The last three columns were devoted to a consideration of the various human-related sources of bird deaths. Perhaps because some readers read only one or two of the columns, I received emails saying I failed to get across the point I wished to make. The columns were timed to lead up to Earth Week, but we shouldn’t try to tread lightly on our planet for only a week a year, so here’s an overview.

Let’s consider loggerhead turtles as an analogy for the importance of understanding the impact of sources of death for a species. Loggerhead turtles are endangered. Some are killed illegally for food, others are trapped in trawl nets by commercial fishing boats and predators get some hatchlings as they stumble down the beach for their first swim after hatching. Nests on sandy beaches are often lost to predators, including dogs.

For decades, conservationists have monitored the arrival of loggerhead females on nesting beaches. These people may cordon off the nest site to keep egg predators away. Hatching turtles may be accompanied by humans as the turtles head to the water for the first time. These efforts have saved many turtle lives.

But modeling the population dynamics of loggerhead turtles revealed intriguing truths. First, even if every egg were to hatch and every hatchling could make it to the water, the loggerhead turtle would go extinct under present conditions The model further showed that the critical stage of the life cycle is the 5-7 year-old turtles. Many died from becoming entangled in trawl nets; the turtles drown when trapped.

To reduce these deaths, the federal government is mandating that trawlers fishing in areas where loggerhead turtles occur must have turtle excluder devices (TEDs) installed on nets. When a turtle is captured in a net, the TED opens to allow the sea turtle to escape. The power of the model lies in showing environmental managers which stage of the life cycle should be targeted for conservation efforts. Protecting the 5-7 year-old juveniles is more effective than protecting eggs.

Reducing human impacts on bird deaths requires a similar approach. We need to understand the magnitude of the types of human-related mortality. The last column described by far the two most potent sources of bird deaths related to humans: building collisions and cats. My argument is we should be trying to reduce these hazards first because of the magnitude. As a cat lover, I know keeping cats as indoor pets is the way to go for the safety of many birds and the safety of the cats. Placement of bird feeders and improving the visibility of glass in our houses can reduce collision-related bird deaths.

Do I disregard deaths from wind turbine collisions? Of course not. I am a longtime opponent of mountain-based wind farms. Any bird death from human causes should be of concern. Collectively, wind farms result in far fewer deaths than cats or building collisions. But we need to realize wind turbines pose threats to species like cranes and eagles that aren’t likely to die from a cat attack or a window collision.

We all need to take energy conservation more seriously. Better yet, we should practice energy avoidance. We can reduce the need for more coal-burning power plants pumping carbon dioxide into the atmosphere as well as wind farms and hydroelectric dams that cause the loss of habitat.

Birding locally reduces bird deaths from car collisions and cuts down on carbon dioxide emissions. Buy a carbon dioxide offset to mitigate the carbon dioxide released from your car or plane travel.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at [email protected]