Living in a world full of hazards
July 8, 2015
VCU Rice Rivers Center collaborator: Center for Conservation Biology
By Bryan Watts
Black over red 3-8 was a male peregrine falcon that was hatched on a railroad bridge that crosses the Elizabeth River in Norfolk, VA, in 1993. Within 3 years the bird established a new breeding territory on the Benjamin Harrison Bridge near Hopewell, VA, and produced 27 young over the next 10 years. On 12 February 2007 the bird was found dead near the bridge. Like so many other peregrines that we have tracked over time, the old male flew into a guy wire and was killed.
We kill billions of birds across the globe every year. Many of these birds are like 3-8, unintentional casualties of the infrastructure we have built to support modern society. They fly into hazards that we have erected in their airspace like tall buildings, transmission lines, radio towers, and wind turbines. They are poisoned by chemicals or soiled by oil spills. They become entangled in fishing gear or are hit by cars or trains or airplanes. Some are killed intentionally by hunters or by people who classify them as pests.
Like with human mortality, we have spent considerable time and effort to quantify the major causes of death. In the United States alone, we estimate that every year nearly 60 million birds are killed by vehicles, 50 million are killed by communication towers, 70 million are killed by pesticides and possibly as many as 1 billion are killed when they fly into buildings. A recent study has estimated that free-ranging domestic cats in the United States kill more than 1 billion birds annually. Understanding mortality factors is an important step toward improving survival. However, mortality factors represent only one side of the story.
From a conservation perspective, the central question is not how many individuals are killed annually but whether populations have the capacity to absorb the mortality incurred and still reach management objectives. Understanding the relationship between realized mortality rates and sustainable mortality limits serves to focus management actions on factors that have the potential to cause population declines. Over the past several years, The Center for Conservation Biology has been borrowing from harvest theory to estimate sustainable mortality limits for species of conservation concern.
In 2010, CCB evaluated sustainable mortality limits for waterbird populations using the Western North Atlantic to provide a foundation for understanding potential impacts of offshore wind development (read Wind and Waterbirds). More recently, we have worked with the Canadian Wildlife Service and the U.S. Fish and Wildlife Service to estimate sustainable mortality limits for populations of migratory shorebirds using the Atlantic Flyway to better understand the potential impact of shorebird hunting. A paper from this work will be published during the summer of 2015 and is now available online. Following this effort, we have recently worked to estimate sustainable mortality limits for shorebirds using the East Asian-Australasian Flyway to better understand how hunting and other factors may be causing population declines.