations at the Salmon Creek Tree Swallow Project confirm that if a bluebird really wants a nesting box they are very capable of taking and defending it from at tree swallow. But when it comes to something bigger - like a human being - the tree swallow is at a serious - too often deadly - disadvantage.

Unfortunately, some bluebird lovers, especially in the Eastern Bluebird range, strongly believe that encouraging tree swallows is out-and-out wrong. In some instances, resentment is so strong that when tree swallows occupy a bluebird box, an ignorant minority of bluebird hobbyists feel justified to destroy any tree swallow nests and eggs they discover in their boxes. This is both tragic and unnecessary, to say nothing of immoral and illegal. The truth is there are accepted bluebird management techniques that can reduce most strife between the two species. AND THEREIN LIES THE BASIS OF THIS STORY.

Bluebirds and tree swallows are both native songbirds, equally worthy of care, consideration, and conservation, and when people understand the real story about tree swallows and bluebirds, they often come to realize that one species is not more "desirable" than the other. In fact, TREE SWALLOWS AND BLUEBIRDS MAKE THE BEST OF NEIGHBORS!

Before we get into the solution to having both bluebirds and tree swallows living in harmony so that you can enjoy both species, let's get some history and facts straight.

Bluebirds are NOT in trouble and don't deserve special treatment!

Despite what you may have heard or read, there is nothing unique or inherent about bluebirds that warrants special treatment or favoritism, and certainly not at the expense of other native species. Contrary to popular belief, not one of the three bluebird species is endangered or threatened today and none has been at any time in its recent history! No bluebird species is in peril, needing to be rescued. In 2008, the International Union for Conservation of Nature and Natural Resources rated all three bluebirds as species of "Least Concern!"

In 2004, Partners in Flight's authoritative North American Landbird Conservation Plan estimated there were 10,000,000 Eastern Bluebirds, 5,200,000 Mountain Bluebirds and 1,400,000 Western Bluebirds for a total of 16,600,000 bluebirds. In comparison, nationwide there were an estimated 20,000,000 tree swallows.

So why all the fuss over the bluebird - particularly the Eastern Bluebird?

The Eastern Bluebird population of the 19th and 20th centuries did indeed fall, which caused concern. But this fall must be put into proper historical - and environmental - perspective.

"Before its dramatic alteration by humans, most of North America east of the Great Plains was dense forest. Since Eastern Bluebirds prefer open and semi-open areas with scattered woody vegetation, they were probably restricted to areas burned over by forest fires and in early stages of regeneration. Burns would have dead trees with cavities, perches for hawking down on insects, and fruit-bearing shrubs typical of early plant succession. However, as burns returned to forest, bluebirds would have needed to relocate. In any given year most of the eastern forest would have been unsuitable habitat for them. Therefore, under natural, pre-human conditions

Eastern Bluebirds were never likely to have been common breeding birds except perhaps locally on old burns, and they were certainly never the abundant species that folklore and some popular literature would have you believe.

Then, Native Americans arrived. Their clearings for farms and villages increased bluebird habitat. Fires they set to create and maintain feeding openings for deer, elk, and bison would also have benefited Bluebirds. But it was when North America was colonized by Europeans that the forests began to be cleared in earnest. By the mid 1800s the eastern forests were almost gone, replaced by small farms with cropland, pastures and orchards. It's hard to appreciate how completely deforested the land was unless you see photos from the time. Though this was devastating for woodland wildlife, it was a bonanza for bluebirds! The small farms of 19th century rural North America offered absolutely perfect habitat, and bluebird numbers skyrocketed."

Bingham Brook Farm Note: Nowhere was this effect of human interaction with the environment more evident than here at Bingham Brook Farm situated at 1,100 feet on the slope of the Mt. Riga Plateau. At the turn of the 19th century, the Plateau as well as much of the land within Salisbury had essentially been denuded of its trees that were converted into the charcoal used in the local iron furnaces. With the exception (on Bingham Brook Farm) of some giant white oaks left standing, the Plateau's forest is secondary growth with the majority of trees less than 100 years old.

"But then things changed again. In 1851 House Sparrows were introduced from Europe, followed in 1890 by European Starlings. As these aggressive cavity nesters spread they out-competed bluebirds for many nest sites. The small farm, once so inviting, also changed. Marginal, unprofitable farms were abandoned and began the slow but inevitable return to forest. On better farms mechanized equipment replaced horses and mules, and allowed small fields to be combined into large. Automobiles meant pasturage was not needed for horse-drawn vehicles. "Clean orchards" and dwarf varieties of fruit trees became the rule. Suitable cavities and habitat for Bluebirds became scarce. Then in the 1900s indiscriminate application of chemical pesticides became common, poisoning Bluebird food. Bluebird numbers plummeted. Luckily, by the 1930s and 1940s observant people began to realize how scarce they had become relative to the golden days of the 1800s, and started the movement to "bring back the bluebirds".

