Wind turbines and Birds

BIRD COLUMN FOR August 8, 2004

By Benjamin P. Burtt

Topic: Wind Turbines and Birds

Are these devices for generating electricity from the wind a danger to birds?

Provided below is a copy of all the material that appeared in the newspaper column on the date above, plus extra information for the interested reader who wishes to learn more about this subject.

Mr. Burtt: There are wind mills near Cazenovia, NY for making electricity. I've heard that they can somehow be harmful to birds? What can you tell me about this? J.G. Cazenovia

Dear J.G. The use of wind turbines to make electricity is attractive because it does not contaminate the air. Each tower has a three blade propeller that is turned by the wind. However, some people worry that many birds will be killed by flying into the moving blades.

This concern arose when it was reported that a number of hawks and eagles were killed at the Altamont Pass area east of San Francisco after wind turbines were first put there 20 years ago.

Bird Collisions with human-made structures.

This question brings up the whole subject of the structures we build and that birds are killed by flying into them each year.

Birds collide with our cars and trucks, with buildings and with the windows in them. Powerlines take their toll. Radio and television antenna towers and cell-phone towers on the tops of hills or ridges, cause fatalities in bad weather at night when birds are forced to fly nearer the ground during migration. They run into the towers or the guy-wires supporting them.

Dead birds have been counted and estimates have been made of the number of fatalities at these different structures per year. The estimates vary because scientists use different assumptions in making their calculations. In each case below, I have chosen the estimate that is half way between the lowest and the highest published estimate.

For example, birds die when they collide with a building, a house or its windows. About 4 die each year per building. I know that in a year, about 20 birds hit my big picture window as they mistake the reflection for part of the scenery. Most are able to fly away, but 4 or 5 die. Thus my house is about average.

Counting all the buildings and houses in the United States, about 400 million birds are killed each year by hitting buildings and windows. Buildings kill more birds than other structures.

Collisions with powerlines cause about 85 million deaths. This is about 175 per mile of wire.

Cars, trucks and buses kill about 70 million birds per year. That is a lot of birds, but taking into account the number of cars, on the average, it means that my car kills a bird every other year.

The TV and radio towers cause the death of about 20 million birds per year. Each tower kills about 300 per year. This happens most often when birds are migrating at night and bad weather and clouds force the birds to fly nearer the earth. A TV or radio tower mounted on a high point is thus a serious hazard and the guy wires take their toll. Steadily burning lights on the towers seem to attract the birds as well.

Wind turbines kill about 2 to 4 birds per tower per year depending on where the tower is placed and how it is constructed. About 45,000 birds are killed each year at turbines about the country. This knowledge comes from careful carcass counts at existing wind plants.

CAPTION: These modern turbines to produce electricity from the wind are in Wyoming. There are some 15,000 others around the U.S. including some in New York State. Note the size in comparison to the old fashioned windmill on the left.

The structure of the wind turbine and the tower

Those early turbines rotated so rapidly that the short, moving blades were almost invisible to birds.

The turbines then were supported by a lattice of supports and braces much like you see on the old fashioned windmill on the left in the photograph. Birds that perched there may have been killed as they tried to fly away through the whirling blades.
(Photo Courtesy of David P. Young Jr., West, Inc.)

At Altamount mentioned above, on the average one or two birds were killed per year at each tower, but with 6000 towers clustered there, the kill was impressive.

The improved models

The turbines near Cazenovia are modern ones like the white ones in the picture and are supported by a single tower with no place for birds to perch. The blades turn more slowly on these newer models and thus are visible as they turn. Nevertheless the tip of the blade is still moving fast enough to kill a bird.

The towers east of Cazenovia are 216 feet high and each of the blades is 108 feet long. The blades turn at about 20 revolutions per minute.

The location

Careful attention to the environment in the area of the wind turbines must be taken into account. The place chosen must have wind of course, but it should not be where there is a concentration of birds. The early wind turbine plants were located without attention to the use of the area by birds.

It turned out that there were lots of birds-of-prey in the area of the Altamount power plant in California that was mentioned above. Many rodents lived there and this brought the birds of prey in.

The modern turbines are probably less dangerous to birds, but much depends on where they are put. During migration, birds generally fly well above the towers if they are located on flat land. In the daylight, low flying birds are observed to swerve as they approach the tower.

