Summer Bird Identification Quiz

Although many North American bird species completed their spring migration months ago, some are just now beginning to set up territories and nest on their breeding grounds.  With that in mind, I present another short identification quiz for the summer months!

1.  This species may be seen migrating late, and some individuals linger in areas outside of the breeding range.

2.  Look for this species in woodlands, especially near water.

3.  The species in this photo is also a bird of woodlands.

4.  In the photo, one of the clues to this bird's identity is hidden.

Answers:

1.  The American White Pelican is widespread across much of North America, and its winter range extends as far south as Central America.  It migrates across wide swaths of North America and breeds in several locations west of the Mississippi River.  Some nonbreeding individuals remain on lakes and other large bodies of water in the eastern portions of the U.S.  Unlike the coastal Brown Pelican, the American White Pelican does not dive for its prey, but instead forages for fish near the surface.  Groups will work together to more efficiently pursue their prey.

2.  Unsurprisingly, a significant clue here is the yellow throat!  Yellow-throated Warblers are far from the only wood warblers with this field mark, however.  For example, there is the widespread Common Yellowthroat, a species of thickets and marshes.  The western Grace's Warbler has even more similar features to the Yellow-throated Warbler: a gray back, white wing bars, black streaks on the sides, and a yellow throat.  The Yellow-throated Warbler's black mask and white eyebrows, though, are distinctive.  

Yellow-throated Warblers will sometimes conceal their nests in the Spanish moss that frequently grows in the wet, wooded habitats that they prefer.

3.  While the widespread and familiar Red-tailed Hawk is commonly found in more open environments, the Red-shouldered Hawk is adapted to woodlands.  The juvenile Red-shouldered Hawk in the photo lacks the rust-colored feathers of its parents, but its moderately slim build (compared to that of the stockier Red-tailed Hawk), banded tail, and streaked breast and belly help clinch the identification.  The Red-shouldered Hawk also lacks the pale "V" marking that can be seen on the back of a perched Red-tail.  

Because they tend to frequent swampy forests, Red-shouldered Hawks feed on a variety of animals, including frogs, snakes, and lizards.

4.  One clue may be hidden, but the white-spotted underside of the tail, the rust-colored wing feathers, and the pale underparts all point to this being a Yellow-billed Cuckoo.  The yellow mandible would be another useful field mark in regions where the Black-billed Cuckoo also occurs.  Cuckoos use their thick bills to catch hairy caterpillars, among other prey items, and tent caterpillar outbreaks may provide excellent conditions for viewing these usually secretive birds.  Unlike the Common Cuckoo, which breeds in Europe and Asia, North American cuckoo species only rarely practice brood parasitism, preferring to build their own nests and raise their own young.  

Swainson's Warblers

My first “sighting” of a Swainson’s Warbler wasn’t really a sighting at all.  I was birding one of the local sewage treatment ponds with my then-mentor, and I heard an unusual song coming from the woods behind us.  My birding mentor identified it, but to try to find the singer in the dense, swampy woods would have been futile.  I didn’t encounter another Swainson’s Warbler until the fall of that year, when one showed up in a thicket behind my house, walking around in the leaves less than five feet in front of me.  After this, I was able to hear, and occasionally glimpse, Swainson’s Warblers many times during the spring and summer.  This elusive bird, once practically unknown to me, was present in a surprising number of places.

The Swainson’s Warbler is very local and difficult to see but is not an exceptionally rare bird over much of its breeding range in the southern United States.  It does have the distinction of being elusive enough to escape detection by ornithologists searching for it for decades.  Two of the most famous cases of “lost” avian species, the Ivory-billed Woodpecker and the Bachman’s Warbler, also had a history of being spotted once, then suddenly disappearing, not to be seen again for years.  These species are legendary for their secretiveness, but the Swainson’s Warbler also had a long history of disappearance and then rediscovery, before regular studies confirmed many facts about its once little-known lifestyle. 