Since then, bluebird nest box programs have been very successful and suburban backyards, parks, and cemeteries are now commonly utilized for bluebird habitat. More responsible use of pesticides has certainly helped. And although it can't be proven, competition with House Sparrows and Starlings may have selected for bluebirds that are genetically rougher and tougher. Let's hope it's true. Whatever the reasons, Eastern Bluebirds are now common nesters again across much of eastern and central North America. It's very possible Eastern Bluebirds are more abundant now than when the first humans arrived!

However, to expect bluebird numbers can (or should) ever return to the highs of the 1800s is extremely unrealistic. House Sparrows and Starlings are here to stay. Forests have returned in many places, although a mere shadow of their former size. And the small farm of yesteryear will not return. A few hundred million more people with houses, cars, highways, and buildings now occupy bluebird habitat of the 1800s. The clock cannot be turned back. The Eastern Bluebird cannot re-attain the abnormally high numbers of the 1800s. Those levels are gone forever because the conditions that allowed them are gone forever.

These concerns are mostly based on unrealistic hopes and expectations that a restoration to the bluebird population levels of the 1800s is possible, and that the bluebird needs to be "saved". Actually, far from being a species in peril Eastern Bluebirds are doing extremely well today compared to most birds, aided by their toughness as a species, their devoted followers, some new habitat, and the growing popularity of winter feeding. Bluebirds are among the lucky few bird species whose future seems assured. Bluebird hobbyists must recognize that bluebirds never were and never are going to become truly abundant, and that having bluebird boxes occupied by tree swallows or other native species does not in any way jeopardize bluebirds' existence. Rather, it's our own species' activities, for better or worse, that will determine the population swings of bluebirds, swallows, and most other species on earth, at least in the short run."

The Solution to the so-called problem is really about spacing!

Here is the simple answer to the problem. Bluebirds will defend a 300-foot territory against any other bluebird. Tree swallows will defend a 100-foot territory from any other tree swallow. But while tree swallows and bluebirds might fight over a nesting box, they will literally cohabitate peacefully side by side as this photo shows!

Spacing nest boxes for bluebirds is critical. Most of the competition between tree swallows and bluebirds would be eliminated if bluebird hobbyists simply followed box spacing guidelines. Since bluebirds defend large feeding territories around their nests, they don't want to nest close to other bluebirds. Experts recommend that bluebird boxes be spaced at least 300' apart (the length of a football field!), preferably even more.

In contrast, tree swallows only defend a small area around their nest and, unlike bluebirds, tree swallows usually leave their defended area to feed. The recommended spacing for tree swallow boxes is only 100' apart. This means many pairs of tree swallows can potentially nest within an area that just one pair of bluebirds would claim.

When bluebird boxes are spaced far enough apart the way they should be, a pair of bluebirds usually contends with just one pair of tree swallows, and in these contests the larger, stronger bluebirds normally win.

It's a myth that bluebirds are "gentler" and "less aggressive" than tree swallows. Bluebirds are very capable of both intense and prolonged aggressive behavior; their behavior patterns just differ from the swallows'. Swallows rely on screaming, persistent approaches, dive-bombing, and pecks given on the fly-by. A bluebird's usual tactic is to wait at the box, making occasional hostile displays such as wing-flicks, and then dashing out to intercept the swallow, grappling with it and tumbling with it to the ground where the bluebird can peck the swallow and strike it with its wings.

One pair of bluebirds is normally more than a match for one pair of tree swallows, but problems can arise when bluebird boxes are spaced closer than 300'. Clusters of boxes in one bluebird territory may attract groups of swallows who can mob a lone pair of bluebirds. However, even then truly fit bluebirds often win out. The proof? Bluebirds commonly secure and defend boxes, and nest successfully within tree swallow grids of 50-100 active nests at ornithology research sites. At the Salmon Creek Tree Swallow Project in Hilton, NY bluebirds have raised broods in three of their five tree swallow projects over the years. Their experience is that if bluebirds really want a box they are very capable of taking and defending it from swallows. To learn more about tree swallow grids, visit the Salmon Creek Tree Swallow Project page on grids -

The Solution: reduce bluebird-swallow competition by pairing boxes. There is no way to design a swallow-proof bluebird box because swallows are so much smaller and slimmer than bluebirds. However, there is one proven technique that allows both songbirds to nest together successfully. This is "pairing"; setting up pairs of boxes with each box of a pair no more than 5-10 feet apart.

Since tree swallows seldom allow another pair of swallows to nest within 20', the second box is free for bluebird use and the two species, after some initial squabbling to sort out who gets which box, can co-exist.

