As wind power spins forward in the United States — the five-turbine Block Island Wind Farm is the first offshore wind-energy facility in the country — the giant turbine blades that generate energy are often blamed for the death of birds and bats.

Turbines certainly do kill flying creatures, but how does this oft-maligned form of renewable energy stack up against other sources that are used to power our society? Plenty of research still needs to be conducted — especially concerning bat mortality caused by energy production — but most of the research already done shows fossil fuels are more lethal than spinning blades.

North American wind turbines kill an estimated 140,000 to 328,000 birds annually, according to a 2013 study. Another 2013 study claimed every year 573,000 birds and 888,000 bats are killed by wind turbines. A 2014 report claims turbines kill between 214,000 and 368,000 birds annually.

The peer-reviewed 2014 study by two federal scientists and the environmental consulting firm Western EcoSystems Technology Inc., however, found that number is small compared with the estimated 6.8 million fatalities from collisions with cell and radio towers. The study’s authors estimated that on an annual basis less than 0.1 percent of bird populations in North America die from collisions with turbines.

Collisions with windows, on the other hand, kill between 365 million and 988 million birds in the United States annually.

“Properly sited wind turbines are relatively bird friendly, especially when compared to fossil fuels,” according to the American Bird Conservancy (ABC). “However, they are far from benign.”

The Virginia-based organization has noted that wind turbines and their associated infrastructure, notably power lines and towers, are among the fastest-growing threats to birds and bats in the United States and Canada. At the end of 2016, there were more than 52,000 operating, commercial-scale, land-based wind turbines in the United States, according to the ABC, producing about 66,000 megawatts of power.

The Migratory Bird Treaty Act makes it illegal to kill any bird protected by the act, even if the death is incidental, such as being struck by a spinning turbine blade, killed during a mountaintop mining explosion, or suffocated in an oil spill. The Bald and Golden Eagle Protection Act recommends that to avoid eagle deaths companies should seriously consider where they site energy projects.

Wind-energy development, like all energy projects and infrastructure, can contribute to habitat loss, which can have significant impacts on birds, bats and other wildlife.

The ABC recommends “bird-smart” wind-energy development that ensures turbines are sited away from bird-collision risk areas; employs effective and tested mitigation to minimize bird fatalities; conducts independent, transparent, post-construction monitoring of bird and bat deaths; and calculates and provides fair compensation for the loss of ecologically important, federally protected birds.

Six decades ago hydroelectric power was celebrated as a source of renewable energy. Hydroelectric power includes both massive hydroelectric dams and the smaller mill dams that once powered the Industrial Revolution, most notably in New England. Now, many dams are being torn down because of their unintended environmental and wildlife impacts, such as changing ecosystems and impeding the path of migratory fish.

A bigger problem for birds and bats is the continued burning of fossil fuels. A 2014 National Audubon Society report noted that hundreds of bird species in the United States, such as bald eagles, are at “serious risk” because of climate change.

A 2009 study using U.S. and European data on bird deaths estimated the number of birds killed per unit of power generated by wind and fossil fuel sources. It concluded that wind facilities are responsible for between 0.3 and 0.4 fatalities per gigawatt-hour of electricity, while fossil fuel power power plants are responsible for 5.2 fatalities per gigawatt-hour.

Another study, published four years later, found that wind turbines kill 0.27 birds per gigawatt-hour, nuclear plants 0.6, and fossil fuel power plants 9.4.

Bat deaths attributed to wind turbines aren’t as well documented, but limited research has shown this renewable-energy source does have an impact. In Rhode Island, for instance, turbine owners have reported dead bats at the base of their structures.

Besides the dangers spinning blades pose for the only mammals that can fly, a 2011 study found that bats can succumb to the pressures created when turbine blades pass through the air, a phenomenon known as barotrauma.

While bats normally live for a long time, they, like sharks, are slow reproducers, meaning their populations rely on high adult survival rates.

All energy production comes with costs, especially to ecosystems and wildlife. Source and siting should be about making decisions based on more than just price and profit.