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Planning Trails with Wildlife in Mind

The construction of a trail is just one impact on the habitat it passes through. The activities of visitors and the response of wildlife are also components of the long-term trail impacts.

 

H. How wildlife respond to trails

Wildlife and Trails Primer - Key Concepts and Rules of Thumb

 

Once a trail is built, its physical presence also can change its environs. The trail may have created a new ecological edge, perhaps increasing the light intensity and prompting a shift in the composition of wildlife and plant species, thus changing biological diversity.


KEY CONCEPTS

photo of trail with elk watching

Seeing wildlife adds to the richness of our experience, but
understanding how wildlife respond to humans is important as well

Impacts of a trail will depend on the type of trail use (e.g., hiking, snowmobiling, biking). These uses do not represent a continuum with hikers at the low-impact end and motorized recreationists at the high end; wildlife impacts are more complicated than that.

That is why, for example, some wildlife refuges allow auto tours but not walking tours because many wildlife species are less fearful of people in vehicles.

Sometimes the response of wildlife to a trail doesn’t last long, as when a bird stops feeding as a hiker approaches, only to continue eating after the hiker has passed. With increasing levels of use and changes in the type of use, there may be sufficient disturbance along a trail that some wildlife may move away permanently.

Predictability can be a major factor in how much disturbance a trail user causes. If trail users stay on a trail they are more likely to be perceived as acting in a predictable fashion and therefore as less of a threat.

Dogs can cause considerable disturbance (because they may chase and kill wildlife), but less so if they are on a leash and don’t leave the trail.

Paradoxically, bird watching and other forms of nature viewing that intentionally seek out close encounters with wildlife may have a significant impact.

Factors affecting the short-term impact of human disturbance on wildlife include:

• Type of species and flushing distances;
• Type and intensity of human activity
• Time of year and time of day; and
• Type of wildlife activity (feeding, nesting, roosting, migrating).

For example, a slowly moving birdwatcher may impact the birds he approaches, but only over a more localized area than a speeding motorcycle that may have a briefer impact on any one area, but impact a broader area. If an animal responds to a noise as soon as it hears it, noisy vehicles may affect it at a greater distance than humans can typically be heard.

Wildlife characteristics, including type of animal, group size, age, and sex, also determine the response to a disturbance.
Disturbance by humans can cause nest abandonment, decline in parental care, shortened feeding times, increased stress, and possibly lower reproductive success.

Trails often pass through areas used by hunters. Hunting, by design, affects wildlife. In general, even though hunting reduces animal populations annually, it is often of short duration, closely controlled, and can be used as a wildlife management tool.

In weighing impacts to wildlife, attention is often given to effects on biological diversity. Biodiversity is not equivalent to species diversity. It is more than just a count of how many species use an area. “Biodiversity is the variety of life and its processes. It includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever changing and adapting” (Noss and Copperrider).

Although the presence of large numbers of exotic species may boost the count of species in an area, it would probably indicate declining biodiversity due to loss of native species. Exotic species frequently out-compete natives and replace them.

 

RULES OF THUMB

H.1 Lack of wildlife knowledge.
Because there isn’t much detailed knowledge about the effects of human disturbance on wildlife, be cautious in planning a trail, carefully weighing the alternatives.

H.2 Make do.
Use the best wildlife information available, even if it is scarce. Get the advice of a biologist.

H.3 Considerable differences. Not only do different species respond differently to trails, different popula- tions of the same species may respond differently, based on previous encounters with people.

H.4 Concentrated use.
Generally, it is better to concentrate recreational use rather than disperse it. If social trails have developed in an area, it is probably better to consolidate them into one or a few trails.

H.5 Type of trail use.
Some wildlife are more alarmed by hikers than by people who stay in their vehicles, especially if the vehicles don’t stop.

H.6 Dog controls.
If dogs are to be allowed on a trail where there are sensitive wildlife, the dogs should be leashed or excluded seasonally to reduce conflicts.

H.7 Screening.
The natural visual screening of a trail in a wooded area frequently makes most wildlife tolerate greater human disturbance than they would in open terrain. In some areas, it may be possible to plant a vegetative screen or build a screening fence to accomplish similar effects.

H.8 Impacts vs. benefits.
Don’t assume all wildlife impacts can be resolved through management. There may be situations where the negative impacts of a trail to wildlife outweigh the benefits to trail users and a trail should take a different alignment.

H.9 Breeding areas.
Either avoid wildlife breeding areas or close trails through them at the times such wildlife are most sensitive to human disturbance.

H.10 Enforcing closures.

If there won’t be sufficient resources to enforce a trail closure during wildlife-sensitive seasons, consider rerouting the trail through another area.

 

arrow down Flight Distances for a variety of wildlife. Studies have documented a range of responses by wildlife to various forms of disturbance. (This chart was developed from a review of the published literature by Clinton Miller, City of Boulder Open Space, 1994). While these numbers don’t specify how far a trail needs to be from wildlife to avoid disturbance, taken together they illustrate a variability based on the species of wildlife and types of disturbance.

Species

Disturbance Factor

Flight Distance*

Mule deer Person on foot —In low disturbance area 330 m
  — In medium disturbance 250 m
  — In high disturbance 200 m
  — recommended to avoid most flight 191 m
Mule deer person afoot in winter 200 m
Elk person afoot in winter 200 m
  highway vehicles 77 m
Elk cross country skiers in —high use area 15 m
  — low use area 400 m
Mountain sheep person afoot in winter 50 m
Golden plovers people on trail 200 m
Eider ducks
land-based disturbance —with a dog 103 m
  — without a dog 52 m
American Kestrel
disturbance of person afoot winter 75 m
Merlin disturbance of person afoot winter 125 m
Prairie Falcon
disturbance of person afoot winter 160 m
Rough-legged hawk disturbance of person afoot winter 210 m
Ferruginous Hawk
disturbance of person afoot winter 140 m
Golden Eagle disturbance of person afoot winter 300 m
Bald Eagle
land activities near roost on shoreline 250 m
Great Blue Heron land-based activities 200 m
  — water-based activities 100 m

*Note: Flight distance is the measurement from the source of the disturbance to the animal when the animal physically flees to a safer location, not the distance at which the animal first responds or is aware of the disturbance.

 

Further Reading

[Older publications may be available from libraries and used booksellers. Titles with links may still be in print.]

Knight and Cole, “Wildlife Responses to Recreationists,” in Knight, R. and K. Gutzwiller, eds., 1995. Wildlife and Recreationists: Coexistence through Management and Research. Island Press, Washington, D.C., pp. 51-69.

Knight and Cole, “Factors that influence Wildlife Responses to Recreationists,” in Knight, R. and K. Gutzwiller, eds., 1995. Wildlife and Recreationists: Coexistence through Management and Research. Island Press, Washington, D.C., pp. 71-79.

Noss, R. and A. Cooperrider, 1994. Saving Nature’s Legacy: Protecting and Restoring Biodiversity. Island Press, Washington, D.C.

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