The presence of humans without dogs caused significant declines in diversity and abundance of birds, but the impacts of dogs, even restrained on-leash, resulted in greater displacement of birds and more severely diminished local bird fauna. Considering a zone within 50 meters (about 150 feet) of the trail as the zone of influence by dogs (all on-leash), observations indicated that “dog walking in woodland leads to a 35% reduction in bird diversity and 41% reduction in abundance. These results argue against access by dog walkers to sensitive conservation areas.” “Local wildlife does not become habituated to continued disturbance by dogs.”

Three treatments, consisting of solitary pedestrians, a pedestrian accompanied by a dog on-leash, and a dog alone (all treatments both on- and off-trail), were used to study effects on mule deer and three songbird species. Wildlife responses varied near trails. All four species were negatively affected by off-trail users.

At four lowland riparian sites in eastern Boulder County, clay eggs were used to simulate bird nests to study predation rates at varying proximity to recreational trails. Birds attacked more nests near trails than away from trails, but native predatory mammals (e.g., mice and squirrels) appeared to avoid nests near trails to some extent. “These results support the contention that recreational trails and human activity may affect nesting success for some species.”

Written by an employee of the Idaho Fish and Game Department, this short article describes harassment and predation by dogs that resulted in direct and indirect mortality of deer in northern Idaho where residences are interspersed throughout deer winter range.

Sarah E. Reed & Adina M. Merenlender, Quiet, Nonconsumptive Recreation Reduces Protected Area Effectiveness

Protected areas around the world were created with the goals of preserving biodiversity and providing nature-based recreation opportunities for millions of people. This dual mandate guides the management of the majority of the world’s protected areas, but there is growing evidence that quiet, nonconsumptive recreation may not be compatible with biodiversity protection. We combined noninvasive survey techniques and DNA verification of species identifications to survey for mammalian carnivores in 28 parks and preserves in northern California. Paired comparisons of neighboring protected areas with and without recreation revealed that the presence of dispersed, nonmotorized recreation led to a five-fold decline in the density of native carnivores and a substantial shift in community composition from native to nonnative species. Demand for recreation and nature-based tourism is forecasted to grow dramatically around the world, and our findings suggest a pressing need for new approaches to the designation and management of protected areas.

Bird species diversity, composition, and abundance were assessed in proximity to recreational trails on City of Boulder open space in 1994-95. In both grassland and forest ecosystems, areas with increasing distance from trails harbored more species, more individuals, and higher nest survival of young birds, for many important bird species. A nest predator (magpie) fared better closer to trails.

Transient human activity disturbs birds, leading to declines in species numbers.

A close association was found among recreational path density, high levels of fragmentation, weed infestation, and low vegetation condition.

Horses turn up more soil than hikers leading to more sediment yield and thus creating more erosion.

Horses, more than hikers, expose soil and have greater impact on relative cover of resident vegetation. The study area included two types of forest vegetation.

Because it is common for horses to graze in “weedy” pastures and because their feed may be contaminated by alien plants, horses may be an important cause of introducing invasive plant species far into previously non-invaded wildlands. In this study, seedlings were grown from samples of horse dung collected along a recreational trail in the White River National Forest (Colorado). In replicate plantings, 85% of seedlings were alien species. “Our results make clear that horses used on recreational trails represent a potentially important dispersal vector for alien plants in western wildlands.”

A Wildlife Biologist for the Montana Fish, Wildlife, and Parks (Kalispell) writes, “domestic dogs do pick up and transport seeds in their hair and paws. While the scale of noxious weed seed transport by dogs is small compared to that of motorized vehicles, dogs can travel and deposit seeds in locations far removed from roads and trail systems. Because these areas are not traveled as frequently as roads, emerging weed plants may go undetected and not be treated in a timely manner.”

Frequent soil disturbance causes more cheatgrass in invaded areas, and higher seed availability causes faster invasion. Disturbance and cheatgrass invasion are connected primarily by the ways in which disturbed soils acquire and utilize water.

There is a strong connection between disturbance of grassland and shrubland and the invasion of cheatgrass.

The effects of soil disturbance of mixed grass prairie by prairie dogs, roads, and constructed trails were studied in national parks in North and South Dakota. Exotic species were more likely than native weeds to have spread beyond the disturbed areas into native prairie.

From 74 cited scientific articles, the authors categorized original reports of impacts, including 91 reports on impacts related to hiking/camping and wildlife observation/photography. Of these, 65 reports documented negative effects (16 concluded indeterminate or no effect).

For decision-makers, this document articulates the scientific principles that may inform policies to implement the Visitor Master Plan, summarizes consequences of alternative actions regarding these policies, and states the relevance of the precautionary principle.

• Overview, Chapter 1
• Amphibians and reptiles, Chapter 2
• Birds, Chapter 3
• Small mammals, Chapter 4
• Semi-aquatic mammals, Chapter 5
• Ungulates, Chapter 6
• Carnivores, Chapter 7
• Domestic dogs in wildlife habitats Chapter 8
• Vegetation, soils, and water, Chapter 9
• Online bibliography, Chapter 10

This study compared prairie sites with a riparian corridor, with and without pedestrian/biker trails in the riparian corridor. In sites with no trails, species richness, perching frequency, and abundance of raptors was greater. Eagle abundance was strongly affected by the presence of trails.

Population density of Preble’s Meadow Jumping Mouse was 31% lower on sites with trails than on sites without trails.

The compilation is organized into the following sections:

1. Effects of dogs on wildlife
2. Effects of recreational trails on habitats/wildlife
3. Effects of horses on soil stability and erosion
4. Effects of horses on spread of weeds
5. Effects of dogs on spread of weeds
6. Effects of other or general disturbances on the spread of non-native species
7. Review articles and other resources