Where Have All the Swallows Gone?

Tree Swallow

Barn and Tree Swallows

Gliding, diving, graceful birds

Acrobats in flight.

On a boring day in May, June, or July you can always sit on the porch with a cool drink and watch the swallows.  This year the Tree Swallows won the annual competition for the birdhouse down by the creek, the one with the water view, and the Bluebirds were again relegated to the other two houses along the driveway.  I don’t pick favorites as both have great appeal.  The birdhouse by the water does have some issues as the smart Fish Crows from the neighbor’s trees are always poking their large bills through the hole, trying to snag a hatchling for lunch.  The parents do a brave job driving off the much larger crows, but I fear they are not always successful.  That doesn’t seem to stop the swallows from coming back here year after year.

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Barn Swallow, Hirundo rustic,                   click on any photo to zoom

The entertainment is their airshow.  Swooping, sharp corners, straight up, diving low over the grass and river, catching insects, eating and drinking, even in flight.  In my book only the terns can rival the swallows in aerial acrobatics.  The Tree Swallows arrive first in the spring to stake out a nesting cavity, and stay later in the fall since they are the only swallow that can also feed on berries when the bugs are no longer plentiful.  The later arriving Barn Swallows almost exclusively build their mud nests on man-made structures–in my yard that’s the underside of the boat dock.

Eastern Bluebird

Eastern Bluebird at the “loser’s” house

The “Barnies” are the only North American swallow that has that deeply forked swallow tail.  It, plus the chestnut colored throat make the ID easy.  The Tree Swallows are striking birds with pure white below and metallic blue or green above, depending on the light.  These are the most common swallows in the East, but keep an eye out for the Bank S. with its dark chest band, the less sociable and more bland Northern Rough-winged S., and an occasional Cliff S. with its buff rump and forehead.

Tree Swallows

Tree Swallow flock

Then one evening in late July you notice they’re gone.  No fanfare or goodbyes, just gone, show’s over.  The birdhouse and dock are vacated.  And why did they leave so early?  There are still plenty of bugs, warm weather and sunshine, and maybe even enough time to raise another brood.  But I’ve learned that they are not gone.  The swallows haven’t really left for the season yet, but have changed their venue.  Just travel a few miles east to the inland fields with power lines or the vast tidal marshes along Delaware Bay and you’ll find them again.  You’ll see flocks, sometimes huge mixed flocks of swallows, no longer interested in breeding but now more intent upon consuming large volumes of insects and storing up energy for the coming fall.

Northern Rough-winged Swallow

Northern Rough-winged Swallow, Stelgidopteryx serripennis

The fall migration is a much bigger deal than its spring counterpart.  A successful breeding season will swell the flock many times over the number of birds that arrived the previous spring.  But there’s danger ahead.  Its been reported that the mortality rate for songbirds during the fall migration and at the wintering sites may be as high as 85% due to disease, predators, accidents, weather, etc.

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Tree Swallows, Tachycineta bicolor

 Flocking prior to and during fall migration, and continuing all winter, may in part be a safety mechanism to confuse predators with visual overload.  As opposed to most songbirds the swallows migrate in these large flocks during daylight, perhaps relying on visual clues for guidance.  This also allows them to feed on the fly.  The Tree Swallows will actually undergo a gradual molt during the trip to South Florida, the Gulf coast, Cuba, or Mexico, whereas the “Barnies” wait to molt until they have arrived at the wintering grounds in South America.

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Coastal flock prior to fall migration

So the swallow’s sojourn in their summer breeding grounds appears to be a two part affair.  First mate, nest, and raise the young.  But when that’s accomplished congregate in great numbers, fellowship, teach the juveniles advanced flying skills, and build up fat reserves for migration.  And when the mysterious word is spoken, whether it’s hormonal, sunlight, or temperature, be ready to head south en masse.  Their return in the spring will not be in massive flocks but rather in smaller groups of survivors, coming north to start the cycle all over again.

What’s Up With the Martins?

Purple Martin

Purple Martin, Progne subis

The last of April and early May were remarkable for the cold, wet weather here in Maryland and throughout the Mid-Atlantic.  I heard we had 14 straight days of measurable rain and the thermometer was clearly forgetting that the spring equinox was six weeks ago.  As we pulled into our rural road, returning from a hot supper out, there was a good-sized flock of Purple Martins, maybe 25 or 30, blocking our way.  As I slowed down surprisingly only a few flew away and even those birds quickly landed a short distance further down the road as if to claim it for themselves.  I ran an obstacle course through them trying hard to straddle as many as possible.  What was going on?  These were not the usual energetic, swooping, and vocal swallows one usually sees each spring.  The next morning the martins were still on the road, but now there were several squashed bodies of those that had refused to yield to traffic.  This went on for several days and the body count mounted until the survivors finally disappeared.

Purple Martin

Martin roadblock; note the droopy tail and wings

About this same time I was at a party where friends of mine recounted another episode of strange martin behavior occurring about the same time in the cold and drizzle.  This couple are bird lovers and astute observers of the flora and fauna in their yard. They noticed a martin with unusually droopy wings perched on the porch of their Purple Martin house.  He flew away when they investigated with a ladder but one of the apartments was jammed with five other stuporous martins.  The entry to another apartment was blocked by a dead bird, and when he was removed another five birds flew out the now open door.  What’s going on?

Purple Martin

male

As you probably know Purple Martins are long distance migrants. The older scouts first arrive in the Chesapeake region in the second half of March, seeking their prior year’s nesting site.  The younger birds make the long trip from South America up to four weeks later.  The martins are the largest New World swallows and the only swallows displaying sexual dimorphism–the sexes look different. The eastern subspecies has the unusual trait of almost entirely depending upon man-made cavities for nesting.  Hundreds, perhaps thousands of years ago Native Americans in the east started hanging hollowed-out gourds to attract the sociable martins.  European settlers noticed this and expanded the practice which we continue today.  After thousands of generations of birds using these man-made nesting sites the eastern martins have essentially abandoned the use of natural cavities.

Purple Martin

Click on any photo to zoom

The concept of long distant and massive bird migrations has not always been known.  This makes sense since until the end of the 15th century we weren’t even aware of the distant continents themselves.  There was a general idea that the disappearing fall birds were hibernating somewhere, just like the frogs, turtles, and some mammals.  I’ve read old accounts of torpid spring martins that were assumed to be waking up from their winter’s sleep and wonder if they were describing the same behavior of our martins last month.

Purple Martin

Progne subis

So here’s my theory of what’s going on with the martins.  They are tough birds but after a two thousand mile migration their body weight is significantly reduced and the birds are vulnerable.  The ill-timed cold snap and rains greeted them in their already weakened state making it difficult to fly, or even avoid an oncoming car.  Martins usually forage during flight, but if they are too weak to fly hunger will compound their plight.  Possibly the flying insects they feed on were also in short supply due to the inclement weather.  I’ll bet they were huddled in the apartment and on the dark road in a last desperate search for warmth.  In the open they were clearly easy prey for predator hawks as well as the squashing cars.

Let me know if you’ve noticed similar behavior or if you have any additional thoughts.  It may well be a tough breeding year or two for the martins, at least in our neck of the woods.