The drab appearance of this diminutive creature seems to point to one reason it was overlooked for so long.  At first glance, the Swainson’s Warbler does seem unremarkable, especially when compared with other North American wood-warblers.  A small bird, but large for a warbler, the Swainson’s Warbler measures about five and a half inches from beak tip to the end of its short, slightly notched tail.  The bill, in fact, is different from that of most other warblers in being relatively long and sharply pointed.  The bird’s upperparts are grayish-brown, a dead-leaf color that serves as an effective camouflage.  As counter shading, the underside of the bird is a pale gray or whitish shade, but some individuals show a tinge of yellow in this area.  The crown of the Swainson’s Warbler is a warm shade of brown, making it look nearly chestnut next to the extremely drab upperparts.  The bird also has a faint eye-line on the grayish face, and its head is very flat at the forehead.  The warbler’s long, pink legs provide a clue to its lifestyle; it spends much of its time walking on the ground—an unusual behavior for a warbler—as it forages for invertebrates in thick leaf litter.

These features reveal much about the habitat of the Swainson’s Warbler, and in fact the real difficulty ornithologists had in studying this bird was the impenetrability of this habitat.  The Swainson’s Warbler prefers dense, swampy woodlands with thick undergrowth and a sparse ground cover, leaving the forest floor open to falling leaves and creating the slowly-decaying microhabitat that many species of invertebrates use.  Although it is not absolutely necessary, cane is often a component of this habitat; where stands of cane are present, the warblers build their nests in them near the ground.  Other stiff understory plants such as palmetto are, of course, also used to support nests.  In the northern areas of its range, parts of the Appalachian Mountains, the Swainson’s Warbler retreats into a very different habitat: mountain laurel and rhododendron are the usual understory plants in these ecosystems. 

Regardless of the plants making up the forest undergrowth in Swainson’s Warbler territory, the bird is extremely difficult to locate.  One of the few clues to its presence is its song, a loud, clear Whew whew whew whip-poor-will that falls in pitch, rising again at the last note.  The song is similar to that of the Louisiana Waterthrush, but the waterthrush’s song ends with a jumble of short trills and sharp notes, rather than the clear, ringing notes at the end of the Swainson’s Warbler’s.  The song may be loud for a tiny bird, but the singer is extremely hard to see.  It nearly always chooses a secluded perch somewhere in the upper mid-story level of the woods.  If the bird senses that it has been detected, it flies quickly to a new perch and sits there silently for several minutes until “danger” has passed, often to the chagrin of a birder wishing to see it!  I once tried to creep up on a singing Swainson’s Warbler, and the best view I got was of the bird’s tail end as the bird—having detected me—darted into a cane thicket.  But during migration, even normally shy birds like the Swainson's Warbler can be seen feeding out in the open, far from dense cover, when songbirds of all species engage in atypical behavior in order to exploit more food sources.

Swainson's Warbler -- pen and ink

If the Swainson’s Warbler is easy to overlook now, over a century ago it was barely known to exist.  The habits of the Swainson’s Warbler helped to keep its most basic life functions secret for decades; discovered by Alexander Wilson in 1832 and described by John James Audubon in 1834, it was nearly unknown and wasn’t reported again until William Brewster and Arthur T. Wayne, two pioneering American ornithologists, found it in South Carolina in 1884.  Unfortunately, after this discovery, the species was again unstudied for many years.  Among other things, these naturalists documented its nest for the very first time.  Since the 1930s, however, when birding became popular, we have learned much about this warbler.

One of the crucial details of the bird's life history—its nesting behavior—was first documented by Brewster and Wayne.  The female Swainson’s Warbler constructs the nest, a somewhat messy, bulky cup composed of twigs, leaves, and vine tendrils.  It is lined with a wide variety of materials, including grass, mosses, bark, and hair, and is usually built only a few feet up in the vegetation.  The eggs are an unmarked white—probably an adaptation to the secluded nature of the nest site.  Most birds with well-concealed nests have pale eggs, since the eggs themselves don’t need camouflage.  This is very common in cavity-nesting birds, and the nest of the Swainson’s Warbler is so well hidden that it almost functions as a cavity—it could pass for just a clump of dead leaves if seen by a casual observer.  The female seldom leaves the nest during the incubation period; she alone hatches the eggs, which takes 13 to 15 days.  Both parents tend the helpless, altricial young until they fledge, ten to twelve days after hatching.  Apparently the chicks are fed on the same kinds of insect larvae, spiders, and millipedes that constitute the adults’ diet.  The long, pointed beaks of the warblers enable them to probe the crevices of dead leaves and even the top layer of forest soil for their prey.  As they shuffle around on the forest floor, they will even flip dead leaves over with their bills to inspect the undersides, causing a slight rustling sound similar to that made by other southeastern forest species, such as the Eastern Towhee. 

