USDA Forest Service Res. Note RMRS-RN-3. 1998 1

United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Research Note

RMRS-RN-3

September 1998

Abstract: We measured noise levels of four logging trucks

as the trucks passed within approximately 500 m of two

active northern goshawk (Accipiter gentilis) nests on the

Kaibab Plateau in northern Arizona in 1997. Neither a

brooding adult female nor a lone juvenile exhibited any

discernable behavioral response to logging truck noise, which

peaked at 53.4 and 50.3 decibels (dBA). Spectral analysis

showed most of the truck sound energy was in the vicinity

of 80 Hz.

Keywords: northern goshawk, Accipiter gentilis, truck noise,

sound measurement, disturbance

Management of potentially disturbing human

activities in the vicinity of nesting northern goshawks

(Accipiter gentilis) is an important issue in the Southwest (Reynolds et al. 1992); however, data on the

possible effects of associated noise alone are lacking. To

establish initial baseline distances and noise levels

for evaluating responses of nesting goshawks, we

were able to take advantage of a salvage logging operation on the Kaibab Plateau in northern Arizona,

Coconino County, during the summer of 1997. As part

of the logging process, loaded trucks used secondary

graveled roads close to several nesting goshawks.

Based on logging schedules and nesting activity, we

chose two active nest sites in ponderosa pine (Pinus

ponderosa) forest at approximately 2130 m elevation

as locations to record noise levels and associated

goshawk responses.

Logging Truck Noise Near

Nesting Northern Goshawks

Teryl G. Grubb

Larry L. Pater

David K. Delaney

Methods _______________________

Noise data were obtained by means of a Bruel &

Kjaer (B&K) professional microphone system consisting of a type 2804 power supply, type 2639 preamplifier, type 4149 1.3-cm microphone, and 7.5-cm foam

windscreen. The system was calibrated by means of a

1-kHz 94 dB signal from a B&K type 4250 calibrator.

All data and calibration signals were recorded on a

Sony TCD-D7 digital audio tape (DAT) recorder for

detailed laboratory analysis. Data analysis was performed with a B&K type 2144 frequency analyzer. We

described noise measurements by using maximum

one half-second equivalent average sound level (LEQ),

referenced to 20 micro-Pascals and A-weighted (dBA,

human-based weighting algorithm ubiquitously used

and included on most noise meters). Goshawk behavior

was monitored from blinds 15-25 m from nest trees.

Our opportunistic pilot test involved recording noise

levels of four logging trucks passing within 413 m of

an adult female brooding week-old young on 10 June,

and two trucks passing within 513 m of another nest

containing a lone, 7-week-old juvenile on 27 July.

Microphone placement beneath the nest trees was

within 3-4 vertical m of the road level at its closest

point.

Results ________________________

Neither the brooding adult female nor the lone

juvenile exhibited any discernable behavioral response

to logging truck noise at the distances and levels

measured. Only two of the six truck passes (53.4 and

50.3 dBA) were louder than ambient noise levels

(34.1 dBA); both occurred at the brooding female site.

These trucks were audible for 2-3 min, with sound

levels increasing to maximum decibel levels when

truck-to-nest distance was the least then rapidly decreasing as truck-to-nest distance increased. The

other trucks were barely discernable to the human

Teryl G. Grubb is Research Wildlife Biologist, Rocky Mountain

Research Station, 2500 S. Pine Knoll Dr., Flagstaff, AZ 86001.

Headquarters is in Fort Collins, CO. Larry L. Pater is Acoustical

Engineer and David K. Delaney is Research Wildlife Biologist, U.S.

Army Construction Engineering Research Laboratories, P.O. Box

9005, Champaign, IL 61826.

Use of trade names does not imply endorsement by the USDA

Forest Service or U.S. Army C.E.R.L. to the exclusion of other

potentially suitable products.
2 USDA Forest Service Res. Note RMRS-RN-3. 1998

ear and were easily masked by high altitude jet

aircraft passing over, or even light breezes (<16 km/hr)

rustling through the canopy. Both nesting pairs were

successful in fledging their young.

Spectral analysis of the truck noise showed that most

of the sound energy was located in the vicinity of 80

Hz, which is consistent with exhaust noise of large

diesel trucks under load. Sound level in the 1/3-octave

band centered at 80 Hz was at least 20 dB higher

than the sound level in other bands (except for some

very low frequency noise due to wind over the microphone) and at least 20 dB higher than ambient noise.

Because decibels are measured on a logarithmic scale,

every 6 dB difference between ambient and event

noise represents a doubling of sound level.

Discussion _____________________

There is little published information regarding

the hearing range and sensitivity for birds of prey.

Trainer (1946 as cited in Fay 1988) found the American

kestral (Falco sparverius) exhibited a typical avian

audiogram (graphic relationship between hearing

range and sensitivity), albeit somewhat more sensitive in the mid-frequencies. In general, birds hear well

in the range from 100 Hz to 8-10 kHz but have a

narrower hearing sensitivity range than most mammals including humans, i.e., birds’ hearing is less

sensitive at both high and low frequencies. Logging

truck noise, at 80 Hz, is quite low in frequency and

therefore may be less noticeable to birds, or in this

case goshawks, than to human observers.

Wind, topography, forest vegetation, and truck and

road characteristics can all affect ultimate noise

levels at the target species. In our experiment, vegetation, topography, wind, and truck and road characteristics were similar between the two test sites.

However, these factors should be addressed in any

future studies. Our initial testing indicates that logging trucks passing >400 m away from nest sites in

forested habitat result in noise levels <54 dBA, and

that such levels are not disturbing to nesting northern goshawks.

Acknowledgments ______________

We thank D. Garcia, D. Sinton, and M. Howard of

the North Kaibab Ranger District, Kaibab National

Forest for making this research opportunity possible

and facilitating field data collection. K. Menasco and

M. Siders critically reviewed the original manuscript.

Literature Cited _________________

Dooling, R.J. 1982. Behavior and psychophysics of hearing in birds.

Pages 261-288 in Popper and Fay, eds., Comparative studies of

hearing in vertebrates. Springer-Verlag, New York, NY.

Fay, R.R. 1988. Hearing in vertebrates: a psychophysics handbook,

Hill-Fay Assoc., Winnetka, IL.

Reynolds, R.T., R.T. Graham, M.H. Reiser, R.L. Bassett, P.L. Kennedy,

D.A. Boyce, Jr., G. Goodwin, R. Smith, and E.L. Fisher. 1992.

Management recommendations for the northern goshawk in the

southwestern United States. USDA Forest Service Gen. Tech.

Rep. RM-217, Ft. Collins, CO.

Trainer, J.E. 1946. The auditory acuity of certain birds. Ph.D. thesis.

Cornell Univ., Ithaca, NY.