Saturday, July 26, 2008

Ruby-throated Hummingbird - Sex, Danger, and Physics

Last week I had to cut short my account of the Ruby-throated Hummingbird in order to conduct field observations on this diminutive subject - observations requiring the kind of labor appropriate to a muggy summer day - propped feet on the back porch.

Between sips of an iced ade and naps, I also researched the observations of others on this tiny bird. John James Audubon wrote elegantly about the male Ruby-throated Hummingbird’s tender courtship of his love: “how full of ecstasy he seems to be when his caresses are kindly received; how his little wings fan her, as they fan the flowers ... how his attentions are received with apparent satisfactions; how, soon after, the blissful compact is sealed; how, then, the courage and care of the male are redoubled; how he even dares to give chase to the Tyrant Fly-catcher, hurries the Blue-bird and the Martin to their boxes; and how, on sounding pinions, he joyously returns to the side of his lovely mate. Reader, all these proofs of the sincerity, fidelity, and courage, with which the male assures his mate of the care he will take of her while sitting on her nest, may be seen, and have been seen, but cannot be portrayed or described.”

Audubon’s description is wonderful, but I suspect that while making his observations or penning these words, he was sipping a frontier neighbor’s fermented corn squeezings, because he simply got it all wrong.

As a mate, the male hummingbird lacks sincerity, tenderness, and fidelity. There is no blissful sealing of a compact. His courtship display consists of a large, U-shaped flight which may climb as much as fifty feet. Then comes the “blissful compact,” which might best be described as “wham, bam, thank you ma’am.” A friend once described it as fast and violent; he described it as rape, except that the female does seem consensual.

Once the brief act is over, the female Ruby-throat is on her own to build her nest, incubate her eggs, and raise her young, which have probably been fathered by multiple males. The male provides no tender care or protection.

Meanwhile, the male continues to defend his territory. Forbush describes him as a gay wanderer with nothing to do but enjoy himself - a carefree bachelor we might say. But that hardly does his hormones justice. His sole purpose is to mate with as many females as possible, and to keep rival males at bay; he pursues his purpose throughout the summer. He is so driven that he neglects his own well being; territorial defense and copulation take precedence over everything. They also take a toll. Males may lose twenty percent of their body weight during the breeding season. They become ragged and weak. When breeding activity declines, then they feed again and rebuild their weight and muscle mass for migration. “This lifestyle comes with a cost: Female ruby-throated Hummingbirds live approximately 25 percent longer than males.”

Meanwhile, the female is doing the hard work ... and the dangerous work. The male can move quickly from his throne perch on a branch should danger approach. But a nest with eggs and young is stationary. “Ruby-throated Hummingbird females have been observed confronting and harassing tree-climbing snakes, hawks, crows, Blue Jays, Carolina Wrens, and Tufted Titmice.” They will often buzz humans and pets who get too close to their nest.

Early observers often commented on the Ruby-throat’s truculence and pugnacity; it seemed willing to attack any other bird, regardless of size, that somehow piqued its displeasure. Forbush shared the opinion of many that this “little bird seems to have few effective enemies. He is too agile and swift for them.”

But this tiny bird does have enemies and faces many dangers. Arthur Bent in his “Life History” collected a wide range of perils faced by the Ruby-throated Hummingbird. A couple of correspondents told Bent of finding a hummingbird caught in a spider web. One hummingbird was being wrapped tightly by the spider, held fast and able only to plea for help; its rescuer delicately unwound the mesh and freed the bird.

Bent also reports a hummingbird whose stomach feathers became stuck to the pointed stamens of a thistle flower. When finally removed, it had lost a few feathers but otherwise was unharmed and flew off. Less fortunate was the hummingbird in this report: “We were seated by the lotus-pool when a hummingbird flew and hovered over the pool. Suddenly a bass jumped from the water and swallowed the hummingbird.”

In the mid-1930s a Merlin was shot near the Louisiana coast; the contents of its stomach were analyzed and included the remains of a Ruby-throated Hummingbird, the only record, at the time, of a hummingbird having been found in any bird’s stomach.

Bent also records several instances of frogs capturing and swallowing Ruby-throats, and an instance of a huge dragonfly on the back of a Ruby-throat; it had seized the bird by the throat. It is a dangerous world out there.

Our Ruby-throated Hummingbird is a drab little bird. Both sexes, and juveniles, are dull green above - camouflage from predators looking down at green leaves and plants. The dirty white of their underside helps them disappear against the sky when a predator is looking up.

Most of the time the male has a black throat, except when he is facing the observer. Then his throat flashes a bright, iridescent, ruby-red. This iridescence, a characteristic of hummingbirds, is produced by complex structures in the feathers. Microscopic discs and air bubbles cause light of the correct wavelength to be added together, while other wavelengths are canceled out, producing, in the case of the Ruby-throated Hummingbird, his ruby-throat.