Although the Swainson’s Warbler is an uncommon and fairly local species in most of its range, exceptionally good breeding habitat can support far more than the usual number of nesting pairs; up to 44 singing males have been reported in some areas.  The Swainson’s Warbler is, unfortunately, facing many of the same problems that are contributing to the decline of other Neotropical birds.  Because it generally prefers dense woodlands with canebrakes, it is losing habitat on both its breeding grounds and its wintering grounds in the Bahamas, Cuba, Jamaica, Mexico, and Belize.  The unique Appalachian population, which some scientists believe to be a distinct subspecies, has declined precipitously.  In areas where its habitat is badly fragmented, the Swainson’s Warbler is also susceptible to brood parasitism by cowbirds.  Due to these factors, the National Audubon Society has placed the Swainson’s Warbler on its WatchList as a species of global conservation concern.

It’s amazing to think of the millions of years that helped shape the unique behaviors and adaptations of this unusual little bird.  Though we now know a great deal about its habits and place in the ecology of the forest, it took well over a century to discover them, and there are still secrets that it has yet to relinquish. The mysteries behind animals such as the Swainson’s Warbler are constant reminders of how much more there is still to learn about the natural world around us.

References:

Audubon WatchList 2007, National Audubon Society.  http://www.audubon.org/news/audubon-watchlist-2007.

A Field Guide to Warblers of North America.  Dunn, John, and Garrett, Kimball.  Houghton Mifflin, Boston and New York.  1997.

A Field Guide to the Birds’ Nests.  Harrison, Hal H.  Houghton Mifflin, Boston and New York.  1975.

Birds of Mississippi.  Turcotte, William H., and Watts, David L.  University Press of Mississippi, Jackson.  Mississippi Department of Wildlife, Fisheries and Parks.  1999.

The Cornell Lab of Ornithology’s Guide to Birds of North America, version 3.  2001.

The Summer Redbird

While the Northern Cardinal is the most familiar “redbird” in southeastern North America, the region hosts another rosy-plumaged songbird species that is also quite common, if somewhat more secretive: the Summer Tanager.  Catching a glimpse of one of these migratory birds may be difficult at times, but, if you learn to recognize their vocalizations, you may find them in a lot of places that you might not have expected.  The main call of this species is a dry pik-i-tuk-tuk, while the song is a slurred, throaty warble—smoother than the more separated phrases of the American Robin.  Because Summer Tanagers—and most tanager species, in general—tend to forage in the middle and upper branches of trees, seldom venturing close to the ground, the sounds that they make really are the most obvious signs of their presence in a given area.  Mixed forests, particularly pine-oak woods, are the preferred habitats for this species.

If you do manage to spot a Summer Tanager after hearing its song or call, it’s generally pretty easy to tell whether the bird is male or female.  Fully adult males have rose-red feathers all over.  Adult females are more variable, and can be anywhere from a slightly greenish yellow to an orange-yellow with hints of red.  

Adult male Summer Tanager

Female Summer Tanager

Notice that I said it’s generally pretty easy to tell the sexes apart.  Identification becomes slightly more complicated in the fall, when first-year males can have smatterings of red in their plumage or even an overall orangey appearance, just like female tanagers.  However, the young males usually have more red on the undertail coverts than the adult females do, so it’s sometimes possible to tell them apart.  Additionally, although some first-year female Summer Tanagers may look almost identical to some adult females, it’s more typical for them to be a bit drabber in color.  At any rate, studying the variety of tanager plumages during the autumn season can be an interesting project!  And, when spring rolls around and the tanagers return from their wintering grounds in Mexico, Central America, and the northern portion of South America, most of the young males will have plumage in a patchwork of red and yellow, as in the photos below.  It takes another year for their yellow feathers to be completely replaced with red. 

