Response of nesting northern goshawks to logging truck noise in northern Arizona

Abstract

We recorded 94 sound-response events at 3 adult-occupied northern goshawk (Accipiter gentilis) nests 78 m, 143 m, and 167 m from the nearest United States Forest Service maintenance level 3, improved gravel road on the Kaibab Plateau in northern Arizona. During 4 test sessions on 7, 8, 10, and 11 June 2010, we recorded 60 experimentally controlled logging trucks; 30 non-experimental, civilian, fixed-winged aircraft; 3 non-experimental, passing cars; and 1 all-terrain vehicle (ATV). Logging truck sound, principally engine and exhaust, was concentrated in the 63 Hz and 80 Hz, 1/3-octave frequency bands. Aircraft sound was concentrated in the 100 Hz and 125 Hz, 1/3-octave frequency bands. Logging truck noise levels varied among nest sites and with distance from roads. At 167 m from the closest road, the logging truck averaged approximately 8 decibels (dB, all decibel levels C-weighted, adjusted, 1 s, equivalent sound level, CLEQ) quieter than aircraft. At 143 m, the logging truck was approximately 3 dB quieter than passing aircraft. Only at 78 m was logging truck noise louder on average than aircraft, by approximately 6 dB. Average aircraft noise levels for each day of testing ranged between 45.6 dB and 67.9 dB and when averaged across the entire study period, varied little among the 3 test sites, 60.1–65.6 dB. On average, our test logging truck (61.9 dB) was no louder than passing aircraft (62.3 dB), which goshawks generally ignored. The logging truck resulted in 27% no response and 73% alert (head turning) response, passing aircraft resulted in 90% no response and only 10% alert response, and the cars and ATV combined resulted in 50% each for no response and alert response. Goshawk alert response rates were inversely proportional to nest distance from the nearest road, decreasing from 91% to 57% alert between 78 m and 167 m. No movements or flushes were associated with either our experimental testing or passive recording of other vehicular noise stimuli. All tested pairs of goshawks successfully fledged young. Because logging truck noise had no effect on northern goshawks nesting along level 3, improved gravel roads on the Kaibab Plateau, restriction of log hauling and other road-based travel activities on similar roads within post-fledging family areas (PFAs) appears unnecessary based on the type and extent of our testing. © 2013 The Wildlife Society.