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 have gotten many emails that indicate I failed to get across the point I wished to make. The columns were timed to lead up to Earth Week. But we should not try to tread lightly on our planet for only a week a year so I will provide this overview column.
Let’s consider loggerhead turtles as an apt analogy for the importance of understanding the impact of different sources of death for a species. Loggerhead turtles are an endangered species. Some are killed illegally for food, others are trapped in trawl nets by commercial fishing boats, and predators get some hatchlings are they stumble down the beach after hatching for their first swim in the ocean. 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.
However, modeling the population dynamics of loggerhead turtles revealed some intriguing truths. First, even if every egg were to hatch and every hatchling could make it to the water, the loggerhead turtle would still 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 of these turtles died from becoming entangled in trawl nets; the turtles drown when trapped in a net.
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 their nets. When a turtle is captured in a net, the TED opens up 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 different 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 that we should be trying to reduce these hazards first because of the sheer magnitude of the effects. As an unabashed cat lover, I know that keeping cats as indoor pets is the way to go for the safety of many birds and the safety of the cats. Proper placement of bird feeders and improving the visibility of glass in our houses can reduce collision-related bird deaths.
Do I therefore disregard deaths from wind turbine collisions? Of course not. As indicated earlier, I am a long-time 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. However, we need to realize that wind turbines pose threats to some species like cranes and eagles that are not likely to die from a cat attack (!) or a window collision.
We all need to take energy conservation more seriously. Better yet, we should be practicing energy avoidance. We can thereby 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.
[Originally published on May 11, 2014]