Preening immature male Summer Tanager

 

Immature male Summer Tanager

Summer Tanagers feed mainly on insects and fruit, and this is evident from the shape of their bills, which are stouter than those of exclusively insectivorous species, but slimmer than those of seed-eaters.  Actually, most people should probably be thrilled to have tanagers around, since the birds’ favorite insects to consume are bees, wasps, and hornets!  One of my earliest Summer Tanager sightings was of an adult male casually catching paper wasps high in a sweet gum tree in my backyard, and I’ve witnessed countless other tanager and hymenopteran interactions since then.  If there isn’t too much ambient noise, then you can sometimes even hear the *SNAP* of a tanager’s bill as it closes on the bee or wasp.  The tanager will then sometimes vigorously rub its prey against a tree branch before swallowing it whole and, later, regurgitating the tough, indigestible bits of insect exoskeleton.  Yep, hawks and owls aren’t the only birds to produce pellets; most species do.

I have never seen an active Summer Tanager nest—perhaps surprisingly, considering how interested I am in birds’ nesting habits.  However, monitoring a nest if I found one would probably not be too difficult, since tanagers prefer building on branches over open spaces and gaps in the woods.  There would be minimal vegetation in the way!  The usual number of eggs for the species is three to four, which are laid in a cup-shaped nest of grasses and leaves.  Females do the incubating, but both parents feed the young throughout the nestling stage and for at least a few weeks after the fledging.  Because Summer Tanagers are Neotropical migratory birds, developing survival skills during their first summer and autumn is crucial; after all, they don’t get any do-overs during that first grueling and hazardous journey to the wintering grounds.  If they make it back to the breeding grounds in the spring, then they can start to claim nesting territories for themselves, continuing the cycle.

Although summer is nearly over, there are still plenty of opportunities to see Summer Tanagers in their breeding range before they depart around mid-October.  Listen for the calls, watch for the wasp-catching behavior, observe the varied plumage patterns, and just enjoy the presence of our other “redbird.”

Source:

Robinson, W. D. (2020). Summer Tanager (Piranga rubra), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.sumtan.01

The Blue-headed Vireo: A Winter Songbird

In only a short time, the woods will be filled with the color and song of newly-arrived migrants: warblers, gnatcatchers, tanagers, and vireos, among others.  The Yellow-throated Vireo is one of our earliest migrants, and Red-eyed and White-eyed Vireos are some of the most numerous spring and summer forest birds, but even in the late days of winter there is a species of vireo living secretively in woods of the Southeast: the Blue-headed Vireo.

Blue-headed Vireos are hardy winter residents in the southern states.  They can be found in both upland and lowland habitats, in mixed or coniferous forests, where they feed on insects gleaned from bark, and also a few small fruits.  Like most vireos, they have a loud, scolding call, and their song is a series of short, whistled phrases.  Although they are usually silent in the winter, on warm days they can sometimes be heard singing.

The Blue-headed Vireo was originally grouped with two other species, the Plumbeous and Cassin’s Vireos—both of which occur in western North America—as one species, the Solitary Vireo.  It may be not be used anymore, but this name is still descriptive; outside of the breeding season, Blue-headed Vireos are rarely seen with other members of their species, preferring instead to forage with chickadees, titmice, warblers, and kinglets.  In fact, one of the best ways to locate one is to search through these flocks of small, jittery songbirds, until the slower, more deliberate movements of this reclusive bird catch your eye.

Once you find a Blue-headed Vireo, take the time to appreciate the colors of its plumage.  The namesake bluish-gray head contrasts with the bold white “spectacle” marks around the bird’s eyes.  The back is bright olive, and the wings have prominent yellowish wing bars.  The underparts are white, with yellow flanks.  The heavy, slightly hooked bill is very different from the thin, almost straight bills of the warblers and kinglets that the vireo feeds with.

This songbird arrives for the winter in October and departs for more northerly regions in mid-April.  Be sure to get out into the field to spot the colorful Blue-headed Vireo and other wintering songbirds!

Winter Frogwatching

If you live in the southeastern U.S., you’re probably used to the discrepancy between the timing of the seasonal changes that you observe and the "official" dates on your calendar.  During the winter, temperatures often climb to the 80s; brightly-colored flowers dot the lawns; resident birds start to seek out nesting territories in the woods and fields; and snakes, turtles, and (in some areas) alligators begin to stir in lakes and ponds.  Breeding frogs, taking advantage of the rain and the warmer temperatures, also put in appearances during this period.  While many frog species in the southeastern states hibernate through the winter and are not active until March or April, a few are commonly heard calling before the trees leaf out.  If you live in Mississippi, the species that you are most likely to encounter during the winter are chorus frogs, members of the Pseudacris genus.

