Editor’s note: According to a new study reported in the journal Science, bird populations in North America have experienced a troubling decline in the past five decades. The scientists estimate the continent has lost close to 3 billion birds, roughly 29% of their total numbers in 1970. Senior wildlife ecologist Thomas J. Benson of the Illinois Natural History Survey discusses the status of birds in Illinois with News Bureau life sciences editor Diana Yates. Benson leads the Critical Trends Assessment Program, which monitors the biological condition of the state’s forests, wetlands and grasslands, and collects data on plants, birds and arthropods.
What was your reaction to the new report in Science? Were you surprised?
I was glad to see this well-executed study examining continental declines over nearly five decades using two independent datasets. Sadly, I was not surprised by the results. Past studies have documented declines of some groups, but this is the most comprehensive examination to date. What may be surprising, even to those of us who conduct research on the topic, is the extent to which common birds have declined. Even habitat generalists, those able to breed in a wide variety of circumstances including urban, suburban and agricultural areas, have declined substantially.
Are bird populations declining this much in Illinois?
In many cases, declines in Illinois are even more extreme than continental averages. We’ve lost more than 80% of individuals for many grassland-dependent bird species over the past 50 years, and more than 80% of redheaded woodpeckers and whippoorwills, just to name a few. Even common species like blue jays and common grackles have declined by more than 60% in Illinois. We’re generally not fond of nonnative species like house sparrows and European starlings because they can be pests, but substantial declines in these invasive and otherwise very successful species (80% and 35% losses, respectively) indicate that we should be paying attention to larger factors that may be causing these declines.
What are the most important factors affecting bird populations in Illinois?
The biggest factor influencing bird populations in Illinois is land use. Conversion of native prairies, wetlands, savannas and forests to agriculture, towns and cities greatly altered bird populations in the state. However, agricultural intensification in the 20th and 21st centuries further affected birds. The shift from diverse agricultural landscapes characterized by small farms with multiple types of crops and livestock to contemporary landscapes dominated by large corn and soybean fields has negatively affected many species. Corn and soybean fields do not provide suitable habitat for many birds, and enlarging fields leads to decreases in fencerows or field borders that can be suitable habitat. Further compounding these changes, technological advancements in pest management, particularly chemicals, have had many negative direct and indirect effects on birds. Decreasing bird populations, of course, is not the intention, but declines are an unfortunate consequence of these changes.
The report found that grassland birds were experiencing the worst losses. Is this also true in Illinois, “the Prairie State”?
As with the trends for all of North America, losses of grassland birds in Illinois have been more extreme than for other groups. Most native prairie in Illinois had been converted to agricultural uses by 1900, and even agricultural grasslands that were once common have largely been replaced by row crops. Consequently, formerly common species that nest in grasslands, such as eastern meadowlarks, bobolinks, grasshopper sparrows, northern bobwhites and even introduced game species such as ring-necked pheasants, have all decreased by more than 80% over the past 50 years.
Are any types of birds doing well in Illinois?
Some species have responded well to the changes we’ve made to the Illinois landscape or to conservation measures enacted in recent decades. As seen in the continental analysis, wetland-dependent species, raptors and some other species are doing better in Illinois. The economic importance of waterfowl led to wetland conservation and restoration, actions that benefit waterfowl and other wetland species. The banning of DDT has benefited many species, including raptors. Some species benefit from human-altered conditions. Examples of species that fall into these groups and have increased in Illinois include great blue heron, wild turkey, American robin, chipping sparrow, red-tailed hawk, Cooper’s hawk and, of course, Canada goose, all of which have more than doubled.
Which birds are most at risk across the state?
Grassland birds continue to be at risk because of habitat loss, as do shrub-dependent birds such as those that were historically dependent on habitats like woody fencerows (northern bobwhite, field sparrow and brown thrasher, for example).
Can individual actions make a difference?
Individuals can take many actions to benefit bird populations. Most birds are migratory, so it's important to note that actions are needed in breeding, migration and wintering areas. Given that grassland- or shrub-dependent birds are most strongly affected by habitat loss, the biggest benefit for these species in recent decades has been Farm Bill programs such as the Conservation Reserve Program. Enrollment of lands in these programs, even field or stream borders, benefit at-risk species, and stressing the importance of these programs to lawmakers can make a positive difference. Two of the largest sources of human-related direct mortality for birds are predation by cats and window collisions during migration. Keeping cats indoors and exploring window treatments that reduce bird collisions are two ways to make a positive impact. Lastly, supporting scientific inquiry into the causes of, and remedies for, bird declines can help us seek solutions that mutually benefit birds and people.