why do birds fly high

Some birds fly at particular heights to minimise energy expenditure. For example, griffon vultures soar very high on rising thermals, while petrels and albatrosses travel very low to take advantage of the uplift created by waves (one griffon vulture was recorded at an impressive 10,973 meters altitude)

The highest flying bird is the Rüppells vulture. Over West Africa on November 29, 1973, a commercial aircraft struck a bird at 11,300 meters. It was identified by feathers stuck in the engine as a Rüppells vulture, a severely endangered species whose blood has been found to contain a type of haemoglobin that binds oxygen incredibly well. Even with the ability to use radio- and satellite-tags to track flight paths in detail, this record has remained unbroken.

Many small migrants travel long distances at a steady altitude, ascending from 1,000 to 6,000 meters. When their cruising speed and power start to diminish, this enables them to take advantage of the thinner air, which is easier to travel through.

There are several reasons why birds fly at certain heights. Wing-feeding species select an altitude where their preferred prey is most plentiful. Thus, house martins descend to catch aphids and midges, swallows hunt relatively low to catch larger flies, and swifts dive even lower to catch the tiniest invertebrates.

The travelers are unaffected by the low oxygen levels because they can effectively remove it from the air, and they are also unaffected by the cold because their active flight muscles produce a lot of heat.

How High and How Fast Do Birds Fly? In general, birds fly in accordance with the teasing advice that pilots frequently receive: “fly low and slow.” The average cruise speed is between 20 and 30 mph, and the fastest accurately recorded air speed is about 47 mph for an eider duck. But during a chase, things pick up speed. Ducks, for instance, can fly 60 mph or more, and reports suggest that a Peregrine Falcon can reach 200 mph (though 100 mph may be more typical). It’s interesting to note that a bird’s speed and size don’t really correlate. The maximum speeds that geese and hummingbirds can travel are comparable. Naturally, there is a significant difference between a bird’s maximum speed and its typical flying speed. One might anticipate that when the bird is “around home,” it will either minimize its metabolic rate—that is, use less energy per unit of time—or maximize the distance it travels for each unit of energy used. Similar to an observation aircraft pilot, a vulture searching for prey might maximize endurance, and a seabird flying to far-off feeding grounds might maximize range, akin to a Concorde facing headwinds during a transoceanic flight. Staying up longest does not necessarily mean going farthest. A bird’s maximum endurance in the air is six hours at 15 mph, or 90 miles, or five hours at 20 mph, or 100 miles, maximum range. As they race to defend a territory or are being pursued by a predator, birds can also opt to fly as fast as possible. Or they can choose some compromise between speed and range. Gary Schnell and Jenna Hellack of the University of Oklahoma measured the ground speeds of a dozen species of seabirds (gulls, terns, and a skimmer) close to their colony using Doppler radar, a tool akin to that used by police to apprehend speeders, in order to ascertain what the birds typically did. They also used an anemometer to measure the wind speed, which they then used to calculate the birds’ airspeeds. (Since surface friction slows air movements near the ground, some estimation errors resulted from measuring wind speeds generally closer to the ground than the birds did.) The majority of airspeeds were observed to be between 10 and 40 mph. It was possible to determine each bird’s power requirements at each speed, and using that data, it was determined that the birds were typically compromising between increasing their range and lowering their metabolic rates, with a greater focus on the former. Although airspeeds varied greatly, significant variations in airspeed did not necessitate sharp increases in energy consumption when the airspeed was close to the minimum metabolic rate. For instance, a gull that could fly at any speed between 15 and 28 mph without increasing its metabolic rate by more than 15 percent would be able to maintain its most efficient loiter airspeed of 22 mph. Most birds fly below 500 feet except during migration. There is no need to use the energy to go higher, and doing so could put you in danger from things like exposure to stronger winds or hawks’ keen vision. However, birds frequently soar to relatively high altitudes during migration, perhaps to evade dehydration in the warmer air near the ground. In the Caribbean, migratory birds are typically seen at elevations of 10,000 feet, though some are found at elevations of half or even twice that. Long-distance migrants typically begin their journey at 5,000 feet and gradually ascend to 20,000 feet. Similar to jet aircraft, migrants’ ideal cruise altitude rises as their “fuel” runs out and their weight decreases. In order to search wider areas for food and to observe the behavior of distant vultures for clues as to the location of a feast, vultures will occasionally soar above 10,000 feet. An airline pilot visually identified a flock of Whooper Swans at 29,000 feet after they were spotted on radar arriving over Northern Ireland during their migration, which is arguably the most impressive altitude record. Since bird lungs can extract a larger fraction of oxygen from the air than can mammal lungs, birds are able to fly at altitudes that would be impossible for bats to reach. SEE: Flight and Wing Shapes; Soaring; Vee Formation Flight; Flight Adaptations Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.

FAQ

What does it mean when birds fly really high?

Birds flying high in the sky usually indicate fair weather. As the adage goes … Hawks flying high means a clear sky.

Why do flying birds appear higher?

When we perceive the bird, light beams from the bird’s body travel from a rarer to a denser medium, bending toward the normal. This refraction of light causes the bird to appear flying higher in the air in contrast to what we see in reality.

Why do birds fly at a certain height?

During migratory flights, birds select flight altitudes that minimize energy expenditure via selection of advantageous tail- and cross-winds.

How do birds decide how high to fly?

Species that feed on the wing choose an elevation at which their preferred prey is most abundant. So swallows hunt fairly low to take larger flies; house martins go higher to seize aphids and midges; and swifts zoom around higher still to pursue the smallest invertebrates.