The spring peeper (Pseudacris crucifer) is probably the most abundant of these “winter” chorus frogs.  I would venture to say that most people in the southeast are very familiar with the piping call of this tiny amphibian, but for those who aren’t (or those who would like a refresher), the U.S. Geological Survey has a recording.  From around late January to early April in Mississippi, you might hear this distinctive call in almost any wooded habitat near water.  Spring peepers spend much of their time in dense vegetation near the ground, so they are difficult to see—beneficial for them, but a pity for us, because they have very pretty, if subtle, patterns: dark brown leg stripes and a dark-brown x-shaped marking on a lighter brown background.  The camouflaging coloration and retiring habits are useful predator-evasion adaptations.

A close relative of the spring peeper, the upland chorus frog (Pseudacris feriarum) is fairly common in winter.  Despite their name, upland chorus frogs can be found in both lowland and upland habitats.  I would suggest listening for them in areas that are more open than the typical spring peeper habitat; old pastureland, fields, and meadows near sources of water are good places to check.  The trilling call of the upland chorus frog somewhat resembles the sound made when you run your thumb over the teeth of a metal comb.  In Mississippi, I have heard this species as early as the middle of December, and it may breed until April.  Like spring peepers, upland chorus frogs are secretive and extremely hard to spot.  One of their diagnostic field marks is a pale stripe above the upper lip, just below the dark stripe that extends behind the eye.  

Upland chorus frog - mixed-media painting

It’s worth pointing out that, in recent years, the range limits of the upland chorus frog and the very similar Cajun chorus frog (Pseudacris fouquettei) have been reevaluated.  Both species are found in Mississippi, but it’s likely that the Cajun chorus frog is restricted to the western portion of the state, while the upland chorus frog occurs farther east.  The call of the Cajun chorus frog is slightly slower than that of the upland.  

Happy listening!


Sources

The IUCN Red List of Threatened Species, http://www.iucnredlist.org/
USGS Frog Quiz, https://www.pwrc.usgs.gov/frogquiz/index.cfm?fuseaction=main.lookup

Midwinter Ramblings

This piece details some Noxubee County, Mississippi observations that I made many years ago.  Enjoy!

As is the case with any human activity, there are days when birdwatching reaps huge “benefits” for participants…you know, those days when something truly out-of-the-ordinary steals your attention and causes an immense adrenaline rush.  What constitutes an out-of-the-ordinary avian encounter is different for every person, but it always involves birds that are beautiful, graceful, especially fascinating, or rare—in other words, unusual.  Memorable occurrences such as an out-of-range species that provides a first record for a state or country, a trip to a wetland where thousands of waterfowl are congregating, stormy weather in spring bringing astonishing numbers of colorful neotropical migrant songbirds to a tiny patch of woods, and of course seeing a life bird all involve a feeling of intense concentration, combined with that welcome surge of adrenaline.

It’s a mild day in January.  For birders, midwinter days—as well as those of midsummer—seldom bring the intense excitement and anticipation that characterize other times of year, but this doesn’t concern me.  As I head out the back door, I notice the slight breeze and the freshness of the air; a cold front that moved in last night after the violent storms has left the temperature hovering at about 50 degrees Fahrenheit—although certainly not cold, it is cool enough for a light jacket, and chillier than it has been for a number of weeks.  The white airbrush streaks of airplane contrails mark an otherwise clear, azure sky—a far cry from the brooding grayness, rolling clouds, and fierce wind, rain and hail of yesterday.  I had originally figured that the conditions yesterday might have caused some birds to be more active today, but as I stand in the back yard, listening and watching, it crosses my mind that this will likely be one of the slower days of birding—in other words, an “ordinary” day.

Some of the first bird sounds to reach my ears are from the “regulars”—chickadees, titmice, and Carolina Wrens calling in the woods some distance away.  I walk across the soggy, gray lawn to the thicket behind the old outbuilding.  This thicket was mostly cleared out several years ago, but since then it has been allowed to grow into an impenetrable mass of tangled vegetation, the haunt of nesting Carolina Wrens, Northern Cardinals, and Brown Thrashers in summer.  Lush and green during that time of year, now the intertwined grasses, saplings, and vines are bare, gray, and brambly.  As I look closer, though, I notice that a few plants still have some green vegetation, and last year’s dry leaves dangle from the branches of some of the sapling oaks. 

