6 million years ago, in the late Miocene, there lived on Earth a behemoth in the air, weighing up to 70 kilograms and reaching a wingspan of up to 7 meters.
Like a light aircraft that can catch 36 pounds of prey, what evidence of their existence?
Biologists have found fossils of these giant creatures in both the Angus Mountains and the vast Pampas Prairie, and have pieced together their general appearance.
They are known as the Argentine giant eagle, which was not extinct until 250,000 years ago, and is believed to be the ancestor of the modern large bird of prey stork and bald eagle, the only thing that puzzles scientists is how such a bulky body can fly in the air.
We need to look for answers to this question from the large birds of prey that live in the region today, especially the condor, which is closely related to the Argentine giant eagle.
The birds that fly in the sky are now much smaller than they were before history, and one of the heaviest flying birds in the world: the Andean condor, weighs 32 pounds.
Although it is not worth mentioning compared with its ancestors, with the current energy supply of the biosphere on Earth, scientists still think that it is a miracle that bald eagles can fly and fly so well.
Because once a bird grows so big, each flapping of its wings consumes a lot of energy, and the researchers estimate that birds like bald eagles use 30 times more energy when flapping their wings than they do at rest.
So a bird of this size who wants to fly by flapping its wings is undoubtedly as tired as a mammal running and sprinting on land.
It is estimated that flying a few hundred meters, a few kilometers, will take a break for an hour. It's not as convenient as being a land animal. So scientists believe that bald eagles mainly rely on rising air currents to glide.
But if you ask any expert on birds, how many times does a vulture flap its wings during each flight? Will changing environments and different weather conditions change their flight costs (energy consumption)?
No one can answer this question. But it wasn't until recently, when researchers used modern technology to monitor the flight of bald eagles in the air, that the puzzle was solved.
An expert in birds at the University of Swansea has developed a high-tech "flight recorder" specifically for bald eagles that can be mounted on bald eagles to record flapping their wings each time they search for food.
The study was conducted over a five-year period and the findings were published in the journal PNAS on July 13, 2020.
It takes a very long time and patience to catch a vulture and install the recording instrument. The research team specifically prevented some animal remains and bones that bald eagles liked in the Patagonian steppe.
Then wait for the vulture to take the bait, sometimes for days. But it turned out that it was easy to install the instrument, but it was very difficult to get the recording instrument back.
The instrument can record 320 different data points per second, the amount of data is very large, because the place where the vultures are active is in remote mountainous areas, there is no signal here, it cannot be transmitted, so it can only be recovered for research.
So the researchers designed a special system on the monitoring instrument, which will automatically fall off the bald eagle after a period of time, and then find the monitoring instrument according to gps positioning.
However, the search was difficult because Patagonia had almost no roads, and in order to get close to the vultures' habitat, the expedition team had to walk tens of kilometers, ride on horseback, use crampons and tie them together with ropes to cross the river.
And not every instrument can be found, and sometimes only one out of 8 instruments can be found.
To make it easier to access the habitat of bald eagles, the researchers chose targets young bald eagles, which prefer to congregate together and inhabit the gently undulating hills of the grassland.
Older vultures, on the other hand, choose to inhabit the high and inaccessible Andes Mountains.
The results of the study showed that young bald eagles flew an average of 3 hours a day, but flapped their wings for less than 2 minutes throughout the flight, accounting for only 1% of the flight time.
There was even a vulture that flew in the air for more than 5 hours without flapping its wings, flying a distance of 172 kilometers. What surprised the researchers most was that the number of times these vultures flapped barely changed whether they flew over the Andes mountains or over the prairies, and whether it was windy or not.
Flapping wings occurs mainly during take-offs and imminent unexpected landings, as well as when the rising air heat flow is weak, and other times the vulture can step on these rising heat streams and hover in the air all the time.
The findings also show that even under the weak heat conditions that can occur in winter, bald eagles only have about 2 seconds to flap their wings per kilometer.
The extremely low energy consumption during this flight is similar to that of an albatross. In fact, albatrosses seem to flap their wings more often than vultures (between 1% and 15% of the flight time after takeoff) and we don't yet know the overall energy consumption of albatrosses when flying.
It should also be noted here that all the birds studied were immature juveniles. There is evidence that birds' ability to fly improves with age.
This suggests that even young condors may invest very little energy in flight. Experienced veterans will flap their wings less often.
Judging from the entire flight time and the time of flapping its wings, we can even say that this bird can fly without flapping its wings.
By today's standards, bald eagles were very large, but 6 million years ago, the Argentine giant eagle, which had twice the wingspan of the bald eagle, dominated the Argentine sky.
It has long been believed that the Argentine giant eagle, an aerial giant beast, can use the air current to fly without flapping its wings. New data from bald eagles now support this hypothesis and show that terrestrial birds don't need much energy to fly very long distances.
In general, we think that large aircraft cost the most when they take off. In a new study of bald eagles, 75 percent of the wing flapping observed during foraging flights was associated with takeoff.
And the energy consumed in a 50-minute flight is comparable to the energy spent in 3.3 minutes at takeoff.
This underscores the importance of when and where vultures land, and they generally land in places with high drops and large updrafts. If you land wrong, you'll have to walk a long way to find a place like this to take off again.
When flying, the vulture looks agile, like a giant beast hovering in the air that will attack at any time. But on land, vultures are very clumsy.
Their huge bodies mean that they are difficult and expensive to take off. Once lifted off, these giant birds "zero consumption" fly in the air for hours.
Thesis Link:
pnas.org/content/early/2020/07/09/1907360117