Flying insects “bug” us when birding, but they are BIRD FOOD!

When you watch swallows flying over a field, what do you see? I see graceful birds performing amazing acrobatics in an empty sky! But they are actually feeding in a habitat filled with flying insects that aren’t visible to us.

Swallows, swifts, nightjars, flycatchers, martins, kingbirds, peewees, and nighthawks are all aerial insectivores – that is, they feed on the wing by capturing flying insect prey. The birds that feed by hawking (remaining airborne to feed and eat) divide the sky just like birds do in forests. Swifts and nighthawks feed in the upper air spaces. Purple Martins take the mid space. Tree Swallows stay nearer to the ground. Birds that sally (foraging from and returning to a perch) also feed at different levels. Great Created Flycatchers feed at a higher level than Eastern Phoebes, which feed close to the ground.

The sky is a habitat just like an ocean. Birds feed at different elevations because flying insect species vary by height, time of day, time of year, and weather. We think of insects near the ground, but insects fly to migrate, expand their colonies, and feed on other insects.

In researching this article, it was hard not to feel a little despair. Aerial bird species, particularly those in Canada and the Northeast US, are in steep decline. The flying insect species they feed on are similarly declining, but there have been few long- term studies of flying insects, so scientists don’t know the extent of insect decline or the connection with birds. In 2017 there was a German report of a 75% decrease in flying insects where they have been monitoring flying insects at protected natural sites for 27 years. Neonicotinoid pesticides, being used in adjacent agricultural fields, are a top suspect for the decline.

Aeroecology, a new field of study looking at the ecology of life in the air, will hopefully provide some answers. In additional to natural inhabitants like birds, bats, and arthropods, this field incorporates manmade structures (buildings and cell towers) and human altered landscapes (urbanization and intensive agriculture).

I was surprised to learn that aerial bird feeders are selective with the insects they feed on, particularly during nesting. Insects may not have nutrition labels, but flying insects with aquatic larvae have higher omega-3s than those that are terrestrial. One study demonstrated the better health of chicks raised on such a diet over one of completely terrestrial insects. This research suggests protection of freshwater wetland habitat may be important for the long-term success of aerial bird reproduction. Aquatic larval insects include mayflies, odonates, caddisflies, mosquitos, and crane flies.
Let’s dive into examples of a few aerial bird food families.

This Callibaetis sp female imago finds a safe location to wait for days until her eggs mature

This Callibaetis sp female imago finds a safe location to wait for days until her eggs mature

Mayflies are dinosaur-age insects. Their aquatic larvae live in freshwater lakes and rivers. They uniquely have a winged immature phase (subimago, or dun to fishermen). As adults (imagos), they have a short life with a sole purpose to mate—they don’t even have a mouth. A single species (there are about 600 in North America) typically synchronize their hatch and can form swarms big enough to be detected by radar. For aerial bird predators, it’s time for a feast!

There have been alarming reductions in some mayfly populations in the past decade. Theories for the decline include neonicotinoid pesticides, algae blooms from fertilizer runoff, and increased water temperatures from global warming. Mayfly eggs are sensitive to pollution, serving as a “canary in a coal mine.”

This female Blue Dasher is a common dragonfly in Pennsylvania that supports the success of Purple Martin colonies.

This female Blue Dasher is a common dragonfly in Pennsylvania that supports the success of Purple Martin colonies.

Odonates, the dragonflies and damselflies, are themselves aerial insectivores. I saw an Ebony Jewelwing this year eating a mayfly! Dragonflies are such skilled and acrobatic fliers that it’s amazing any bird can capture one. They can turn in an instant, fly backwards and upside down, hover in place, and achieve speeds of 22-34 mph. This agility is enabled by their ability to independently control forewings and hindwings (as insects they have 4 wings).

That kind of skill wouldn’t matter without the ability to see in all directions – which they can do! Each compound eye is made up of 30,000 eyes that serve as a type of 360° motion detector.

In the sky, this winged woolly aphid looks like a floating fairy.

In the sky, this winged woolly aphid looks like a floating fairy.

Aphids, yes, the little plant-sucking insects on the stems of plants and flowers, are eaten by aerial insectivores. Did you ever wonder how aphids just appear on plants? Well, they asexually reproduce winged offspring that fly off to colonize new plants and locations. Aphids are poor, weak fliers that often drift in the wind. Aphids have been found at 2000 feet.

Winged ants look like wasps, but are harmless. Ants have a bend or elbow in the antenna.

Winged ants look like wasps, but are harmless. Ants have a bend or elbow in the antenna.

Ants are a fascinating social insect that live in colonies. When a colony is successful, the queen will produce (and workers support) fertile males and virgin queens called “alates” to find their own mates and start new colonies. The winged alates leave the colony on the same day in a “nuptial flight”. I have witnessed a few of these fascinating events in my yard. The alates are escorted by workers up vegetation where they lift off. This can create a swarm that attracts predators. Over many years, a large colony can generate thousands of alates, but only one or a few will ever succeed to start a new colony. The fate of many is as food. Otherwise, ants might take over the world!

Karen Campbell, who shares her work on FocusOnNatives.com and is a Lehigh Valley Audubon board member, provided the content and images for this article.