Impacts of Anthropogenic Noise on Wildlife: Research Priorities for the Development of Standards and Mitigation

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Notes

For a review of noise impacts on birds and other wildlife, see P. A. Kaseloo & K. O. Tyson, Synthesis of Noise Effects on Wildlife Populations (U.S. Department of Transportation, Federal Highway Administration, 2004); Robert J. Dooling & Arthur N. Popper, The Effects of Highway Noise on Birds (California Department of Transportation, Division of Environmental Analysis, 2007).

The geographic bias in research has lead to a focus on species that live in temperate zones, with little to no study of tropical species. Also of concern, many of the landscapes that have been the focus of research on noise and wildlife in these industrialized nations have already been profoundly influenced by human development such that the species or individuals living in these areas may be more tolerant of disturbance. Application of the results of studies from developed to less developed landscapes would potentially lead to an underestimation of the effects of noise. Anthropogenic changes to the environment are occurring at an unprecedented rate in developing nations in tropical latitudes, however, we do not yet know whether the results from existing research are applicable in these regions.

Many terrestrial noise sources produce noise that travels through the ground as well as the air. Seismic noise is likely to impact fossorial animals and animals that possess specialized receptors for seismic detection, many of which communicate by seismic signals. We do not address seismic noise in this paper, but it is an issue that warrants further discussion.

For recent treatments of noise in the marine environment, its impacts on marine species, and legal and policy responses, see Noise Pollution and the Oceans: Legal and Policy Responses Part 1, 10 J. Int’l Wildlife L. & Pol’y (2007) 101–199 and Noise Pollution and the Oceans: Legal and Policy Responses Part 2, 10 J. Int’l Wildlife L. & Pol’y (2007) 219–288. See also, Committee on Characterizing Biologically Significant Marine Mammal Behavior, Marine Mammal Populations and Ocean Noise, Determining When Noise Causes Biologically Significant Effects 142 (Ocean Studies Board, Division on Earth and Life Studies, National Research Council, The National Academies, 2005).

Birds have often been used in noise research because birds are generally easy to study due to their high detectability, most species use vocal communication (making them likely to be impacted by noise) and they are generally of high conservation importance.

R.T.T. Forman & R.D. Deblinger, The Ecological Road-Effect Zone of a Massachusetts (U.S.A.) Suburban Highway, 14 Cons. Biol. 36–46 (2000); R.T.T. Forman, Estimate of the Area Affected Ecologically by the Road System in the United States, 14 Cons. Biol. 31–35 (2000); R.T.T. Forman, B. Reineking, and A.M. Hersberger, Road Traffic and Nearby Grassland Bird Patterns in a Suburbanizing Landscape, 29 Envt’l. Mgmt. 782–800 (2002). Due to its ubiquity, road noise is the most commonly studied type of terrestrial noise. Road noise is, in general, similar to other types of anthropogenic noise and affects a wide range of species and habitat types, so the research techniques and results can be applied to many other types of anthropogenic noise.

M.E. Weisenberger et al., Effects of Simulated Jet Aircraft Noise on Heart Rate and Behavior of Desert Ungulates, 60 J. Wildlife Mgmt. 52–61 (1996).

Bernard Lohr et al., Detection and Discrimination of Natural Calls in Masking Noise by Birds: Estimating the Active Space of a Signal, 66 Animal Behav. 703–710 (2003).

S.P. Singal, Noise Pollution and Control Strategy (2005).

R.A. Fuller et al., Daytime Noise Predicts Nocturnal Singing in Urban Robins, 3 Biol. Letters 368–370 (2007).

C.K. Catchpole & Peter J.B. Slater, Bird Song: Themes and Variations (1995).

For example, the structural and temporal properties of many acoustic signals are adapted—by evolution or through individual plasticity—to maximize the propagation distance and/or minimize interference from natural noise sources. R. Haven Wiley & Douglas G. Richards, Adaptations for Acoustic Communication in Birds: Sound Transmission and Signal Detection, in 1 Acoustic Communication in Birds 131–181 (D. Kroodsma & E.H. Miller eds., 1982); H. Brumm, Signalling through Acoustic Windows: Nightingales Avoid interspecific Competition by Short-Term Adjustment of Song Timing, 192 J. Comp. Physiol. A 1279–1285 (2006); Henrik Brumm & Hans Slabbekoorn, Acoustic Communication in Noise, 35 Advances Study Behav. 151–209 (2005); Hans Slabbekoorn & Thomas B. Smith, Habitat-Dependent Song Divergence in the Little Greenbul: An Analysis of Environmental Selection Pressures on Acoustic Signals, 56 Evolution 1849–1858 (2002); G.M. Klump, Bird Communication in the Noisy World, in Ecology and Evolution of Acoustic Communication in Birds 321–338 (D. Kroodsma & E.H. Miller eds., 1996); Eugene S. Morton, Ecological Sources of Selection on Avian Sounds, 109 Am. Naturalist 17–34 (1975).

