Larry L. Pater (217-373-7253, L-PATER@CECER.ARMY.MIL)
U.S. Army Construction Engineering Research Laboratories
Champaign, IL
David K. Delaney and Teryl G. Grubb
Rocky Mountain Forest and Range Experiment Station
USDA Forest Service
Flagstaff, AZ.
M. Hildegard Reiser
Holloman Air Force Base, NM.
Paul Beier
School of Forestry
Northern Arizona University
Flagstaff, AZ.
Popular Version of Paper 4aAB5
Presented Thursday, November 30, 1995
Acoustical Society of America, St. Louis, Missouri
This research addresses noise impacts on the Mexican spotted owl (Strix occidentalis lucida) subspecies found in the Southwest. Stimuli will include low level helicopter flights and noisy ground activities such as chain saws and motorcycles. The product will be dose-response threshold models that quantify flight response probability relative to sound stimulus levels and approach distances. The project will help to develop disturbance-specific management guidelines to minimize potential audio/visual impacts from helicopter and ground activities.
Many Federal agency activities, including critical military training, cannot continue unless they comply with environmental regulations including the Endangered Species Act (ESA). The ESA requires Federal agencies to assess impacts of their activities on threatened and endangered species (TES) and to carry out programs for the conservation of listed species. This assessment is the basis for coordination with the U.S. Fish and Wildlife Service, which issues a biological opinion and specific endangered species management recommendations. In some cases activities, including military training, are curtailed because of potential impacts. In the absence of definitive data, a conservative course of action may be adopted. Such a course may protect the animal but be costly to the agency and the public.
This research project quantifies impact in terms of flight response of non-breeding owls, effects on nest attentiveness of breeding females, and the rate of prey delivery to the female by breeding males.
Other issues include habituation to the noise, probability of exposure, the bird's hearing range and sensitivity, and the sound level received at roost and nest sites. The noise stimuli will be presented to the birds at a variety of distances and in a realistic manner. The experiments must be conducted in the high altitude forests in which the birds are found. The detailed study plan gives careful attention to statistical significance of the data, exposure repetitions, and study and control groups.
Measurements have already been made under controlled conditions to establish noise level vs. distance from the source. Noise level measurements will be made during the experiments in a way that enables accurate evaluation of noise level at the birds' locations, and will also serve as a check on the distance of the helicopter from the bird during the brief flyover exposure. The research team has expertise in both biology and acoustics.
No published research addresses noise impacts on the spotted owl. Most of the information currently available regarding the effects of noise on TES is anecdotal, usually chance observations made under undocumented conditions. There is a profound lack of authoritative data and proven scientific models. Such information is needed to assess and manage the effects of existing and proposed activities for purposes of environmental protection and operational planning.
Human reaction to noise depends not only on noise level but also on the type of noise. It has also been found that different types of noise require different measurement quantities. Both the hearing range of the subject animals and the acoustic energy spectrum of the noise (the frequency, or "pitch," at which the noise energy occurs) need to be considered. For example, the ubiquitous "A-weighted" noise measurement de-emphasizes noise that occurs outside of the human hearing range. Standard noise metrics suitable for humans are not necessarily appropriate for any particular animal species. Existing mathematical models for noise sources and algorithms for noise propagation can be readily adapted to calculation of noise levels for animals as well as humans.
A important issue is the criteria for impact on a wildlife species. Ideally the impact on long term population status would be assessed. However, such a study might need to cover several generations. Expediency requires selection of indicators that can be definitively studied in a practical time and cost frame. Candidate indicators of impact include success of rearing offspring, behavior, physiological parameters, and energy acquisition (feeding) and expenditure. Modifications in behavior can be subtle. It is important to consider whether a change in behavior is detrimental or inconsequential.
Working with threatened or endangered species entails unique difficulties. Statistical significance is an issue, since the number of individuals that can be exposed to various treatments during the study may be small. An alternative is to use a surrogate species, i.e., use results from study of non-threatened animals to infer response of threatened animals. Relevancy and applicability of results can be thorny issues. Other difficulties include large numbers of variables that are difficult to control in the wild and the variability among individuals of many ecological and behavioral factors. And, of course, the study must be conducted in a manner that does not further endanger the survival of the species.