The science of the hummingbird’s iridescence is explained, in part, by the physics of light waves. But physics does not explain purpose. When the iridescent, ruby-red throat flashes before the observer, it does something. It excites bird watchers. And more importantly, during certain times of the year it drives the lady hummingbirds ga-ga.

Good birding.

Quotations from “The Sibley Guide to Bird Life & Behavior;” also Audubon’s “Birds of America,” and Bent’s “Life History. ”

Monday, July 21, 2008

Mississippi Kite - Cooperative Breeding Observation

On July 21, I received an e-mail comment on my June 28 posting on the Mississippi Kite from Scott Williams in Mississippi. I asked his permission to post the comment and share it with others. Here it is:


My name is Scott Williams. We live in extreme Southern Mississippi, near the Alabama state line. Actually we live near the small town of Lucedale, Mississippi.

I read your blog about the three Mississippi Kites causing a stir in [New England]. We actually watch our Kites do this ménage a twau thing every other year or so.

We think that we have finally figured out what is going on. We have a tall sweet gum tree about 40 yards from our house. Every year the same two Kites return from Argentina to our sweet gum tree and raise a family in the same nest.

The odd thing is the progression of events. Year one, one adult male and one adult female show up and raise a family in the same exact nest, in the same exact tree. We watch them breed. We watch them raise their one baby. We watch it learn to fly…and finally, about August 29th we watch the three of them leave for the season to return to Argentina.

Year two, nothing happens. We think that the three of them may just stay in Argentina, or maybe they just don’t make it to our sweet gum tree.

Year three, three adults show up in a group. We think that it is the mother and father and the adolescent chick from two years earlier.

My wife claims that she can recognize the chicks from the previous brood. She says that they communicate with her. (coo coo, coo coo).

The mom and dad mate, lay an egg and incubate it until it hatches. We think that the adolescent from two years earlier helps with repairs to the nest and helps feed the new chick.

This goes on all summer. The “teenager” helps out, but mainly just to bring a dragonfly to its new sibling every now and then. It mostly just sits around in the top of a tall pine and talks to my wife.

All joking aside, we believe that this “helper bird” is a grown chick from an earlier brood that is still attached to mom and dad. After the chick is raised from the new mating we think that the teenager finally goes out into the world on its own.

Follow-up e-mail giving me permission to use his comments:

We love our Kites. If they are coming, they usually show up at our place around April 28th or 29th and nest in the same exact nest that they have used before. Sometimes they do repairs to, or reinforce, the existing nest.

You would think that with a name like “Mississippi” Kites that they would be abundant down here in Mississippi, but that is really not the case. Many of my friends have never even seen one.

They are especially fun to watch as the chick nears maturity. The chick begins his exploring by flapping his wings in and around the nest. Later the chick will fly to nearby tree tops. However when mom or pop comes dive-bombing in to feed him he will make a bee-line to the nest to get the food that they bring.

Thank you, Scott, for this interesting follow-up. The speculation was that the third bird in NH might be a helper bird. Great to have someone who has observed this behavior.

"Cooperative Breeding" birds was the subject of an article in March, 2008, by Bob Engel of Marlboro College in the newsletter of Southeastern Vermont Audubon - Go to and click on Newsletter, then March, 2008. Link is on the right on this page.

Saturday, July 19, 2008

Ruby-throated Hummingbird

Walking through my garden, I felt something buzz past my head. It might have been a dragonfly, except dragonflies don’t land on branches and scold my intrusion into their realm.

For much of the day I had watched the “big bug” defend his territory - mostly the bright red blossoms of bee-balm, or anything else that he felt was his. The Song Sparrow had gone into hiding; the chipmunk ventured out rarely. The finches went elsewhere. Most of his aggression was directed toward his own kind - probably his own offspring. Young whirled about the blossoms, until from his perch overhead, he swept down, his flight forming a deep “U”, swinging from side to side like a pendulum - then darting out and chasing off all intruders - save perhaps for a female who might be receptive to another brood and thus to his amorous advances.

Gram for gram (ounces are simply too weighty for this little bird) the Ruby-throated Hummingbird is the most energetic and pugnacious of our eastern birds. I have written on other occasions of the tyrannical nature of the Eastern Kingbird, but for truculence and pugnacity, the kingbird is a distant contender to the Ruby-throat.

Forbush wrote of the hummingbird that he is “a mighty warrior, with greater strength and speed in proportion to its size than any other bird that flies. The flight muscles are relatively immense, and it is possessed of such spirit that it does not hesitate to attack any bird, no matter what its size, when occasion seems to require it. Kingbird, hawk, crow or eagle, all alike quickly feel the effects of the Ruby-throated Hummingbird’s displeasure. It has even been know to drive to cover a pompous Plymouth Rock rooster.”