G. Patricelli & J. Blickley, Avian Communication in Urban Noise: Causes and Consequences of Vocal Adjustment, 123 The Auk 639–649 (2006); Paige S. Warren et al., Urban Bioacoustics: It's Not Just Noise, 71 Animal Behav. 491–502 (2006); Lawrence A. Rabin et al., Anthropogenic Noise and Its Effects on Animal Communication: An Interface Between Comparative Psychology and Conservation Biology, 16 Int’l J. Comp. Psychol. 172–192 (2003); Lawrence A. Rabin & Correigh M. Greene, Changes to Acoustic Communication Systems in Human-Altered Environments, 116 J. Comp. Psychol. 137–141 (2002); H. Slabbekorn & E.A.P. Ripmeester, Birdsong and Anthropogenic Noise: Implications and Applications for Conservation, 17 Molecular Ecology 72–83 (2008).

P. Marler et al., Effects of Continuous Noise on Avian Hearing and Vocal Development, 70 Proc. Nat’l Acad. Sci. 1393–1396 (1973); J. Saunders & R. Dooling, Noise-Induced Threshold Shift in the Parakeet (Melopsittacus undulatus), 71 Proc. Nat’l Acad. Sci. 1962–1965 (1974); Brenda M. Ryals et al., Avian Species Differences in Susceptibility to Noise Exposure, 131 Hearing Res. 71–88 (1999).

PTS in birds may result from sound levels of ∼125 dBA SPL for multiple impulsive sounds and ∼140 dBA SPL for a single impulsive sound. TTS can result from continuous noise levels of ∼93 dBA SPL. The term “dBA SPL” refers to the A-weighted decibel, the most common unit for noise measurements. It adjusts for human perception of sound and is scaled relative to the threshold for human hearing.

Sound levels drop by approximately 6 dB (measured using dBA SPL, or any other decibel measure), which represents a halving of loudness, with every doubling in distance from a point source, and 3 dB with every doubling of distance from a linear source, such as a highway.

Lohr et al., supra note 5.

M.A. Bee & E.M. Swanson, Auditory Masking of Anuran Advertisement Calls by Road Traffic Noise, 74 Animal Behav. 1765–1776 (2007); Henrik Brumm, The Impact of Environmental Noise on Song Amplitude in a Territorial Bird, 73 J. Animal Ecology 434–440 (2004); L. Habib et al., Chronic Industrial Noise Affects Pairing Success and Age Structure of Ovenbirds Seiurus aurocapilla, 44 J. Applied Ecology 176–184 (2007); Frank E. Rheindt, The Impact of Roads on Birds: Does Song Frequency Play a Role in Determining Susceptibility to Noise Pollution?, 144 J. Ornithologie 295–306 (2003).

J.P. Swaddle & L.C. Page, Increased Amplitude of Environmental White Noise Erodes Pair Preferences in Zebra Finches: Implications for Noise Pollution, 74 Animal Behav. 363–368 (2007).

Slabbekorn & Ripmeester, supra note 10; Brumm, supra note 15; Hans Slabbekoorn & Margriet Peet, Birds Sing at a Higher Pitch in Urban Noise, 424 Nature 267 (2003); William E. Wood & Stephen M. Yezerinac, Song Sparrow (Melozpiza melodia) Song Varies with Urban Noise, 123 The Auk 650–659 (2006).

Patricelli & Blickley, supra note 10; Warren et al. supra note 10; Slabbekoorn & Peet, supra note 17.

Quinn found that chaffinchs (Fringilla coelebs) perceived an increased risk of predation while feeding in noisy conditions, likely due to a reduced ability to detect auditory cues from potential predators. L. Quinn et al., Noise, Predation Risk Compensation and Vigilance in the Chaffinch Fringilla coelebs, 37 J. Avian Biol. 601–608 (2006). Research on greater sage-grouse also highlights the potential for noise to contribute to predation. One of the methods for capturing sage-grouse is to mask the sound of researcher footfalls using a noise source such as a stereo or a chain saw. With such masking, the grouse can be easily approached and netted in their night roosts for banding or blood sampling. Presumably, predators would be equally fortunate in noisy areas, though the ability of predators to use acoustic cues for hunting could be diminished by masking as well.

