Nature: Orange you glad you saw lots of orioles this spring?

A male Baltimore oriole plunders an orange/Jim McCormac

Columbus Dispatch

May 31, 2020

NATURE
Jim McCormac

This was the spring of the oriole.

Staggering numbers of Baltimore orioles appeared at feeders throughout much of May. This species, our most colorful blackbird, amazed many a feeder-watcher with their brilliant colors and sheer numbers.

Fans of backyard wildlife learned long ago that putting out sliced oranges would lure the orange birds. It’s not because style-conscience orioles want to color coordinate with their food. Rather, the sharp-billed birds regularly include nectar and fruit in their diet. To them, oranges are an irresistible treat.

Baltimore orioles will even dangle at hummingbird feeders, slurping at the tasty sugar water. Some people also put grape jelly out for them, which the birds will readily eat. However, jelly is not a recommended oriole food — there is no redeeming nutritional value to jelly.

Orioles’ calls are as conspicuous as their plumage. The birds regularly give loud flute-like whistles, creating a wonderfully melodic soundscape.

Back to the numbers. I cannot recall a spring with as many orioles being seen and reported on. Many people who target them with fruity handouts were stunned by the flashy displays. Bill Weaver of the Newark area sent me an amazing photo of his sister’s oriole feeding operation. She attracted as many as 27 birds at one time. The yard was awash with the flashy birds.

Attracting numbers like that also will provide a showcase of varying plumages. Male Baltimore orioles are the showiest. These sharp-dressed blackbirds are resplendent in crisp orange and black plumage. The bird’s name was bestowed by early naturalist Mark Catesby. He was reminded of the family colors of Lord Baltimore, Cecil Calvert, the first proprietor of what was then the Province of Baltimore.

Among the ranks were plenty of female orioles. First-year females — those born last year — can be rather dull: mostly brownish-gray with orange tinges on the breast and tail region. Females brighten with age, and older ones can become nearly as orange as males, but they lack the ebony hood and back.

The Baltimore oriole’s lesser-known relative, the orchard oriole, was a minor part of the invasion. Although far fewer in number, many people were excited to see this smaller species appear in their yards for the first time.

A glance at eBird, a data repository of bird sighting hosted by the Cornell Lab of Ornithology, showed Ohio blanketed by oriole sightings. Such numerous sightings weren’t just limited to Ohio, either — birders over much of the eastern U.S. reported above-average oriole numbers.

The million dollar question: Why so many orioles? Like most things in nature, multiple factors probably contributed to the big numbers. Orioles have become increasingly attracted to feeding operations, and more people are trying to attract them. There probably is an overinflated sense of their commonness as compared with the myriad bird species that never visit feeders.

This was an unseasonably cold spring, which would have made insect stocks harder to access for migrant orioles. Also, flowering seemed delayed — orioles often take nectar from flowers — and in some cases, flower mortality probably was high because of late freezes. Floral paucity might have pushed higher-than-normal oriole numbers to feeders.

Most Baltimore orioles winter in the tropics of central and northern South America. Navigating this long migratory corridor back to northern breeding grounds is a hazardous endeavor. As the human population has burgeoned, we have thrown up an ever-more-perilous gauntlet that migratory birds must run.

A major mortality factor is collisions with Illuminated skyscrapers and other buildings, as most songbirds migrate at night. Vehicle roadkills also are common. Self-quarantining and temporary business shutdowns caused by the COVID-19 pandemic have led to an enormous reduction in human activity related to bird mortality.

Dimmed buildings and less traffic might have meant fewer bird kills. I wonder if the lack of human activity at the peak of spring migration allowed for higher than normal survivorship among orioles and other migrants.

Maybe there truly were more orioles around this spring to grace us with their presence.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

Orioles and elms

A good-sized American Elm, Ulmus americana, stands alone on a field edge. Its whiskbroom shape is apparent even from afar. I tend to notice big elms, and generally pay them more than a passing glance. The American Elm is still a very common tree in Ohio, but big ones are scarce.