A brief, scratchy call note, evoking the sound of a mechanical toy being wound, sounds from the upper branches of a large pecan tree in the thicket.  Oh, a Ruby-crowned Kinglet.  As I watch, the tiny bird flutters up to pluck small white berries from clusters growing near the pecan tree—poison ivy berries.  I follow these berry-laden branches with my binoculars, and with a sense of fascination mixed with horror, I find that the poison ivy has grown in the form of a large shrub, rather than the vines that I commonly see.  Its thick, hairy trunk leans against the old pecan tree.  Whoa.  I step away from the thicket and look at the sky, hoping to see a hawk or two.  As it turns out, one of the neighborhood Red-tailed Hawks is soaring overhead, the sun shining through the rust-red feathers of its rectrices—an unexpectedly beautiful sight.

Red-tailed Hawk

I walk down the slope of our backyard to the pond, and from there I go to the marshy ditch on the southeast side.  The “marsh” itself is home to willows, cattails, and various types of grasses, while pines and brushy woods grow on the northeast side of the pond.  White-throated Sparrows flush up in bunches in front of me and land in the woodland cover several feet away, exchanging sharp peek! calls.  They are most likely alarmed by the presence of this strange, flightless intruder.  If I’m careful, I can creep into the woods to look at these large sparrows, which are plumaged in subdued, yet striking, gray, brown, white, and yellow feathers.  Sure enough, I spot some of them as they dart in and out of the shrubbery.  A single, dry check note fills me in on the whereabouts of a Yellow-rumped Warbler, perhaps calling to its associates that are also somewhere in the woods, hidden from view.  

White-throated Sparrow

The churr churr call of a Red-bellied Woodpecker sounds faintly off in the forest.  I wonder where it is, exactly; most of the time, I see these woodpeckers close by in the yard, foraging in the old pecan and walnut trees.  Of course, this might not be one of the individuals that I see in our yard, but it easily could be—I’m sure that their territory includes much more than the few acres that comprise our property.  Barely detectable over the sound of the woodpecker are the little chipping calls of Pine Warblers moving through the pine thicket some distance away.  Pine Warblers tend to travel in small groups, and are seldom seen far from pine trees.  These warblers are too far away to locate at the moment, so I turn my attention to other things.  A small creek runs through these woods—barely a creek, actually… it appears more like a shallow ditch, filled with runoff from yesterday’s rain.  Just the fact that there is a depression, though, makes me think that the stream of water must run through here most of the time.  Both sides of the creek are lined with dense privet bushes, laden with clumps of small, bruise-colored berries.  Many naturalists hate privet with a passion; the invasive shrub is spread around in bird droppings, choking out native vegetation wherever it sprouts.  Although I’m not thrilled to see it here, the White-throated Sparrows darting in and out of its luxuriant growth seem to have quite a different opinion.

Red-bellied Woodpecker

It’s been several minutes now since I entered these woods, and I’m considering walking back out of them soon.  But wait—what is that little insect flying near the ground?  Looking closer, I see that it is a blue bottle fly.  It seems a little incongruous for one of these usually warm-weather insects to be out today—the 50-degree temperature surely takes a toll on its fragile metabolism. Not surprisingly, the fly buzzes around feebly before settling down on a dried stalk of grass.  A band of Blue Jays suddenly flies in, one of them giving a near-perfect imitation of a Red-tailed Hawk’s scream.   Then, just as abruptly as they arrived, the jays disperse into the woods.

Blue Jay

The White-throated Sparrows are starting to return to the territories from which I initially disturbed them.  They are settling in for the evening.  The sun will set soon, and it seems like a good time to turn in, so I head back to the house.  On the way, I stop to admire the faint pastel colors just beginning to appear in the sky.  It’s a nice ending to this midwinter day in the field, and a reminder that not all exciting birding experiences must be intense.  In fact, I wonder if an unending stream of amazing, adrenaline-pumping experiences would just tend to blend together, as the “ordinary” days do.  On the other hand, as self-proclaimed naturalists, finding something to enjoy in every outing should be one of our biggest priorities—and it’s rarely a difficult task to discover something worth watching in nature’s fascinating show.

