In autumn, concentrated groups of woodcock may not reflect the carrying capacity of land on which they're found, as they may just be passing through. The overall population can fluctuate greatly over the years. Steady human encroachment on wet woodland, timber maturation and flooding may pose threats to the woodcock population. Woodcock may be exposed to pesticides used to control either forest or agricultural pests. Contamination from agricultural pesticides is highest in wintering areas where woodcock feed in farm fields.
Earthworms are resistant to many chemicals, so they can carry toxins.
Since woodcocks are predators of earthworms, there's a chance they'll accumulate persistent toxic chemicals found in worms. That compares to a two percent average annual decrease over the same period throughout its North American range. Most biologists attribute this decline to loss of habitat quantity and quality. Development also destroys or fragments existing woodcock habitat. Habitat Habitat requirements for woodcock change throughout the year.