Jet airplanes cruise at 30,000 to 40,000 feet. Did you know that birds can fly at the low end of that range?
Birds’ respiratory systems are so efficient that they can pull oxygen out of very thin air. We know this because they migrate over the Himalayas.
Common cranes (Grus grus) are widespread across Europe and Asia, nesting from Norway to Siberia and wintering from Africa to southern China. Those that nest in eastern Kazakhstan and northwestern China fly over the Himalayas to spend the winter in India. They’ve been clocked at 33,000 feet!
Bar-headed geese (Anser indicus) nest in the Tibetan highlands and spend the winter in the lowlands of India. The shortest route from Tibet to the sea is to fly directly over the Himalayas, and so they do. They’ve been recorded at 29,600 feet and seen flying over Mount Everest! This video shows how they do it.
And even mallards, the ubiquitous ducks that eat bread at the boat launch, were seen migrating at 21,000 feet over Nevada.
Birds don’t need oxygen masks at those high altitudes. They just fly by.
(photo credits: All photos are Creative Commons licensed via Flickr. Click on each image to see its original:
View from a jet over the Himalayas by David C. Jones on Flickr
Common cranes in flight by Ján Svetlík on Flickr
Mallards in flight by Ken Slade on Flickr
Video from FantasticAnimal on YouTube)
John Scott holding a canary cage used in coal mines rescue training at Cannock Chase, UK (Image courtesy of the Museum of Cannock Chase. Copyright unknown.)
Today, a bird anatomy lesson.
You’ve probably heard the phrase “the canary in the coal mine” and know it refers to advanced warning of a danger. In the centuries before air quality instruments, miners carried canaries in cages into the mines to detect carbon monoxide and methane before they reached dangerous levels for humans.
Why did we use birds to detect bad air? Why not some other small animal?
Birds are uniquely equipped to detect (and succumb!) to bad air because their respiratory systems are so efficient. Here’s why.
Our lungs suck in air, exchange oxygen for carbon dioxide, and push it out. This is slightly inefficient because some air remains in our lungs after we exhale. If you’ve ever had “the wind knocked out of you” you know it feels awful to lose that residual air.
Human lungs and diaphragm (animation from BIO 378, Prof. Gary Ritchison, Eastern Kentucky University)
Birds’ lungs don’t expand and contract; they only perform the oxygen-CO2 exchange. Instead birds have 7 to 12 air sacs that act like bellows, moving air in and out of the lungs and the body. The air sacs (pink below) move air in only one direction through the lungs (dark blue below), pushing all of one breath out when the next one comes in. No residual air!
Bird respiratory system, air sacs highlighted (image from Wikimedia Commons)
Because the air sacs perform different functions, each air molecule takes 4 steps to pass through the bird’s body –> two in/out breaths.
1st Breath, Air molecule enters the bird.
1. Inhalation: Molecule is sucked into the body by the posterior (back of the bird) air sacs
2. Exhalation: Posterior air sac pushes molecule into bird’s lungs
2nd Breath, Air molecule leaves the bird.
3. Inhalation: Molecule is pulled out of the bird’s lungs by the anterior (front) air sacs
4. Exhalation: Anterior air sac pushes molecule out of the bird!
In this way, birds have more time to absorb oxygen from each breath and their bodies notice airborne poisons sooner than mammals do.
To put it all together, here’s a four and a half minute video that shows how it works.
One more amazing feat: The thin walls of birds’ air sacs can extend into the hollow bones of their wings and legs. They have extra places to store air!
(photo credits: Click on each image to see its original in context.
*Station Officer John Scott with canary cage used in coal mines rescue training at Cannock Chase, UK. Image courtesy of the Museum of Cannock Chase. Copyright unknown.
*Human lungs and diaphragm. Image linked from Bio 378, Lecture 10, Prof. Gary Ritchison, Eastern Kentucky University
*Bird respiratory system diagram from Wikimedia Commons.
*Video of bird respiration by Ammt Bio on YouTube)
At first the birds had no hierarchy and quietly assessed each others’ rank without fighting. After about a week the major rankings had shaken out and some of them started to fight.
For 24 days the humans kept track of the parakeets’ interactions, carefully noting who fought and who won. Interestingly, many birds didn’t fight and even those who did seemed to pick their battles.
Analysis of more than 2,300 interactions showed that the parakeets kept track of who won and lost and extrapolated the rankings to figure out their nearest competitors and those not worth challenging. They only bothered to fight if they were close in rank and couldn’t determine it by extrapolation. For example,
Able and Charlie know they’re both stronger than Baker (no fight necessary) so they must be roughly equal but don’t know who’s best unless they fight … except …
Dirk beat up Able yesterday and Charlie beat Dirk. By inference, this makes Charlie better than Able. After only two fights the pecking order is: Charlie > Dirk > Able > Baker.