Invasive Trees, Shrubs, and Vines

This is a consolidation of two of my earlier posts about invasive plants in the southeastern United States.  Invasives are simply nonnative species that cause significant harm to ecosystems.  Not all nonnative plants are invasive, but the invasives are very likely to be the ones that you notice on a daily basis!  Because the list of exotic plant species present in Mississippi alone (from this site: https://www.se-eppc.org/mississippi/) is lengthy and still increasing, I thought it made sense to focus on the invasive trees, shrubs, and vines that I commonly see in my part of the state.

Let’s start with trees.  A couple of quick definitions: although there are some exceptions, the general rule is that trees have a single woody stem or trunk, while shrubs have multiple woody stems/trunks.  Most of the trees that I regularly observe are native to my area, but, every so often, I will come across an invasive species or two—especially near urban settings.  Some commonly-seen cultivated plants, such as the ginkgo (an ancient, living fossil species that was wiped out across much of its range during the Pleistocene Ice Age) are basically innocuous, but others, such as the Bradford pear, can cause extensive damage to native ecosystems.  The Bradford pear is actually a cultivar of the species Pyrus calleryana, the Callery pear, which the United States Department of Agriculture introduced from Asia to the United States in 1916 to combat blight in the common pear, Pyrus communis.  (Obviously, common pears, along with other species that are used for food, largely benefit humans, so no one is suggesting that they should not be grown.)  Bradford pears are incapable of reproducing with other Bradford pears, but (as any fan of Jurassic Park would likely guess) this doesn’t stop them from proliferating; they just do it by cross pollinating with other calleryana cultivars, spreading this invasive species far and wide.  

One of several Callery/Bradford pears in the neighborhood.  Actually, this looks like it might be a "colony" instead of just one tree.

Chinese tallowtree, or popcorntree, is another common invasive.  Introduced to the U.S. in the 1700s, it is known for the waxy compounds found in its seeds, which have been used for candle- and soap-making.  Because the plants are toxic, few animals will eat them, so there is next to no biological control of their populations.  The USDA states that eradication is “virtually impossible,“ that the trees may begin reproducing at the age of only three years, and that they can continue breeding for 100 years– all of which make this species a particularly bad choice for North American naturescaping.  Don't grow it here!

The tallowtree tends to have a nice shape, which explains why it's so frequently planted.

Tallowtrees have heart-shaped leaves.  The seeds, which aren't in this summer photo, resemble popcorn.

In one sense, shrubs may be the stumpy cousins of trees, but their lushness more than compensates for that.  Along with tree saplings, shrubs comprise the understory layers in forest ecosystems.  However, invasive species, such as privet, don't always need to grow within wooded areas; they frequently thrive wherever their seeds have been dropped.  While several introduced privet species range across North America, the most common in the mid-southeastern region is Chinese privet.  There seems to be some conflicting information regarding when, exactly, Chinese privet was introduced to the United States—some sources say 1852, while others, including the previous link, say 1952.  The latter date might have been a typo, since the 1852 date shows up in sources such as the websites for the USDA, the University of Florida’s Center for Aquatic and Invasive Plants, and the Texas Invasive Species Institute.   

Chinese privet in the summer.

Privet leaves and unripe fruits.

At any rate, Chinese privet has become well established outside of its native range—so much that United States and regional noxious plant legislation isn’t even concerned with it and other privet species.  Eradicating privet from the U.S. is basically a lost cause.  Its fruits are eagerly consumed and widely spread by birds and other animals; it possesses tough, hardy, evergreen foliage; it forms extremely dense thickets; and, if cut, it regenerates quickly from its extensive underground root systems.  Several privet hedges in the neighborhood where I live have been cut before, but that didn't stop them from coming back with a vengeance.

  

A mockingbird and privet, photographed in Arkansas in 2013.  Birds are attracted to privet berries.

I have written about two bird nests—White-eyed Vireo and Northern Cardinal—that I observed in a thorny olive (or thorny elaeagnus) near the house.  The upper branches of thorny olives grow long and snake-like for the purpose of clinging to whatever is directly above them.  While this species—introduced in 1830 from Asia—lags behind privet in terms of invasiveness, it’s still a problem in many areas, forming spiky, impenetrable barriers.  There are a number of methods used to control thorny olives, but most of them are not particularly effective.  Essentially, even though the thorny olive does provide a certain amount of seclusion and protection for birds during the nesting season, there are much better options that don’t choke out all other vegetation in the ecosystem!

