Why Not Let Nature Take Its Course?

So often, we hear "why not let nature takes its course" when dealing with the public regarding wildlife rehabilitation. Here are some eye-opening estimates of "un-natural" mortality.

Death By Cat

Cats, both feral and domestic, are among the biggest contributors to wildlife mortality. Cat predation accounts for the deaths of hundreds of millions of birds and more than a billion small mammals each year. One cat was responsible for the complete erradication (in a matter of months) of one whole species of bird on an island in New Zealand. Wildlife are particularly vunerable to cats in the spring when they are distracted while caring for their young. Cats are not part of the natural ecosystem. They do not hunt for survival, merely for sport. For the wildlife that are able to escape an attack, many will still die from the bacterial infection passed to them from the cat. One survey showed that 75% of wildlife admitted to animal welfare agencies, zoos, and rehabilitation groups for treatment had cat-related injuries. There are an estimated 80 million cats in the United States, with only approximately 35% of the cats kept indoors. A combination of studies estimates that 65-80% of cats routinely kill between 4-22 wildlife birds, small mammals and native reptiles and amphibians each per year.


Bird Mortality

Window Strikes = 97 to 976 million deaths annually
Communication Towers = 4 to 50 million deaths annually (A single-night kill of between 5,000- 10,000 Lapland Longspurs and other songbird species was recorded at 3 towers in western Kansas in 1998.)
Power lines = Up to 174 million deaths annually
Electrocutions = 10's of thousands of deaths annually
Vehicle collisions = 60 million deaths annually
Wind turbine rotors = 33,000 deaths annually
Pesticides = 72 million deaths annually (this figure does not included orphaned chicks or secondary poisoning)
Oil pits = 2 million deaths annually
Cats = hundreds of millions of deaths annually (In Wisconsin alone, rural cats are estimated to kill between 8 million and 219 million birds annually; this figure does not include feral cats, and domestic cats in suburban or urban areas)
Fishery by-catch = tens to hundreds of thousands of seabird deaths annually
Harvested = 17,301,700 geese, ducks, coots in 2002

Road Mortality

No estimated figures are available for mortality along roads and highways, but it goes without saying that the numbers would be staggering. During a 14-month period along a dual lane highway, road mortalities were documented for 11 species of mammals, 12 species of birds, 5 species of reptiles, 9 species of amphibians, and insects belonging to 11 orders (and more than 249 different species) (Seibert and Conover 1991). Road-related mortality was a significant threat to raptors, especially northern saw-whet owls and eastern screech owls (Loos and Kerlinger 1993), but road kill numbers varied with season, location, road type, and species involved. A study of screech owl deaths in Pennsylvania determined 72% to be vehicle-collision related. Casualties of waterfowl, doves, robins and squirrels are common on suburban roads.

Human Disturbance

Quite often, normal human surroundings and routine activities negatively impact wildlife. Tree pruning and tree removal destroys the nests of birds and squirrels. Birds and mammals are suseptible to poisoning from ordinary lawn herbicides, grubicides, and lawn pesticides (Diazinon, Sevin, Malithion), either from ingestion or direct contact. Sticky fly paper, rodent traps and glue traps can catch almost every species of small bird (including hummingbirds) and small mammals. Monofilament fishing lines becoming entangled around the legs and feet of ducks and gulls. The intentional trapping and relocation of resident wildlife results in death when the animal is placed in an unfamiliar location with no shelter or established food source. There have been reported cases of opposums, raccoons and foxes with their heads trapped inside plastic food jars. They die either from suffocation and/or a combination of dehydration and starvation. Ducklings can become trapped inside storm drains. Children playing near nesting sites may discourage feedings, resulting in hungry babies venturing out and becoming discovered.