Clinton D. Francis et al., Noise Pollution Changes Avian Communities and Species Interactions, 19 Current Biol. 1–5 (2009).

Dooling & Popper, supra note 1; N. Kempf & O. Huppop, The Effects of Aircraft Noise on Wildlife: A Review and Comment, 137 J. Ornithologie 101–113 (1996); D.K. Delaney et al., Effects of Helicopter Noise on Mexican Spotted Owls, 63 J. Wildlife Mgmt. 60–76 (1999); L.A. Rabin, R.G. Coss, & D.H. Owings, The Effects of Wind Turbines on Antipredator Behavior in California Ground Squirrels (Spermophilus beecheyi), 131 Biol. Cons. 410–420 (2006).

Weisenberger et al., supra note 4.

J.C. Wingfield & R.M. Sapolsky, Reproduction and Resistance to Stress: When and how, 15 J. Neuroendocrinol, 711 (2003); A. Opplinger et al., Environmental Stress Increases the Prevalence and Intensity of Blood Parasite Infection in the Common Lizard Lacerta vivipara, 1 Ecology Letters 129–138 (1998).

Wingfield & Sapolsky, supra note 23; S.K. Wasser et al., Noninvasive Physiological Measures of Disturbance in the Northern Spotted Owl, 11 Cons. Biol. 1019–1022 (1997); D.M. Powell et al., Effects of Construction Noise on Behavior and Cortisol Levels in a Pair of Captive Giant Pandas (Ailuropoda melanoleuca), 25 Zoo Biol. 391–408 (2006).

P. Alario et al., Body Weight Gain, Food Intake, and Adrenal Development in Chronic Noise Stressed Rats, 40 Physiol. Behav. 29–32 (1987).

Affected animals include birds, mammals, reptiles, and amphibians. Forman et al., supra note 6; Rheindt, supra note 15; Rien Reijnen et al., The Effects of Car Traffic on Breeding Bird Populations in Woodland. III. Reduction of Density in Relation to the Proximity of Main Roads, 32 J. Applied Ecology 187–202 (1995); Rien Reijnen et al., The Effects of Traffic on the Density of Breeding Birds in Dutch Agricultural Grasslands, 75 Biol. Cons. 255–260 (1996); S.J. Peris & M. Pescador, Effects of Traffic Noise on Passerine Populations in Mediterranean Wooded Pastures, 65 Applied Acoustics 357–366 (2004); R.T.T. Forman & L.E. Alexander, Roads and Their Major Ecological Effects, 29 Ann. Rev. Ecology Systematics 207–231 (1998); E. Stone, Separating the Noise from the Noise: A Finding in Support of the “Niche Hypothesis,” That Birds Are Influenced by Human-Induced Noise in Natural Habitats, 13 Anthrozoos 225–231 (2000); Ian Spellerberg, Ecological Effects of Roads and Traffic: A Literature Review, 7 Global Ecology Biogeog. Letters 317–333 (1998); David Lesbarrères et al., Inbreeding and Road Effect Zone in a Ranidae: The Case of Agile Frog, Rana dalmatina Bonaparte 1840, 326 Comptes Rendus Biologies 68–72 (2003).

See, e.g., Jeffrey A. Stratford & W. Douglas Robinson, Gulliver Travels to the Fragmented Tropics: Geographic Variation in Mechanisms of Avian Extinction, 3 Frontiers Ecology & Env’t 91–98 (2005); P. Laiolo & J. L. Tella, Erosion of Animal Cultures in Fragmented Landscapes, 5 Frontiers Ecology & Env’t 68–72 (2007).

Forman & Deblinger, supra note 3; Rheindt, supra note 15; Peris & Pescador, supranote 26; M. Kuitunen et al., Do Highways Influence Density of Land Birds? 22 Envtl. Mgmt. 297–302 (1998); A.N. van der Zande et al., The Impact of Roads on the Densities of Four Bird Species in an Open Field Habitat—Evidence of a Long-Distance Effect, 18 Biol. Cons. 299–321 (1980).

C.S. Findlay & J. Houlahan, Anthropogenic Correlates of Species Richness in Southeastern Ontario Wetlands, 11 Cons. Biol. 1000–1009 (1997).

