Where have all the tree swallows gone this year? That’s the question I recently received from a couple of readers concerned about the absence of tree swallows using their backyard bird houses. Indeed, according to my friends, the tree swallows did not return to use the nest boxes after a 20-year run of annual use. Baffling, to say the least.

    Where have all the tree swallows gone this year?  That’s the question I recently received from a couple of readers concerned about the absence of tree swallows using their backyard bird houses. Indeed, according to my friends, the tree swallows did not return to use the nest boxes after a 20-year run of annual use.  Baffling, to say the least.   

    I wrote that I observed basically the same thing where I live this season—lots of empty nest boxes and not many tree swallows. Even the eastern bluebirds are fewer in number this spring and summer.   

    The weather had an impact on songbird production this breeding and nesting season, especially for birds such as tree swallows and bluebirds that depend almost exclusively on a steady diet of insects. And given the late arrival of spring this year, insects were hard to come by.  Such conditions aren’t favorable to insectivorous birds and, as such, birds like tree swallows likely opted to migrate to areas where insects could be found more readily.   

    Even so, just as soon as our springtime weather finally warmed enough to where insects became fairly abundant once again, several species of swallows do begin showing up throughout Minnesota.  In all, six of the nine North American species of swallows migrate to Minnesota to breed and nest.  All of them share similar physical characteristics with one another, but each is quite unique in their own right.   

    Topping the popularity list of Minnesota swallows is the largest of the swallow clan, in addition to the only species of swallow not to have “swallow” as part of their name.  The purple martin is that condo-loving, social butterfly of the swallow world.  Here’s a swallow that has come to rely almost exclusively, interestingly enough, on man-made bird houses for nesting.     

    Like several other swallow relatives, purple martins are cavity nesters; specifically, they evolved to nest inside holes in trees.  But perhaps do in part by loss of their preferred nesting habitat (larger trees with suitable tree cavities), these colonial nesting birds somehow adapted to nesting in bird houses.   
Evidently, purple martins east of the Rocky Mountains rely almost entirely on “human supplied housing”, whereas those birds nesting west of the Rockies typically nest in their ancestral ways—that is, inside of tree cavities.   

    Two other species of swallows occurring in Minnesota each year are referred to as “brown” swallows: the northern rough-winged swallow and the bank swallow.  Honestly, I’m not certain if I’ve ever observed the rough-winged swallow, but I’m quite familiar with bank swallows.   

    Having spent countless hours canoeing the Crow Wing River that meanders through Hubbard and Wadena counties, bank swallows are regular sights along the sandy, high banks commonly encountered alongside the river.    

    Both species nest in holes they excavate themselves in sandbanks.  Obviously, the sand of choice has to be of the right consistency, otherwise their burrows would collapse.  Bank swallows, the more sociable of the two “sandbank swallows”, are colonial nesters, whereas northern rough-winged swallows nest singly.     

    Having observed the former species along the banks of the Crow Wing many times, it’s a pleasant experience to watch bank swallows capture insects above the surface of the flowing river.  Mesmerizing to see as tens of dozens swoop and dart in their haste for food, they just as quickly return to their sandbank cavities to feed hungry nestlings.
Another common swallow that nests in Minnesota each season, frequently near water and often underneath bridges, inside large culverts, or beneath the eaves of buildings, is the attractive cliff swallow.  Here’s a species of swallow that builds perhaps the most unique of the nest-building swallows.     

    Shaped like gourds, cliff swallow nests are constructed entirely out of mud pellets comprised of sand, silt and clay.  From 1,000 to 1,400 mud pellets (which also represents that many mouthfuls of mud and trips to the nest!) and 1 to 2 weeks is required to complete the construction of each individual nest.   

    The last two swallows occurring in Minnesota are my favorite swallows.  I am forever grateful that, because of their abundance and eagerness to utilize bird houses, the ubiquitous and cheery tree swallow has helped fill the numerous vacancies that most of my “bluebird” houses generally provide.    

    Tree swallows are stocky, broad-winged swallows with very white breasts, giving them an almost penguin-like appearance when perched with folded wings.  Widespread amongst all swallows, tree swallows, like purple martins, choose tree cavities and bird houses for nesting and raising offspring.     

    As swallows go, tree swallows are aggressive, especially the males when defending their nesting territory.  The species’ assertiveness is undoubtedly a primary reason why tree swallows are known to out-compete eastern bluebirds for suitable tree cavities and birdhouses.

    Therefore, in recognition of this trait, it is advisable to erect pairs of bluebird houses at a distance of no more than 10 to 20 feet apart, or back-to-back on the same post.  Thus, since tree swallows don’t allow other tree swallows to nest within 20 feet, the other nearby birdhouse is free for a nesting pair of bluebirds to use.    

    And lastly, as already mentioned, is the sweet and beautiful barn swallow that I came to know so well as a young boy on the farm.  This orange-breasted swallow with the deeply forked tail, is an elegant looking, easy flying swallow that, to me, exemplifies grace on wing.  
Constructing its half-cup nest of mud and organic materials underneath the eaves of buildings or onto rafters or floor joists inside of buildings, the tolerant barn swallow seems unaffected by human activity.     

    Swallows, all of them, birds designed for capturing flying insects while they themselves careen through the air with no apparent effort, are birds to marvel at as we get out and enjoy the great outdoors.