Why are birds flying so low to the ground?

Introduction

It’s low tide and a calm sea early in the morning as a flock of brown pelicans dips low and glides just above the surface of the Atlantic Ocean. The appearance may be graceful, but the real grace is efficiency. These birds are using tricks of physics to catch a nearly free ride over the deep.

The Strategy

Pelicans, skimmers, and other birds save energy when gliding across water because of something called the “ground effect,” which increases lift and reduces drag.

Video: Pelicans gliding over the ocean

These pelicans are gliding low and taking advantage of ground effect.

When a bird glides, it stretches its wings outward and rides the wind, saving the energy it would otherwise use to flap. In this “fixed-wing” mode of flight, some of the air that flows under the wing impacts it and washes downward, pushing the wing (and bird) upward. In addition, the curvature of the wing causes the air above it to move faster and drop in pressure, also contributing to the lift. Near the tips of the wings, the higher-pressure air below is able to push up into the region of lower pressure above and create swirling vortices. Both downwash and the vortices increase drag, adding to the amount of energy required to stay airborne.

When birds fly just above the water, the relative effects of these forces change. Because there is less room for downwash to disperse, it compresses the air between the wing and the surface, creating a cushion of even higher pressure that increases lift. There is also less space for vortices to form, decreasing drag.

Image: Gretchen Hooker / Biomimicry Institute / Copyright © - All rights reserved

As a pelican nears the water surface, the downwash below the wing compresses the air and creates a cushion of higher-pressure air (yellow arrows). This results in more lift (red arrows). The water also partially blocks the formation of vortices, and decreases drag.

The Potential

Studying methods that birds use to save energy flying can lead to innovations that help airplanes fly more efficiently, reducing fuel consumption and greenhouse gas emissions. Flying drones that survey and study waterways might be designed to glide close to the water to optimize energy and cover farther distances. And in the rising development of electric airplanes, it’s going to be particularly helpful to save as much energy as possible to help battery charges last as long as possible.

Download Strategy PDF

Related Strategies

Biological Strategy

How Flying Squirrels Control Their Glide

Flying squirrels

Flying squirrels have membranes and cartilage that help them change lift and drag forces, enabling them to glide more than 100 times their body length.

Biological Strategy

Why Fish Scales Aren’t Such a Drag

Fish

The shape of scales causes water flow to streak across fish skin, reducing turbulence and minimizing drag.

Biological Strategy

Skin Aids Gliding

Gliding possums

Membranes of skin between the wrists and ankles enable gliding possums to travel farther by increasing lift and reducing drag.

In the United States, between 49 million and 340 million birds die from collisions with cars every year. This happens for many different reasons.

For the most part, birds fly in front of cars by accident. That’s because they tend to fly low to the ground to catch insects and avoid predators. Since cars move so fast, birds sometimes don’t realize they’re in danger. In some cases, birds will react defensively to cars entering their territory.

Table of Contents

Birds Don’t Fly Into Cars on Purpose

Generally, birds don’t fly in front of cars on purpose.

Birds fly into cars because cars interrupt their natural flight path, and the cars just move too quickly for the birds to successfully dodge them.

Only very occasionally do they fly in front of cars intentionally.

Bird-vehicle collisions also happen due to the way that birds see. Birds have eyes on either side of their heads, rather than two in the front like we have.

This makes it harder for them to perceive depth, making it more difficult to gauge how far away an object is.

Pair this with clear glass windows and a fast-moving car, and you have a recipe for a collision.

Why Birds Fly Into Windshields and Windows

Birds may fly into cars because they have a hard time distinguishing glass from an open route.

This is the same reason why they also often on buildings; they simply don’t understand that the reflection they’re seeing isn’t real. 

Birds aren’t accustomed to glass because it doesn’t exist in nature, and they don’t know to look for visual cues like mullions or cracks in the glass.

They also perceive color differently than mammals do, reading visual cues as more brightly colored.

This makes reflections seem more realistic to birds, so they’re more likely to fly into the glass, thinking it’s open air.

Why Birds Fly Low to the Ground

Birds flight paths’ are low to the ground, in the same vicinity as cars, for several reasons.

One major reason is that flying higher in the air puts them in raptor territory, and many small birds are preyed upon by raptors.

Flying higher to avoid cars and other traffic also takes more energy, which birds prefer to conserve where possible. 

Large birds fly low to the ground when they’re looking for prey or when they’re scavenging food sources on the ground.

For example, vultures may fly close to cars if there is roadkill by the side of the road. 

Why Birds Sometimes Fly Into Cars on Purpose

Evidence suggests that birds swooping in front of cars are trying to defend their territory from the threat.

Cars move quickly and are foreign, so they may come across as predators. This is likely if you see a bird darting at a car, flying into the front of the vehicle, or circling it.

How To Avoid Hitting Birds With Your Car

To avoid hitting birds with your car, ensure you slow down while driving, especially if you see one coming across your path.

You can also use windshield reflectors when you’re parked to prevent them from flying into your windows and windshield.

The MCBUTY Windshield Sun Shade, available on Amazon.com, has dual benefits, protecting birds from hitting your car due to its reflective surface and preventing your car from heating up in the sun.

You can also avoid driving in areas where birds are present in wild numbers, or at least by driving more slowly when you know you’re near bird habitat.

This is an effective way to prevent a large number of collisions.

The Urban Bird Foundation works to reduce the risk of vehicle-bird collisions by educating drivers about bird habitat areas and advocating for solutions like wildlife underpasses and diversion poles.

It also monitors roads with high collision rates to identify problems and evaluate which solutions are most effective.

Warning signs instructing drivers that they’re driving through bird habitat lead to lower speeds and a lower risk of collisions with birds. 

Diversion poles and wildlife underpasses prevent birds from walking or flying in front of cars to pass the highway.

These poles provide a barrier to keep birds from moving across the road, and underpasses provide an avenue for them to cross safely. 

You should avoid tossing food waste out of your car windows if you want to prevent collisions with birds. This can attract rodents, which in turn attract birds of prey.

What To Do if You Hit a Bird With Your Car

If you hit a bird with your car, there’s a good chance it won’t survive the collision. However, you can call a wildlife rehabilitation specialist to check the bird to be sure.

There are also some things you can do to take care of the bird while you’re waiting for help. 

If the bird emerges from the collision still able to perch on a branch, you should leave it alone, as it can survive and recover on its own.

However, if the bird has a major wound or broken bones, it’ll need immediate medical attention to survive without needing surgery later. 

While waiting for help, keep the bird in a dark, quiet place at a comfortable temperature. A shoebox works well.

This will keep the injured safe from predators while you’re waiting for care, and it’ll keep the bird warm if you rescue the bird during the winter. 

If you open the shoebox and the bird flies away, let it go; this means it has recovered well enough to continue without medical care.

However, if the bird is dead when you find it, move it out of the way while wearing gloves and let it naturally decompose.

In no case should you attempt to keep the bird or its feathers if it’s a bird protected by the Migratory Bird Treaty Act.

This act prevents the possession of migratory birds or their parts if they’re native to the United States.

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