Studies in large mammals typically find road avoidance, but many small mammals are found in higher densities near roads, due to increased dispersal and reduced numbers of predators. Forman & Deblinger, supra note 3; F. J. Singer, Behavior of Mountain Goats in Relation to US Highway 2, Glacier National Park, Montana, 42 J. Wildlife Mgmt. 591–597 (1978); G.R. Rost & J.A. Bailey, Distribution of Mule Deer and Elk in Relation to Roads, 43 J. Wildlife Mgmt. 634–641 (1979); L.W. Adams & A.D. Geis, Effects of Roads on Small Mammals, 20 J. Applied Ecology 403–415 (1983).

Reijnen et al., supra note 29; R. Foppen & R. Reijnen, The Effects of Car Traffic on Breeding Bird Populations in Woodland. II. Breeding Dispersal of Male Willow Warblers (Phylloscopus trochilus) in Relation to the Proximity of a Highway, 31 J. Applied Ecology 95–101 (1994).

N. Sarigul-Klign, D.C. Karnoop, & F.A. Bradley, Environmental Effect of Transportation Noise. A Case Study: Criteria for the Protection of Endangered Passerine Birds, Final Report (Transportation Noise Control Center (TNCC), Department of Mechanical and Aeronautical Engineering, University of California, Davis, 1977); G. Bieringer & A. Garniel, Straßenalärm und Vögel—eine kurze Übersicht über die Literatur mit einer Kritik einflussreicher Arbeiten. Bundesministerium für Verkehr, Innovation und Technologie. Schriftenreihe Straßenforschung. Unpublished manuscript, Vienna, 2010 (copy on file with the authors).

Noise is commonly measured in dBA SPL, a unit that is measured differently in different countries, making extrapolation difficult. Bieringer & Garniel, supra note 32.

Sinks are areas where successful reproduction is insufficient to maintain the population without immigration. H.R. Pulliam, Sources, Sinks, and Population Regulation, 132 Am. Naturalist 652–661 (1988).

L. Fahrig et al., Effect of Road Traffic on Amphibian Density, 73 Biol. Cons. 177–182 (1995).

Delaney et al., supra note 24; D. Hunsaker, J. Rice, & J. Kern, The Effects of Helicopter Noise on the Reproductive Success of the Coastal California Gnatcatcher, 122 J. Acoustical Soc. Am. 3058 (2007); Jennifer W. C. Sun & Peter M. Narins, Anthropogenic Sounds Differentially Affect Amphibian Call Rate, 121 Biol. Cons. 419–427 (2005).

L. Habib, E.M. Bayne, & S. Boutin, Chronic Industrial Noise Affects Pairing Success and Age Structure of Ovenbirds Seiurus aurocapilla, 44 J. Applied Ecology 176–184 (2007).

Habib et al. found an increased proportion of juveniles in noisy areas, suggesting that the area is undesirable for breeding adults. Id.

J.B. Dunning et al., Spatially Explicit Population Models: Current Forms and Future Uses, 5 Ecological Applications 3–11 (1995).

Forman, Reineking, & Hersberger, supra note 6; Reijnen et al. (1995), supra note 29; Reijnen et al. (1996), supra note 29; Foppen & Reijnen, supra note 34; R. Reijnen & R. Foppen, The Effects of Car Traffic on Breeding Bird Populations in Woodland. I. Evidence of Reduced Habitat Quality for Willow Warblers (Phylloscopus trochilus) Breeding Close to a Highway, 31 J. Applied Ecology 95–101 (1994).

Lohr et al., supra note 8; E.A. Brenowitz, The Active Space of Red-Winged Blackbird Song, 147 J. Comp. Physiology 511–522 (1982); R.J. Dooling & B. Lohr, The Role of Hearing in Avian Avoidance of Wind Turbines, in Proc. Nat’l Avian-Wind Planning Meeting IV 115–134 (S.S. Schwartz ed., for the Avian Subcommittee, National Wind Coordinating Committee, 2001).

For detailed methods on calculating masking potential, see R.J. Dooling & J.C. Saunders, Hearing in the Parakeet (Melopsittacus undulatus): Absolute Thresholds, Critical Ratios, Frequency Difference Limens, and Vocalizations, 88 J. Comp. Physiol. 1–20 (1975).

A measure of how hearing sensitivity varies with the frequency of the sound. In general, birds do not hear as well as mammals in very low or high frequencies, or use them to communicate. Dooling & Popper, supra note 1.

A measure of how much energy is present in each frequency band of the sound.