Long "tendrils" on the thorny olive.

The undersides of the thorny olive's leaves have silvery scales and sparse, tiny brown spots.

Another invasive shrub that can dramatically transform its environment is the multiflora rose (Rosa multiflora), a sometimes vinelike plant that was introduced from Asia to the U.S. in the 1860s.  Like kudzu, it was widely used for erosion control, and it also shares the ability to form impenetrable thickets.  Its thorny stems can attain heights of 10 to 15 feet, and it has attractive flowers that have five white petals with blunt or slightly indented tips.  Herbicides are effective at controlling multiflora rose, but follow-up treatments must be consistently applied to prevent germination of seeds, which can lie dormant, ready to sprout at any time, for up to 20 years in the soil.  

Multiflora rose flowers

We've looked at trees and shrubs, but what about vines?  One of the most out-of-control vines in the southeastern U.S. is so abundant that it has even had festivals created around it.  Kudzu (Pueraria montana) is a leafy, purple-flowered vine in the legume family.  Although it was originally imported to the U.S. (from Japan in 1876) as an ornamental, and was used for erosion control in the early 20th century, it has since become a noxious weed, infamous for covering entire landscapes and choking out native vegetation.  In ideal circumstances, it can grow up to a foot a day.  Controlling kudzu is difficult partly because of the stolons (or runners) that it produces, as well as rhizomes, or underground stems that produce roots and shoots; uprooting the plant so that it's incapable of forming new growth is next to impossible.  Herbicides can work if there is enough product to treat the many acres of ground that kudzu frequently smothers.

Kudzu creates odd, alien-looking landscapes.

Interestingly, one of the natural predators, the kudzu bug, was accidentally introduced into the U.S., with the first individuals recorded in Georgia in 2009.  However, because the kudzu bug tends to cause more damage to soybean crops than it does to kudzu, it can't be relied on as a biological control method.

Joining kudzu on the list of invasive vine species are two of the most widespread introduced legumes: Chinese and Japanese wisteria (Wisteria sinensis and W. floribunda, respectively).  Because these species can and do hybridize in the wild (rather like the red and black imported fire ant species), identification is often difficult.  Both species have long, compound leaves and clusters of purple or white flowers.  Given the toxicity of wisteria's fruits, native wildlife species are almost certainly not helping these plants to spread.  Instead, wisteria's quick growth and tendency to strangle and shade out native vegetation provide the explanation for its range expansion after its introduction to the U.S. in the early 19th century (1816 for Chinese wisteria, and about 1830 for the Japanese wisteria).  According to the Mississippi State University Extension Service, wisteria control is extremely difficult.

Wisteria flowers

Wisteria growing over another invasive: privet.

Another fairly horrifying invasive climbing plant is Japanese honeysuckle (Lonicera japonica).  Like all of the plants discussed thus far, Japanese honeysuckle was imported (in 1806) as an ornamental.  It has attractive and fragrant blossoms, and many people have fond childhood memories of sucking the nectar from these blooms.  Like wisteria, however, Japanese honeysuckle's thick, woody stems quickly strangle native vegetation—and, as with kudzu, biological control doesn't work.  In fact, there is no available biological control for Japanese honeysuckle.

Japanese honeysuckle flowers

Because of the limited ecological benefits and the difficulty of controlling Japanese honeysuckle, the Mississippi Forestry Commission recommends planting several native vines, instead—including crossvine, coral honeysuckle, and Virginia creeper.  That site and others, such as the Mississippi State University Extension Service, are well worth perusing for detailed information about native trees, shrubs, vines, and herbaceous plants.

In general, all of the introduced trees, shrubs, and vines described in this post flourish in their new environments due, in part, to a lack of herbivory by insects.  Native insect species didn't evolve with these plants, so they generally lack the ability to effectively utilize them.  Many studies have shown that insect communities tend to decline in the presence of nonnative plants.  A paper written by Berghardt et al. (2010) and published in the scientific journal Ecosphere (https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/ES10-00032.1) describes how Lepidopteran (that is, butterfly and moth) communities showed both lower population sizes and less species diversity on nonnative plants than on native ones.  Given the fact that many songbird species rely on caterpillars as a food source for their nestlings, the results of this study should definitely ring some alarm bells.  Fewer caterpillars mean less leaf damage, but also impoverished ecosystems.