By the time the leaves begin to turn, Ontario wind farms are already deep inside their most dangerous season for bats, and the calm autumn nights that seem safest are exactly when operators have the most to worry about

As fall colors Ontario’s trees, another seasonal change is taking place across the province’s wind farms. Bat fatalities are typically at their highest during late-summer activity periods and fall migrations.

Fatalities are particularly high on nights with low wind speeds, when bat activity remains elevated. Calm evenings and cooler weather also coincide with a challenging time for wildlife around wind facilities.

Wind energy remains an important source of renewable electricity. But questions remain about how turbines interact with birds and bats during migration periods.

Some locations create far greater risks for wildlife

Wind power projects can affect wildlife both directly and indirectly. Direct impacts include collisions with turbine blades and other structures. Indirect impacts include habitat disturbance and behavioral changes.

Monitoring done at Ontario wind facilities has indicated that mortality rates for birds tend to be less than bat fatality rates.

Mortality rates for birds due to wind turbines tend to be much lower than those associated with other human-related factors. These include window strikes, power-line collisions, and predation by household cats.

However, that doesn’t mean all locations carry the same amount of risk.

Ontario’s wind power guidance document states that proper siting is the number one consideration to minimize wildlife interaction.

Wind projects sited near migration routes, nesting sites, staging grounds, and large bird congregations can lead to increased risks. The same is true near roosts, breeding habitats, swarming areas, or hibernation sites.

Migration season leaves bats and birds more exposed

Different species react differently to wind power developments. Turkey vultures are among the bird species regularly killed at Ontario wind facilities.

These birds utilize soaring flight patterns, which make them less agile to avoid wind turbines.

They frequently travel long distances using thermals and winds, increasing the likelihood of encountering turbines.

While Turkey vulture mortality is high at some Ontario wind facilities, the number of bat mortalities is significantly higher. The Ministry of Natural Resources of Ontario estimates that more than one million bats are killed each year at wind power facilities throughout North America.

Most of these fatalities result from bat collisions with rotating turbine blades. In addition, researchers have documented that barotrauma also contributes to the total number of bat mortalities.

This internal damage results from the rapid changes in air pressure created by spinning turbine blades.

Many bat mortalities in Ontario involved long-distance migratory species such as hoary bats, eastern red bats, and silver-haired bats.

High-risk periods for bats usually coincide with mid-July through September, specifically during migration periods.

Prevention begins long before turbines start turning

The Wind Power Guidance Document indicates that wildlife interaction can be lessened before a project is built.

Turbine placement is the first layer of protection because it reduces the chances of birds and bats coming into contact with wind facilities.

If important habitat areas cannot be avoided, additional measures may need to be used to reduce those risks.

Some risks can only be reduced after construction

One example involves temporarily shutting down turbines during periods when the risk of wildlife mortality is known to be higher. Increasing turbine cut-in speeds has also proven effective at reducing bat fatalities.

Researchers are also investigating “smart” mitigation systems that only activate when bats are detected nearby.

Ontario requires monitoring before and during operation of wind power projects located near significant bird and bat habitat. In addition to bat mortality, bird mortality can trigger operational changes at specific turbines to reduce impacts on birds.

Wind turbines and wildlife do not exist independently of one another.

Each new wind facility increases the need for careful planning for species that migrate through multiple wind sites each year. The challenge is not simply generating electricity but generating it in ways that reduce risks to birds and bats.