Pigeon head-bobbing → motion parallax → astronomical parallax → distances to nearby stars → calibration of Cepheid variable stars → distances to nearby galaxies → compare galaxy distance with spectral redshift → Hubble–Lemaître law → Hubble constant.
Today, let’s talk pigeon head-bobbing. But first:
I’m surprised I didn’t know this. Wasn’t this the whole point of Soylent Green?
WLBOTT’s Official Pigeon
The Mourning dove is the official pigeon of the World’s Largest Ball of Twine Tour.
Why did we chose the mourning dove? Many mourning doves visit WLBOTT HQ, makes a sound of gentle existential disappointment (similar to our unpaid interns), walks around bobbing its head in the service of astronomy, and possesses the general demeanor of a bird that has just received an unsettling memo from Bev. The mourning dove also brings a suburban dignity to endless asphalt and barking dogs.
What’s the Deal with the Bobbing?
Some animals also use motion parallax, in which the animal (or just its head) moves to gain different viewpoints. For example, pigeons (whose eyes do not have overlapping fields of view and thus cannot use stereopsis) bob their heads up and down to see depth.
There are a few theories why some birds bob their heads when they walk. It could be that the behavior assists with balance, provides depth perception or sharpens their vision. The prevailing theory, however, is that birds in motion bob their heads to stabilize their visual surroundings. In comparison, we rely more on our eye movements, not our head movements, to catch and hold images while in motion.
Picture a pigeon on a moving treadmill. What do you think would happen as the pigeon walks with the speed of the treadmill and its environment remains relatively the same? Dr. Barrie J Frost (1978) did this experiment and the pigeon’s head did not bob.
The mourning dove (Zenaida macroura) is a member of the dove family, Columbidae. The bird is also known as the American mourning dove, the rain dove, and colloquially as the turtle dove, and it was once known as the Carolina pigeon and Carolina turtledove. It is one of the most abundant and widespread North American birds[.] Its ability to sustain its population under such pressure [hunting] is due to its prolific breeding; in warm areas, one pair may raise up to six broods of two young each in a single year. The wings make an unusual whistling sound upon take-off and landing, a form of sonation. The bird is a strong flier, capable of speeds up to 88 km/h (55 mph).
The species is generally monogamous, with two squabs (young) per brood. Both parents incubate and care for the young. Mourning doves eat almost exclusively seeds, but the young are fed crop milk by their parents.
Vocalization This species’ call is a distinctive, plaintive cooOOoo-wooo-woo-woooo, uttered by males to attract females, and it may be mistaken for the call of an owl at first. During the call, the throat of the dove swells. Close up, a grating or throat-rattling sound may be heard preceding the first coo. Other sounds include a nested call (cooOOoo) by paired males to attract their female mates to the nest sites, a greeting call (a soft ork) by males upon rejoining their mates, and an alarm call (a short roo-oo) by either a male or female when threatened.
Courtship begins with a noisy flight by the male, followed by a graceful, circular glide with outstretched wings and head down. After landing, the male will approach the female with a puffed-out breast, bobbing head, and loud calls[1]. Mated pairs will often preen each other’s feathers.
The male then leads the female to potential nest sites, and the female will choose one. The female dove builds the nest. The male will fly about, gather material, and bring it to her. The male will stand on the female’s back and give the material to the female, who then builds it into the nest. The nest is constructed of twigs, conifer needles, or grass blades, and is of flimsy construction. Mourning doves will sometimes requisition the unused nests of other mourning doves, other birds, or arboreal mammals such as squirrels.
The clutch size is almost always two eggs. Occasionally, a female will lay her eggs in the nest of another pair, leading to three or four eggs in the nest. The eggs are white, 0.22 US fl oz, 1.01–1.17 in long, 0.81–0.91 in wide, 0.21–0.25 oz at laying (5–6% of female body mass). Both sexes incubate, the male from morning to afternoon, and the female the rest of the day and at night. Mourning doves are devoted parents; nests are rarely left unattended by the adults.
[1] This vocalization appears in a WLBOTT standard, Faded Love….
"Faded Love" was written by Bob Wills, his father John Wills, and his brother Billy Jack Wills
As I look at the letters that you wrote to me It's you that I am thinking of As I read the lines that to me were so sweet I remember our faded love
I miss you, darling, more and more every day As Heaven would miss the stars above With every heartbeat I still think of you And remember our faded love
I think of the past and all the pleasures we had As I watch the mating of the doves[2] It was in the springtime that you said goodbye I remember our faded love
[2] In retrospect, this is an odd line. If you were to substitute, say, giraffes for doves, the imagery would change dramatically. Here is our lovelorn cowboy:
He doesn’t realize how many young lasses he has unintentionally perplexed and bewildered with the dove imagery. He has left a string of (mostly) broken hearts all across the panhandle.
Perhaps we should go with Una Paloma Blanca (The White Dove).
The song “Una Paloma Blanca” was written by Dutch musician George Baker, whose real name is Johannes Bouwens
When the sun shines on the mountain And the night is on the run It's a new day / It's a new way And I fly up to the sun
I can feel the morning sunlight I can smell the new-mown hay I can hear God's voice is calling For my golden sky light way
Una paloma blanca I'm just a bird in the sky Una paloma blanca Over the mountains I fly No one can take my freedom away
Once I had my share of losing For they locked me on a chain Yes they tried to break my power Oh I still can feel the pain
Predator Vs. Prey
Eye position Some animals – usually prey – have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. Examples include rabbits, buffalo, and antelopes. In such animals, the eyes often move independently to increase the field of view. Even without moving their eyes, some birds have a 360-degree field of view. Some other animals – usually predators – have their two eyes positioned on the front of their heads, thereby allowing for binocular vision and reducing their field of view in favor of stereopsis. However, front-facing eyes are a highly evolved trait in vertebrates, and there are only three extant groups of vertebrates with truly forward-facing eyes: primates, carnivorous mammals, and birds of prey.
By Fieldofview01.png: The original uploader was Jimfbleak at English Wikipedia. / derivative work: McSush – Fieldofview01.pngBased on: SPARKS, John, 1970. Owls; their natural and unnatural history. New York: Taplinger Pub. Co. Dostupné online. ISBN 0-8008-6170-1. Page 15., Public Domain, https://commons.wikimedia.org/w/index.php?curid=8843740
Some predatory animals, particularly large ones such as sperm whales and killer whales, have their two eyes positioned on opposite sides of their heads, although it is possible they have some binocular visual field. Other animals that are not necessarily predators, such as fruit bats and a number of primates, also have forward-facing eyes. These are usually animals that need fine depth discrimination/perception; for instance, binocular vision improves the ability to pick a chosen fruit or to find and grasp a particular branch. In animals with forward-facing eyes, the eyes usually move together.