This is the difference in amplitude between signal and noise necessary for detection of the signal. For a generalized bird, the critical threshold ranges from approximately 26 to 28 dB between 2 and 3 kHz, meaning that a typical bird cannot hear a 2–3 kHz vocalization unless the vocalization exceeds the background noise in that frequency range by 26–28 dB. In general, birds have higher critical ratios than mammals, making them worse at discriminating signals in noise. If measurements for these parameters are not available for the focal species, then information from closely related species may be used as a substitute. However, this may be misleading if the species of interest has particularly strong or poor hearing capabilities relative to the substitute species. Dooling & Popper, supra note 1; Lohr et al., supra note 8; Dooling & Saunders, supra note 45.

Lohr et al., supra note 5; Brenowitz, supra note 39.

Lohr et al., supra note 5; Bee & Swanson, supra note 15; G. Ehret & H.C. Gerhardt, Auditory Masking and Effects of Noise on Responses of the Green Treefrog (Hyla cinerea) to Synthetic Mating Calls, 141 J. Comp. Physiol. A 13–18 (1980); T. Aubin & P. Jouventin, Cocktail-Party Effect in King Penguin Colonies 265 Proc. R. Soc. B 1665–1673 (1998).

This would happen when humans can detect human voices, but not discriminate the identity of the speaker or the words being said. See Lohr et al., supra note 5, for a discussion of the difference between detection and discrimination.

The ability to hear sounds is improved if they are separated spatially. M. Ebata, T. Sone, & T. Nimura, Improvement of Hearing Ability by Directional Information, 43 J. Acoustical Soc. Am. 289–297 (1968); J.J. Schwartz & H.C. Gerhardt, Spatially Mediated Release From Auditory Masking in an Anuran Amphibian, 166 J. Comp. Physiol. A 37–41 (1989).

Masking is reduced when the noise has amplitude modulation patterns that make it distinct from the signal. G.M. Klump & U. Langemann, Co-Modulation Masking Release in a Songbird, 87 Hearing Res. 157–164 (1995).

Patricelli & Blickley, supra note 10; Rabin & Greene, supra note 10; Warren et al., supra note 10; Slabbekoorn & Peet, supra note 17.

Rheindt, supra note 18.

Lohr et al., supra note 8.

Dooling & Saunders, supra note 45; K. Okanoya & Robert F. Dooling, Hearing in the Swamp Sparrow, Melospiza georgiana, and the Song Sparrow, Melospiza melodia, 36 Animal Behav. 726–732 (1988); H.E. Heffner et al., Audiogram of the Hooded Norway Rat, 73 Hearing Res. 244–247 (1994); H.E. Heffner & R.S. Heffner, Hearing Ranges of Laboratory Animals, 46 J. Am. Ass’n Laboratory Animal Sci. 20–22 (2007).

Lohr et al., supra note 8; Dooling & Saunders, supra note 45; Klump & Langemann, supra note 53; L. Wollerman, Acoustic Interference Limits Call Detection in a Neotropical frog Hyla ebraccata, 57 Animal Behav. 529–536 (1999).

Dooling & Popper, supra note 1.

Marler et al., supra note 14; Ryals et al., supra note 14; J. Syka & N. Rybalko, Threshold Shifts and Enhancement of Cortical Evoked Responses After Noise Exposure in Rats, 139 Hearing Res. 59–68 (2000); D. Robertson & B.M. Johnstone, Acoustic Trauma in the Guinea Pig Cochlea: Early Changes in Ultrastructure and Neural Threshold, 3 Hearing Res. 167–179 (1980).

Swaddle & Page, supra note 19.

J. Cynx, et al., Amplitude Regulation of Vocalizations in Noise by a Songbird, Taeniopygia guttata, 56 Animal Behav. 107–113 (1998); Marty L. Leonard & Andrew G. Horn, Ambient Noise and the Design of Begging Signals, 272 Proc. R. Soc. B 651–656 (2005). This finding has been corroborated with studies of birds in the field in Brumm, supra note 18.

Dooling & Saunders, supra note 45; Klump & Langemann, supra note 53; Wollerman, supra note 53; J.B. Allen & S.T. Neely, Modeling the Relation between the Intensity Just-Noticeable Difference and Loudness for Pure Tones and Wideband Noise, 102 J. Acoustical Soc. Am. 3628–3646 (1997).

Lohr et al., supra note 8. For other studies that introduce anthropogenic noise, see Weisenberger et al., supra note 7; Bee & Swanson, supra note 18.