“This little bird seems to have few effective enemies. He is too agile and swift for them. At times when he is not feeling truculent, he may allow some of the larger birds to chase him away from their nests, but I have seldom heard of the catching of a hummingbird by another bird.” (Forbush)

Hummingbirds occur only in the Western Hemisphere. Most of the 325 species occur only in the tropics. Eighteen species are found in North America, and east of the Great Plains, only the Ruby-throated Hummingbird is resident in the summer. ( Rufous Hummingbirds are reported quite often in the East during the Fall.)

The first European settlers in North America had never seen a hummingbird and included the tiny bird among the marvels of the country. In 1634, William Wood described it thus: “The Humbird is one of the wonders of the Countrey, being no bigger than a Hornet, yet hath all the demensions of a Bird, as bill, and wings, with quills, spider-like legges, small clawes: For colour she is as glorious as the Raine-bow; as she flies, she makes a little humming noise like a Humble-bee: wherefore shee is called the Humbird.”

The rapid wing beats (up to 80 wingbeats per second!) create a “hum” - hence the family name, “hummingbird.” In flight, hummingbirds can hover and fly backwards. In forward flight, they can reach speeds of up to 60 miles per hour.

They are best known for their fondness for nectar. They have long slender tongues which can reach far beyond the tip of their long bills. The combination of bill and tongue allows them to reach deep into blossoms for the energy rich nectar.

It was long thought that hummingbirds relied exclusively on nectar for their food. It is now recognized that invertebrates are important and essential to their diet. They will eat anything small enough to swallow including fruit flies, gnats, mosquitos, thrips, aphids, spiders, maggots, caterpillars, ants, and insect eggs. “Quickly flitting from flower to flower, they ingest both the fuel (nectar) required for such activity and the insects and spiders that help them meet protein, vitamin, and mineral requirements.” (Sibley)

The Ruby-throated Hummingbird gets its name from the brilliant ruby throat of the male. The female is better camouflaged with her green back and white throat and belly. As with many species displaying sexual dimorphism, the plainer female hummingbird does the nest building, incubation and feeding of the young. “After mating, the male apparently becomes a gay wanderer with nothing to do but to enjoy himself or to chase other birds. He spends much time sitting on a particular twig, which he chooses for his watch-tower and resting-place, and dressing his plumage ....” (Forbush)

Over two months ago, the male Ruby-throat resident in my yard claimed a twig on the end of a maple branch. From there he swoops to the feeder, patrols the bee-balm, lilies, and daisies, and maintains a truculent control of the neighborhood. The numbers of plain-colored hummingbirds that have begun to appear are probably his off-spring, though he shows little parental interest. Rather, it seems that he is more likely to display resentment that he must share his territory.

I sometimes worry that my hummingbird feeder is a fast-food junk-food for hummingbirds. (A reader told me about numbers of hummingbirds emptying her feeder in a day.) But as I watch the activity in my yard, the hummingbirds are not relying exclusively on the “junk-food.” Their visits to the feeder are only occasional. In fact, I see them on the bee-balm much more often than at the feeder. Even the young ones seem to know that they need more than just a sugar rush.

Hummingbirds feeding at flowers are acquiring fuel (nectar) and protein, vitamins and minerals, the latter in the form of insects and spiders. One common method by which hummingbirds hunt insects is by “hawking.” They perch on a bare open branch, watching for insects. Flycatcher like, they attack the passing insects. Ruby-throated Hummingbirds have been observed taking as many as thirty insects from a swarm in one hovering attack. Hummingbirds also feed by “gleaning,” searching new leaves for tiny caterpillars, turning over leaves the way some warblers do, or poaching food from other foragers. They will sometimes steal insects trapped in a spider’s web, as well as eating the spider, its eggs, and its young.

I would like to tell you more about female hummingbird breeding behavior, nest predators and other dangers to hummingbirds (such as spider webs during migration), or feather iridescence. But right now, I have field work on the Ruby-throated Hummingbird which demands my attention. I must sit quietly on my porch, with feet propped and an iced ade nearby and study my backyard hummer. It is a demanding way to spend a somnolent summer afternoon, but such efforts are necessary in the pursuit of Good Birding!

Quotations are from Forbush & May, “A Natural History of American Birds,” 1955, and David Sibley, “The Sibley Guide to Bird Behavior,” 2001.

Saturday, July 05, 2008

A Backyard Scolding

I was scolded yesterday. I was scolded for trespassing. I was scolded up one side and down the other. She made herself abundantly clear that I had no business walking where I was walking. She went on and on and on, even after I took her point, meekly apologized, and departed.

It wasn’t as though I had ignored no trespassing signs and wandered across a field that was closed to intrusion. I had not crawled beneath a barbed wire strand, scrambled over a closed fence gate, or otherwise breached some closed barrier that said, “Stay out.” None of those things.

