Look up into the air, and you will probably be able to see birds and, if lucky, some bats. However, there is wildlife so small you can’t even see it.
Bats are the only flying mammals, although some mammals can glide or soar. There are over 10,000 species of bird, most of which use wings to fly. There are over 1 million species of insects, although this is likely to be much more, and many spend most of their lives in the air.
In this article, we look at the wildlife that lives in the air.
The air not only provides a home for many creatures, but it also plays an important role in the lives of all earth-bound organisms. Its most visible role is as a massive storage of oxygen and carbon dioxide.
Variations in atmospheric pressure, temperature, and moisture content, as well as the constant movement of the air, all contribute to our weather and, as a result, have a significant impact on all animals.
The greatest winds occur when the pressure drops significantly before storms.
Winds can take up very enormous objects and transport them long distances before dropping them. There have even been tales of frog showers following severe gusts, but most of the objects carried are much smaller.
Dust is the most abundant inanimate item swept up by the wind and is frequently carried for considerable distances. Saharan red dust, for example, is periodically dropped over regions of Europe. Massive volumes of dust and smoke are added to the air by urban and industrial development, which can have a wide range of effects on plant and animal life.
Among the well-known effects of such pollution is the disappearance of lichens in and around cities and the rise of industrial melanism in moths and other insects.
Animals in the Air
Although many little animals, like dust and seeds, are lifted into the air, only three groups can truly fly: birds, bats, and insects, with the latter being the largest and providing the majority of food for the other two.
The aerial insects are divided into two groups: directional fliers, which fly fiercely and travel wherever they want regardless of wind direction, and weaker fliers, which, although actively flying, are carried along by the winds. This last category is known as aerial plankton.
Most directed fliers simply use the air as a transportation medium to get from one location to another, such as bees and butterflies that fly from flower to flower. However, some insects are entirely airborne.
Dragonflies, for example, can spend hours on the wing, hawking and capturing food in flight. Winter gnats and flies frequently dance up and down in the air, particularly on a winter afternoon. These insects are almost all males, and the dancing swarms aim to attract females.
Flies, chalcids, and other small hymenoptérans, aphids, and thrips are among the insects moving in the wind. Occasionally, there are massive ‘explosions’ of these insects, particularly aphids and thrips, when large numbers mature and take to the air in exodus flights designed to transport them to new homes.
In July 1979, for example, swarms of the rose-grain aphid infested considerable regions of the United Kingdom. Conditions had been favorable for the development of this species earlier in the year, and adults were so plentiful in late July that work had to be halted in certain factories and dockyards.
According to radar and suction trap data, almost 200,000 tons of these insects were in the air just over south-east England at the end of July—roughly a thousand million aphids. Many were taken out to sea, only to be hauled back as the winds shifted, and they were also caught more than a mile up in the air.
Nets pulled behind planes and strung beneath high-flying kites have gathered insects at heights of more than 15,240m (50,000ft), however, the vast majority of aerial plankton occurs in the first 90m (300ft), with a rapid decline in numbers as the height climbs. Traps 3m (often) above ground grabbed 540 insects in 10 hours, whereas comparable traps above 90m (300ft) caught only 80.
Numbers also change with temperature, rising to around 21 C (70 F) and then declining again. The most planktonic species are found aloft during the day, with an almost total drop-off at night. Summer days have noticeably more insects in the air than winter days.
However, flying insects are not the sole type of aerial plankton. Many wingless insects, including several little hairy caterpillars, are whisked up by the wind and scattered across a large region in this manner. Some have been discovered at 610m (2000ft). Spiders are also plentiful in the air, mainly as juveniles who use silk threads as parachutes to fly to fresh pastures.
Bats and Birds
Aside from the previously mentioned unusual swarms of insects, it has been calculated that up to 25,000,000 insects may be in the air across 2.6 square kilometers (l square mile) of the countryside at any given moment. Fewer are seen in cities, but their numbers are still significant. These insects provide a massive food source for swifts, swallows, and martins, all of which catch their meal in the air. These birds appear to fly higher in warm weather when the insects are higher up.
Although most airborne plankton settles at night, many larger insects, such as moths and beetles, are on the flight. They are the primary meal of nightjars and bats, which replace swifts and swallows when evening sets.
Birds, of course, are the masters of the sky. There are over 10,000 species of birds. Most of them fly below 150m (500ft), although radar echoes have revealed that migrating birds such as dunlin can fly as high as 7000m (23,000ft), while whooper swans can migrate at heights of up to 8000m (26,000ft).
Swifts fly far higher than martins and swallows and can soar to 3050m (10,000ft) at night to roost on the wing. In contrast to the heights attained by birds, bats spend the majority of their lives no higher than 60m (200ft).
The light bodies and feathers of birds, as well as the broad, leathery wings of bats and the gauzy, insubstantial wings of insects, are specifically equipped to maintain them in the air—the world’s biggest single habitat.
There are about 1,400 species of bats worldwide, ranging from the largest flying foxes to the smallest, Kitti’s hog-nosed bat. They are excellent at flying and many feed on the abundant insects flying at night.
Bats can be found roosting in caves, rock crevices, old buildings, bridges, mines, and trees. Bats can be found almost worldwide except in the arctic regions and extremely hot deserts.
Many species rely on the wind to carry themselves or their reproductive bodies from one location to another. The air is constantly packed with spores of bacteria, fungus, and viruses. These are too small to see when scattered in the air, but leaving some damp bread out for a day or two can reveal how many spores are floating around in the air.
Fern spores and pollen grains contribute to the airborne living dust. Conifers and blooming plants disperse pollen grains, which fertilize the female sections of the flowers and trigger seed production.
During the flowering season of wind-pollinated species, it has been projected that over a million grains of pollen may fall on each square meter of vegetation. A single birch catkin produces roughly 5.5 million pollen grains, whereas a single rye floret produces over 50,000.
Hazel, birch, alder, poplar, oak, and many more trees are wind-pollinated. They normally bloom early in the year, before the leaves have fully opened; otherwise, the leaves would trap too much pollen.
However, most pollen is released into the air in June and July, when grasses bloom, giving hay fever patients significant suffering. Although grass pollen is by far the most plentiful and vital throughout the summer, other wind-pollinated herbs, particularly plantains and nettles, add to the pollen count.
Parachutes for plants
Most seed-bearing plants have methods for dispersing their fruits and seeds far away from their parents, which is necessary if the species is to colonize new areas. The wind is a major dispersal agent and many plants have winged or plumed fruits that the air can carry away. Winged fruits of elm, ash, and sycamore are well-known examples. Even in calm conditions, these glide to the ground some distance from the parent trees, and they can travel for kilometers in severe winds.
Plumed fruits include parachutes of dandelions and related hybrid species. Willowherbs, like other plants, produce clouds of light, fluffy seeds that can travel great distances and have been spotted hundreds of feet in the air. Wings and plumes, however, are not required for wind dispersal, and many plants can distribute themselves simply by releasing little, light seeds that are easily swept up in gusts of wind.