T. Caro, J. Eadie, & A. Sih, Use of Substitute Species in Conservation Biology, 19 Cons. Biol. 1821–1826 (2005).

Delaney, et al., supra note 24; P. R. Krausman, et al., Effects of Jet Aircraft on Mountain Sheep, 62 J. Wildlife Mgmt. 1246–1254 (1998); A. Frid, Dall's Sheep Responses to Overflights by Helicopter and Fixed-Wing Aircraft, 110 Biol. Cons. 387–399 (2003).

Sun & Narins, supra note 39; A.L. Brown, Measuring the Effect of Aircraft Noise on Sea Birds, 16 Env't Int’l 587–592 (1990).

Weisenberger et al., supra note 7; Sun & Narins, supra note 39; Leonard & Horn, supra note 62; Brown, supra note 67.

J.W. Connelly et al., Conservation Assessment of Greater Sage-Grouse and Sagebrush Habitats, Western Association of Fish and Wildlife Agencies. Unpublished Report. Cheyenne, Wyoming, 2004. Copy online at http://www.ndow.org/wild/conservation/sg/resources/greate_sg_cons_assessment.pdf

M.J. Holloran, Greater Sage-Grouse (Centrocercus urophasianus) Population Response to Natural Gas Field Development in Western Wyoming (2005) (unpublished Ph.D. dissertation, University of Wyoming) (accessible online from http://www.sagebrushsea.org/th_energy_sage_grouse_study2.htm); Brett L. Walker et al., Greater Sage-Grouse Population Response to Energy Development and Habitat Loss, 71 J. Wildlife Mgmt. (2007); Dooling & Popper, supra note 1.

Other factors at work include habitat loss, fragmentation, dust, air pollution, and West Nile virus. Connelly et al, supra note 64; Holloran, supra note 70; D.E. Naugle et al., West Nile Virus: Pending Crisis for Greater Sage-Grouse, 7 Ecology Letters 704–713 (2004).

Paired leks have similar size and location and are visited by researchers for counts on the same days. Noise is introduced at 70 dBF SPL (unweighted decibels) at 16 meters using three to four battery-powered outdoor speakers. This is similar to noise levels measured at ¼-mile from drilling rigs and main haul roads in Pinedale, Wyoming. Control leks have dummy speakers and are visited for “battery changes” with the same frequency as experimental leks.

Patricelli & Blickley, supra note 13; Warren et al., supra note 13; Rabin et al., supra note 13; Rabin & Greene, supra note 13; Slabbekoorn & Peet, supra note 20.

See, e.g., Wasser et al., supra note 27.

Most anthropogenic noise sources are very large, and it is extremely difficult to replicate loud noise over a large area from small speakers, since amplitude (and thus propagation) is limited by source size. This challenge is even greater when speakers are powered by batteries in remote field locations.

Connelly et al., supra note 69.

Noise can be reduced structurally by using alternative materials and architecture, such as noise barriers, to reduce sound production and propagation.

Noise can be reduced operationally through limitations on the timing and frequency of noisy activities, for example, by avoiding shift changes that occur at 7:00 a.m., in the peak lekking hours of sage-grouse.

Forman, Reineking, and Hersberger, supra note 6.

Dooling & Popper, supra note 1; Singal, supra note 9.

A single noise standard, for example, might establish a maximum acceptable noise level of 49 dBA at a one quarter mile from a noise source.

B.L. Southall, A.E. Bowles, & W.T. Ellison, Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendations, 125 J. Acoustical Soc. Am. 2517 (2009). There is no equivalent set of recommendations for terrestrial animals.

Department of Evolution and Ecology, University of California, Davis, CA 95616, USA. E-mail: [email protected]

Department of Evolution and Ecology and Center for Population Biology, University of California, Davis, CA 95616, USA. E-mail: [email protected]. For helpful discussion both authors thank Tom Rinkes, Sue Oberlie, Stan Harter, Tom Christiansen, Alan Krakauer, Geoffrey Wandesforde-Smith, Paul Haverkamp, Margaret Swisher, Ed West, Dave Buehler, Fraser Schilling, and the UC Davis Road Ecology Center. Research funding is acknowledged from UC Davis, the U.S. Bureau of Land Management, National Fish & Wildlife Foundation, Wyoming Sage-Grouse Conservation Fund (Wind River/Sweetwater River Basin, Upper Green River, and Northeast Sage-Grouse Local Working Groups), and the Wyoming Community Foundation Tom Thorne Sage Grouse Conservation Fund.