This kind extrapolation involves a lot of math (logic) and is much harder to do in large groups but the birds are so smart that they avoid fights by doing the math in their heads.
Math comes in handy, even in social settings. There’s a good reason it’s taught in high school. 😉
p.p.s. Monk parakeets (also called Quaker parakeets) are “agricultural pests” in many states. In Pennsylvania they’re illegal to own and are removed when found in the wild. This is not the case in New York where monk parakeets hang out near JFK Airport, as shown in Gintarus Baltusis’ photo below.
Monk parakeets near JFK airport (photo by Gintaras Baltusis)
p.s. Click here to read more about the similarities between hummingbirds and swifts.
(hummingbird photo by Kate St. John, garden claw clip art from clipartbest.com, white-throated swifts illustration from the Crossley ID Guide for Eastern Birds, Creative Commons license, via Wikimedia Commons. Click on the images to see the originals)
Back in July at Cunkelman’s Neighborhood Nest Watch banding, Bob Mulvihill’s mist nests captured an immature blue-winged warbler (Vermivora cyanoptera). With the bird in hand he put his fingers lightly on the bird’s beak and it immediately opened its beak and pushed Bob’s fingers away. What an unusual talent! These warblers have extremely strong gaping muscles.
Golden-winged warblers, closely related to blue-wings, are so well studied that this fact is mentioned in the literature about them. Bob has also found it to be true of the (formerly*) Vermivora warblers and oriole species he’s banded in eastern North America.
Why this unusual talent? Vermivora literally means “worm eater” — vermi:worm, vora:eat. The “worms” are small caterpillars (not earthworms) that hide among leaves, often wrapped in cocoons or in curled up leaves. The warblers open the rolled leaves against the caterpillars’ will.
When you see these talented birds watch them probing among the leaves. They’re making a strong opening.
(photo by Kate St. John)
And what’s all this about formerly(*)?
The genus Vermivora used to contain nine species including Tennessee, orange-crowned, Nashville, Virginia’s, Colima and Lucy’s warblers, but in 2010 the American Ornithological Union transferred all but Bachman’s (extinct), blue-winged and golden-winged to the genus Oreothlypis. After years of having nine Vermivoras, it’s hard to keep up with the changes.
Male ruby-throated hummingbird in bander’s hand (bander Bob Mulvihill, photo by Kate St.John)
Now that the breeding season is over and dry weather is suppressing native flowers, ruby-throated hummingbirds are swarming to backyard feeders in Pennsylvania. All of them are small and feisty, but did you know the males are even smaller and more belligerent than the females?
Ruby-throated hummingbirds are sexually dimorphic in size though they’re all so tiny that only a bander could know. At banding, birds are weighed and measured and so we’ve learned that male ruby-throats are about 87% the size of females in wing length and weight(*). Their size is related to their lifestyle.
Female (or is this an immature?) ruby-throated hummingbird in bander’s hand (bander Bob Mulvihill, photo by Kate St.John)
Male hummingbirds are the original deadbeat dads. Ruby-throated males rush north in the spring to claim territories with lots of food which they vigorously defend with aerial displays, chasing, and bill-to-bill sword battles.
When a female shows up the male doesn’t welcome her at first (he acts annoyed) but he switches to intensive courtship displays when she perches. Good hovering technique really impresses her and to do it well he needs lots of energy, smaller wings, and a lighter body than hers — which he has.
As soon as he’s mated with one lady he looks for the next. He never helps with nesting and young and is so focused on attracting another female and warding off other males that he may forego feeding for much of the day. Banders have found that adult males lose weight in June and July, though they regain it in August.
By the end of the breeding season there are noticeably fewer adult males than females at bird banding stations. In a study done at Powdermill Nature Reserve, Bob Mulvihill and Bob Leberman found that the adult sex ratio is most skewed in the fall when there are 4.1 adult females for every 1 adult male.
Their paper(*), published in The Condor in 1992, describes why more adult males die in the summer than at other times of year:
“As a species, the Ruby-throated Hummingbird is near the extreme of small size that is physiologically possible for an endothermic vertebrate. It is conceivable that males approach a critical body mass during the summer. Below this critical mass they may have to abandon nocturnal homeothermy for hypothermic torpor, and may starve overnight or during periods of inclement weather.”
Male ruby-throated hummingbirds are so small and belligerent that it shortens their lives.
(photos taken at the Neighborhood Nestwatch bird banding at Marcy & Dan Cunkelman’s by Kate St. John, 18 July 2015. Bob Mulvihill is the bander holding the birds.)
(*) The paper by Robert S. Mulvihill and Robert C. Leberman is entitled A Possible Relationship Between Reversed Sexual Size Dimorphism and Reduced Male Survivorship in the Ruby-throated Hummingbird, published in The Condor 94: 480-489. It’s available as a PDF here at Sora. Their work is cited in the ruby-throated hummingbird account at Cornell’s Birds of North America.