Why do Tree swallows use nest boxes?

Cavity-nesting birds like tree swallows, that can't make their own cavities, usually face a shortage of nest sites. Competition for cavities can be intense, even a matter of life and death, since failing to reproduce is a critical failure for short-lived songbirds. Tree swallows must compete for nest sites with other tree swallows and also with other cavity-nesters like bluebirds, wrens, starlings and house sparrows.

Since natural cavities are scarce tree swallows quickly accept nest boxes, and unlike many other cavity nesting species they aren't picky! They'll use just about any box they can get into. AND HEREIN IS A BIG PROBLEM FOR TREE SWALLOWS.

Many people believe the small bluebird boxes are just fine for tree swallows, especially since tree swallows use them all the time. In fact, for far too long here at Bingham Brook Farm we were guilty of believing bluebird boxes were OK for tree swallows, since year after year they returned and took up residence and raised their young.

Today we know better. Bluebird boxes are NOT OK for tree swallows. Over the course of a quarter of a century the boxes at Bingham Brook Farm have gone from small (1st generation) bluebird size boxes to larger (2nd generation) and then even larger (today's 3rd generation) tree swallow boxes.

1st Generation Box
Interior: 15 sq. in.

2nd Generation Box
Interior: 22.5 sq. in.

3rd and 2nd Generation Boxes
Interior: 35 sq. in. vs. 22.5

In fact, the traditional small size bluebird box should be eliminated and replaced with a bigger tree swallow box - preferably with the Bird Bros Tree Swallow EasySlide Brooder Box.
Here's why:
1. Bluebirds and tree swallows will cohabitate - literally side by side.

2. Tree swallows need bigger boxes - bluebird boxes can kill tree swallow fledglings.

3. Bluebirds will nest in a bigger tree swallow box.

There are many published box plans and boxes sold in stores that are intended for bluebirds, but will eventually - and tragically - be used by tree swallows. While it is true that tree swallows will accept small boxes, their nestlings may not thrive or fledge successfully when confined to a small space. The chief reason is this: bluebirds may be bigger than tree swallows, but the swallows have bigger broods than bluebirds - often as many as 7. Since a large brood of tree swallow nestlings can't spread out in the small internal floor space if a bluebird box, the nestlings are at risk of death from overheating during hot spells. Further, smaller nestlings may get trampled by their larger siblings, have their feathers soiled with feces, and be unable to reach food brought by parents.

Tree swallow nestlings also require space to exercise their wings so they can fly strongly when they fledge. It's possible that lack of space may even interfere with proper bone and feather development.

This photo illustrates the small size of two bluebird boxes compared to a larger box that adequately accommodates this brood of 7 tree swallows.


It is recommended that to avoid potential cramping problems that nesting boxes have a minimum floor size of 5 X 5.

Even that size appears to be too small for these 7 nestlings.

In recent years, some bluebird hobbyists have advocated using very small boxes in a well-intended but futile attempt to prevent box use by House Sparrows.

PLEASE - DON'T USE SMALL BLUEBIRD BOXES as they often have interior dimensions that are far too small for swallow broods. Most naturalists today believe bluebird boxes are totally unacceptable in a tree swallow project.

The opinion of Chris Gates who manages the Salmon Creek Tree Swallow Project is that "the North American Bluebird Society and any of its member clubs and individuals that continue to promote the use of boxes with small interiors show a blatant disregard for the lives of other native songbirds."

For over two decades at Bingham Brook Farm we have used larger boxes - not because we knew better, but fortuitously because of the standard size rough cut native lumber we use to make our boxes.

So now that you know that bluebirds and tree swallows will nest side by side, that they require different territorial spacing between nest boxes that they will nest in the same size box, and that putting up small bluebird boxes are potentially setting "miserable little death traps" for tree swallows, WHY WOULD YOU PUT UP A BLUEBIRD BOX?

Today Bingham Brook Farm uses the patent applied for Bird Bros Tree Swallow EasySlide Brooder Box (pictured here) that has an interior floor space of 5" X 7" (35 square inches).

Our experience at Bingham Brook Farm is that boxes left out during the winter are typically occupied by mice, squirrels and flying squirrels (we like the flying squirrels).

The Bird Bros Tree Swallow EasySlide Brooder Box incorporates innovative improvements that make them easy to mount and take down, open and close for research and banding birds, clean and disinfect. If they are left out year round the innovative floor system makes them easy to winter rodent proof.

The Bird Bros Tree Swallow EasySlide Brooder Box has been field tested and proven to meet the nesting needs of both bluebirds and tree swallows.

Unless otherwise indicated, the contents of this website are © 2009 Chris P. Janelli
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