In 1928, Dutch Elm Disease was first detected in North America, and it spread like wildfire. It is caused by three species of microfungi, two of which afflict trees on this continent. The fungi is spread by a trio of bark beetles. Once a tree is infected, the tree attempts to thwart the spread of the invader by plugging its xylem channels, which transport various nutrients and water throughout the plant. This ultimately fails, and the elm dies. Trees usually succumb before reaching the size of the specimen in this photo, which I found last Thursday at Killdeer Plains Wildlife Area. Most large elms that I see are isolated like this one is; it may be more difficult for the vector beetles to reach them.

When I slowed to admire the stately tree, I noticed it bore a nest. You can see it in the branches furthest to the right in the photo. This is not the first time that I have seen such a nest in a surviving mature elm. In fact, when I do find such a tree I scan it specifically for this type of nest.

A work of art indeed! The beautifully woven basket of a Baltimore Oriole, suspended from the elm's slender branches. The fact that it is still in the tree, and in good shape at this late date, is a testament to the oriole's basket-weaving skills.

There is no question that Baltimore Orioles have a propensity for siting their nests in the boughs of American Elms. Before Dutch Elm Disease appeared on the continent and laid waste to our elms, this tree was commonly used as a street tree. Avenues and boulevards would be lined with elms, their overarching branches connecting to form a shady arbor over the roadway. Numerous accounts describe the colorful orioles that graced the elms, delighting people with their musical flutelike whistling and brilliant splashes of orange. A paper entitled The Nesting Habits of the Baltimore Oriole appeared in a 1930 issue (vol. 42:4) of the Wilson Bulletin. In it, the author describes nine nests that occurred along a street in Sigourney, Iowa in the summer of 1927 (pre-DED). Eight of the nests were located in American Elms. Such pro-elm favoritism was probably the rule in midwestern towns and cities prior to DED.

Why the orioles' preference for elms? Probably for safety's sake. The spindly, drooping ultimate branches of elms prohibit access to many predators. A raccoon would certainly never make it to a nest such as shown in my photo. Nor would that most effective of avian nest predators, the black ratsnake, I would guess. Fortunately orioles have proven to be adaptive, and have jumped the arboreal ship to other trees for nesting purposes. A favorite is the Eastern Cottonwood, Populus deltoides.

I have watched orioles create their ornate hanging baskets on a number of occasions, and it is a remarkable thing to observe. Here, a female busily weaves her nest in a maple in northern Michigan. Somehow she takes an insensible tangle of grasses and plant fibers, and in a flurry of activity crafts a sturdy, well designed cup from the mess in just a few days. I couldn't do such a thing armed with my ten fingers.

The oriole's intricate cup spawns one of the world's most colorful blackbirds, named for the colors of the coat of arms of Sir George Calvert, who was the first lord of the Baltimore colony. The females, who one might argue do most of the heavy lifting in the oriole's world, are much more muted in plumage than is this showy male.

No dummies, most of our Baltimore Orioles are now in the tropics of Central America where they will ride out the winter. Come late April, their cheery whistles will once again ring from the Ohio treetops, every bit the harbinger-of-spring.

Oriole, eating tent caterpillars!

About a month ago, immediately following the Ohio Ornithological Society's annual conference at Shawnee State Park, I got to spend some field time with two of Ohio's very best bird photographers. That would be Dane Adams (left) and Brian Zwiebel, pictured above plying their trade. Along with Jan Auburn, we made a rather short but steep trek to the summit of a tall "mountain" near the Shawnee lodge that offered treetop views. That's some heavy photographic artillery mounted on those tripods. Both guys shoot Canon gear, and Brian was working with a 600 mm lens (I think), and Dane had even a bit more oomph with 800 mm of lens. You can reach a longs ways into the leaves with gear like that.

We had a great time talking photography and watching numerous warblers and other songbirds move through the nearby trees. As a bonus, the cement pad at the hill's crest served as an attractant to hill-topping butterflies of many species.

On the hike up, and everywhere else we went that weekend, we noticed plenty of eastern tent caterpillars, Malacosoma americanum. This species is certainly one of our better known caterpillars, due to their habit of constructing conspicuous silken shelters. These caterpillarariums are nearly always placed in the fork of a black cherry tree, Prunus serotina, as is the one pictured. Tent caterpillars, which are the larvae of a rather handsome moth, seem to have boom and bust years. Some years the silk nests are seemingly everywhere, others relatively few can be found.