However, if the towers are put on high ridges birds may hit them while migrating at night. An estimated 20 million birds are killed every year by collisions with TV and radio towers placed in such spots. Turbines located there would stick well up into the sky too.

At night, in bad weather, the clouds are sometimes very low. Since birds fly below this cloud ceiling, they may be forced to fly so low that they will run into any tall tower on the ridge.
Shown in the picture here is part of a line of turbines that runs along the top of a ridge of the Alllegheny Mountains in Pennsylvania. Often, as here, some of the forest along the top of the ridge is removed during construction. Cutting the forest for 10 miles along the ridge does destroy and fragment considerable nesting habitat for birds.

To prevent collisions with aircraft, the towers must have lights. If there are steady lights that are on all night or if the area around the base of the tower is illuminated, when birds are forced to fly low, they encounter the lights and are often confused. They circle the lights and hit the tower or its guy wires.

Photo Courtesy of D.D. Boone, Bowie, MD

Blinking red or white strobe lights do not cause a problem and all turbine towers now use them, but some older TV towers have steady white lights.

How dangerous are turbine towers?To answer this question for a particular location, a careful, scientific study must be made. This must be done nowadays in order to get a permit. The developer must engage the services of a company that has the knowledge and experience to do the scientific experiments required.

There are a number of companies in the environmental studies business. They are also hired by government agencies such as a state conservation department, the Fish and Wildlife Service, or a town to study the project and provide a report on the impact the project will have on the environment.

As for wind turbines and birds, the occurrence of birds at the site must be studied. Radar can be used during migration to determine the number of birds moving, their speed, the direction as well as the altitude at which they fly. Many birds migrate at night and radar is of particular use then.

It is useful to determine how many birds fly low enough to be at risk for colliding with a tower or the blades. In one study by radar of a prospective site in West Virginia. some 1,800,000 birds flew over the 10 mile stretch of the ridge of mountains during the fall migration of 2003.

The radar detected birds from the ridge top up to nearly a mile above it ( 4922 feet). The critical region was from the ridge up to a point just above the top of the prospective turbine blades. In that lower region of higher risk, 300,000 birds were observed during the fall migration.

Of those, about 500 would have been killed. This conclusion was based on carcass counts at another ridge line wind plant where 2.37 birds were killed per turbine during the fall season.

These carcass counts are carefully done. Since predators may pick up a carcass before it is counted, the investigator must plant some dead birds to see how fast they are cleaned up. A test must also be run to see how well the planted carcasses are found by those making the survey. The 2.37 birds per turbine came from such a study.

Studies of this type have been made all over the country and they lead to the figure of about 2 birds being killed per turbine per year in the west. Where turbines are located on the Appalachian ridges in the east, the number varies from 2 up to 4 per turbine per year. I have found no studies that show higher numbers killed anywhere in the United States.

These studies are complicated and are done in a scientific manner and I have read such reports and am impressed with how thorough they are. Well educated biologists and other scientists make up the personnel of the firms doing the study.

Some people express the opinion that the investigation may be biased in favor of the developer. If that happens just once, the environmental consultant company is out of business. The report is used by the developer and by the agency that has to approve the project. Money to pay for the project often comes from both sources.

Summary of bird loss due to collisionsThe figures here are the estimates of the number of birds killed per year by colliding with each of the various human structures discussed above.

400,000,000 by collisions with buildings and windows
85,000,000 by collisions with power lines.
70,000,000 by collisions with vehicles
20,000,000 by collisions with TV and radio towers
45,000 by collisions with the 15,000 wind turbines

If we eventually had a million turbines, they would account for only 1.5% of all the casualties that birds now undergo to live with we humans.

Just for comparison, the Audubon Society estimates that about
100,000,00 birds are killed by house cats each year.

Producing ElectricityWe make most of our electricity by burning coal or oil. This produces acid rain that damages our forests, kills fish in the lakes down wind and ultimately makes it impossible for some birds to feed in our lakes and streams.

The carbon dioxide and other gases from the furnaces and from our vehicles traps the heat of the sun and is slowly raising the temperature of the earth. ( This can change the climate and it is called the "greenhouse" effect.)

Electricity from wind turbines produces no toxic or harmful materials, but some birds and bats are killed by colliding with the towers.

So how do we weigh the benefits of having electricity with the harm its production causes to the environment? We do have to weigh the benefits and the risks. Becoming informed is the only way we can each reach an intelligent decision. I hope that this discussion has been of help to you.