I had done nothing more than walk slowly from my back porch, down a few steps to my lower lawn in order to sit by the river. I was on my property the whole time. She didn’t care. As far as she was concerned, this was her homestead exclusively, and she made her opinion very clear and at length.

I tell you truly - I was intimidated, by a shrew that Shakespeare could never have tamed, by a bundle of nervous energy weighing less than one half of an ounce. I was intimidated by a mother House Wren. She determined that I would keep my distance from the young in her nest hole. She was unhappy when I moved my old Adirondack chair forty feet from the bird house she had stuffed with sticks. She was upset when I sat quietly like a peeping tom, hoping for a glimpse of her going in and out of her nursery. Finally the scolding got the better of me and I slunk off as unobtrusively as I could.

My yard is not my yard this summer. It has been coopted by the House Wrens. At least two males sing, dawn to dusk, from opposite sides, even when they are also busy bringing food to nestlings. There’s a second nest somewhere, judging by the scoldings I get when I inspect the four o'clocks.

In spite of the scoldings, I am delighted. Two summers ago the resident male, in his zealous defense of territory, was careless crossing the road. I found him dead, the victim of a passing vehicle. His mate spent a silent mid-summer trying to hatch infertile eggs, then departed. Last summer, we had no House Wrens. For the first time in twenty-five years, the yard outside our bedroom window did not echo with the rapid, rolling rattles and trills of the House Wren.

When John James Audubon was roaming the continent in the early 1800s documenting birds with his shotgun and paintbrush, he found the Wood Wren, a dark brown bird, in the southern forests. In northern states, he knew the House Wren intimately, a semi-domesticated bird common in gardens, orchards, farmland. It was even present in the very center of early nineteenth century cities, where people were putting up little boxes for them to use as nests. But at the end of the breeding season, the House Wrens disappeared, and Audubon had no idea where they went. What he never discovered is that his Wood Wren and the House Wren are the same species. At the end of summer, House Wrens migrate from the northern farms and cities to the southern forests.

The House Wren has lived for so long in proximity to human habitations that we regard our yards , gardens, and shrubs as its natural habitat. In fact, it is a forest bird - in open forest, woodland edges, beaver ponds, and brushy swamps, his complex song, with a volume out of proportion to his size, proclaims his territorial prerogatives while she takes any natural cavity as a nursery for their young.

But the House Wren has also adapted easily and readily to human presence. We know it as a common occupant of the nest boxes we put up. Audubon saw House Wrens occupying such artificial cavities; he also saw them “satisfied with any crevice or hole in the walls, the sill of a window, the eaves, the stable, the barn, or the upper side of a piece of timber, under the roof of a piazza ... the pocket of an old broken-down carriage ...” and the list goes on. He painted his House Wrens nesting in an old hat, the mother bringing a spider to the young anxiously hanging out of the side of the hat while the male is on the lookout nearby.

“In Pennsylvania a pair of these birds had formed a nest,” Audubon wrote in The Birds of America, “and the female was sitting in a hole of the wall, within a few inches of my (literally so-called) drawing-room. The male was continually singing within a few feet of my wife and myself, whilst I was engaged in portraying birds of other species.”

The House Wren is a product of the woodlands where it sought out hidden cavities and caves for its nest; its genus is Troglodytes - “cave dweller.” It still chooses cavities and caves when it nests in its natural setting, and when it chooses proximity to human habitations.

House Wrens are a successful species because they are adaptable, and able to accommodate to human presence. They also pose little threat to humans; they don’t scarf huge quantities of grain or raid chicken coops. They eat bugs, which can be a nuisance and destroy crops. They are amusing - bundles of energy, constantly coming and going, flitting their upcocked tails, chattering vibrant songs, saucily scolding the neighbor’s cat, the presumed landowner, or any other intruder.

I suspect that the harridan wren who so scolded me yesterday is a product of the natural woodland habitat, and that she was reared where there was little need for accommodation to human presence. She has barely accommodated my presence.

When I watch her more closely, I realize that she is not really scolding me. She is distracting me. I hear her chatter and I see that she has food in her beak. I take a step closer, and she flies, always further from her nest. She does not begin to approach the nest until I begin to move away from it. She is very wary about giving away its location, even though the box is hanging on a tree branch and is clearly visible.

Wrens may be vocally loud and conspicuous, but that is a technique for drawing attention away from the hidden nest. Her continual scolding at my presence, finally brought her mate into the picture. He sang, and when I approached him for a closer look, he moved off, and sang again. Clearly he was drawing me away from the hidden nest in the box hanging on the branch.

Both wrens had enough mental power to distract me and lead me off, but not enough to recognize that their nest really was vulnerable, save for my beneficence. But then, I can not fairly criticize wrens for a lack of mental reasoning ability - not when my own species so often lacks that ability.

Good birding.


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