Fragmentation and habitat conversion: Birds and other organisms evolved with native natural communities, whose habitat structure provides the variety of niche spaces that allow multiple species to co-exist. When those habitat types are converted to crop lands, non-native grass pastures, urban areas, energy development, etc., many species are unable to find the kinds of food, cover and nest sites that they need in the altered environments. The habitat conversion results in less acreage of suitable habitat being available to the birds and thus fewer pairs can be supported. In addition to the loss of habitat, remaining tracts often are smaller and more isolated than before the land conversion occurred, an outcome known as fragmentation. Fragmented landscape tend to support more predators and parasites of bird nests, causing a decrease in the number of offspring produced or adults who survive to breed again.
Fire suppression: Nearly all of the natural communities in the Central Hardwoods Bird Conservation Region evolved with periodic fire, set by Native Americans or sparked by lightning strikes. Fire acts as a thinning agent, leaving trees more widely spaced, or in the case of prairies and barrens, relegating them to areas where moisture accumulates like shallow wetlands and creek beds. The open canopy that results in woodland settings, in turn, allows more light to reach the ground and stimulate the growth of grasses and forbs. Fire suppression, which became popular in the mid-20th century, has allowed an unnaturally dense growth of trees to occur on woodland sites and effectively shaded out the native grasses and forbs associated with a diverse understory. The bird species that have suffered the greatest declines across the Central Hardwoods in recent decades are those associated with grassland and open-woodland systems.
Collisions: In the modern world, there are an ever-increasing number of barriers to bird flight, such as buildings, communication towers, windmills, etc. that cause direct mortality to millions of birds each year from collisions with those structures. While it’s unrealistic to expect that we’ll stop building, there are ways to make all of those structures less deadly though proper siting, lighting, use of proper building materials, and other means. CHJV partner, American Bird Conservancy, has several programs devoted to finding ways to reduce the mortality to birds from collisions. More information can be found at: www.abcbirds.org.