Most caterpillars go through five growth phases, each one termed an instar. At least two and perhaps three different instars are present in this photo. Following each instar, the caterpillar sheds its skin and emerges larger. Following the ultimate instar, it fashions a cocoon in which it will transform to the adult moth.

The silken tents in which the animals live communally until their last instar serve several purposes. Foremost, the dense sticky silk offers superb protection from would-be predators, especially parasitoid flies and wasps. Both are prolific enemies of caterpillars. Also, most songbirds will not deal with the dense silk, so for the most part the caterpillars are also safe from the feathered crowd.

Come nightfall, and the temporary disappearance of most of the birds, flies, and wasps, the caterpillars emerge from the nest and radiate out into the tree to feed on cherry foliage. Come dawn, they crawl back into the shelter of the nest. The tent probably also serves as a sort of greenhouse, with an elevated internal temperature that speeds the digestive process of the caterpillars within. Note all of the little blackish flecks in the silk - that is all frass, or caterpillar poo.

A fully grown eastern tent caterpillar is rather handsome, painted as it is in blue, gold, black, and white. Nonetheless, it is mostly maligned by people who resent what they consider to be unsightly silken nests. Let it be noted, though, that this is a native animal and its depredations on cherry trees seldom do any lasting damage. And as we shall see, some interesting and generally much more appreciated animals make much use of the tent caterpillars.

Most birds do have trouble eating them, as the long stiffish bristles of the caterpillar will eventually clog up their digestive tracts. Most famous of the tent caterpillar-eating birds are the cuckoos, who seemingly eat them with impunity. This is because Black-billed and Yellow-billed Cuckoos can slough off and cast out their stomach linings if they become too spiked with caterpillar bristles. The bird is able to regrow its stomach lining and thus can regularly consume the bristly meals. For the most part, with at least one notable exception, it seems to be the cuckoos that are the primary avian predator of eastern tent caterpillars.

A quick aside: Next time you see a tent caterpillar nest with some caterpillars on the outside, go tap or otherwise disturb the nest. You'll probably see the same furious side to side thrashing as shown in my video. This behavior is most likely evolved to thwart predatory flies and wasps, and prevent these insects from laying eggs on the caterpillars. The motion also may function as an alert to other caterpillars who are outside the nest. My friend Paul Knoop observed a predatory Ichneumon wasp alight on a nest this spring and all of the visible caterpillars instantly began thrashing. He reports that within 30 seconds or so, all of the caterpillars had vanished back inside the nest.

Anyway and finally, to the object of this article. We had not long been atop the hill when we spotted a gorgeous male Baltimore Oriole fly into a nearby tree. Knowing the the colorful blackbirds were also fond of snacking on tent caterpillars, I suggested that Brian and Dane train their lens on a nearby, particularly scrumptious caterpillar nest. Sure enough, a couple minutes later the oriole dropped through the branches and approached the nest.

Dane, with his mega lens and skills at finding objects through blowing leaves and branches, managed a great series of shots, and he was kind enough to share them with us. In the photo above, the oriole has just alit and is inspecting the nest for victims.

One thing that I was always curious about was how orioles managed to eat bristly tent caterpillars without doing harm to their digestive tracts. Cuckoos, as we know, can simply regrow bristle-clogged parts, but insofar as I know, orioles do not have this ability. I was hopeful that a nice series of photos might cast light on the oriole's tentside culinary practices.

We can see in the above photo that the oriole has apparently pierced the skin of the caterpillar, and is drawing out the prized innards.

It appeared to us, and Dane's photos seem to illustrate this, that the oriole uses its sharp, finely pointed bill to neatly slice open a slit in the caterpillar, from which it could draw out the inner contents.

You can see the oriole tugging out the guts, as it were, without the need of swallowing the whole package bristles and all.

Like slurping a strand of spaghetti from a tubular plate. Baltimore Orioles are certainly known to dine on tent caterpillars, but I've never seen the techniques by which they do so explained. Thanks to Dane's fine photographs coupled with our field observations, it appears to be a matter of careful dissection and surgical extraction, thus avoiding the bristly outer skin.

Even the most reviled native animals, such as tent caterpillars, have value. Our superficial condemnation is often unjustified and all too frequently based on ignorance.

Thanks to Dane for sharing his great series of photos.