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HomeMy WebLinkAboutAppendix EAPPENDIX E: Revised Disturbance Analysis for Marbled Murrelet (This page intentionally left blank) Revised In -Air Disturbance Analysis for Marbled Murrelets Emily Teachout, Washington Fish and Wildlife Office DRAFT: March 26, 2015 (Updates June 18, 2012 version with corrected references and grammatical edits) Introduction Upon renewal of several U.S. Forest Service programmatic biological opinions in 2012, we revisited the analysis of effects of disturbance to nesting marbled murrelets that was contained in Appendix 1 of USFWS (2003), and titled: "Estimates of distances at which incidental take of murrelets and spotted owls due to harassment are anticipated from sound -generating, forest -management activities in Olympic National Forest." Appendix 1 documented our rationale for analyzing the in -air noise and visual disturbance effects of a variety of actions. Due to advances in our understanding of noise analysis and availability of more recent research on disturbance, we undertook an effort to update the approach presented in Appendix 1. We recognize three primary challenges with applying the approach in Appendix 1. The first is that it presents thresholds specific to type of stimuli such as "sound -only", "visual", and "combined". This assumes an ability to separate an animal's response to either auditory or visual stimuli. This is very difficult, as one must characterize the degree to which a noise source is visible to an animal (Pater et al. 2009, p. 793). Secondly, the approach relies on predicting an animal's response as a function of distance from a noise source, which is difficult because received sound levels are highly variable due, in part, to sound -propagation conditions in the field (Pater et al. 2009, p. 793). Lastly, much of the literature used in the earlier analysis is not applicable to development of a sound -only threshold, as the authors did not describe their sound metrics in enough detail to allow comparison (Teachout pers. comm. 2012). There is growing awareness of the importance of using appropriate metrics and methodologies in sound measurement and analysis (Pater et al. 2009, p. 788; Grubb et al. 2010, p.1283). In revisiting the literature cited in Appendix 1, we found that, although some of the papers have information that is applicable to the overall discussion of disturbance, they were not directly applicable to developing sound -only thresholds for these purposes. Only one paper, Delaney (1999), included defined and reliable sound metrics While Delaney (1999) does identify some responses of Mexican spotted owls to sound -only stimuli, it is unclear whether those results may have been confounded by the subject animals' ability to associate those sounds with humans that were earlier seen placing equipment. Delaney et al. (1999, p. 72) stated: "Although chainsaws were ... operated out of sight ... field crews had to set up recording equipment beneath the spotted owls... Subsequent chain saw operations may have been associated more with this ground-based human activity." As such, there is not currently enough information to develop a sound -only threshold, and we assume for the purposes of this analysis, that information on the response of murrelets to disturbance includes components of both auditory and visual stimuli. Herein, we present a revised approach that groups stressors and assumes that there may be a visual component to each of these exposures. The stressors are grouped as follows: a) Aircraft noise (helicopters and planes) b) Ground-based continuous noise and human activity (e.g., chainsaws, heavy equipment) c) Impulsive noise (impact pile driving and blasting) Any acoustic analysis needs to consider relevant aspects of the sound source, the receiver, and the path along which the sound is transmitted (Pater el al. 2009, p. 788). Use of appropriate sound metrics is necessary to relate responses to an animal and to maximize the utility of the results. For example, if a sound is comprised of frequencies outside of the range of what the animal of interest can detect, a response is less likely (Grubb et al. 2010, p. 1283). If the range of frequencies of a particular sound is not reported, it is difficult to assess where it might overlap with the hearing range of the animal of interest. Appropriate sound metrics are designed to best represent a particular sound type (i.e., continuous vs. impulsive) and should account for the frequencies within the hearing range of the species of interest (Pater et al. 2009, p. 789). We group stimuli by the type of sound produced so that appropriate metrics can be applied for both pre -project assessment and eventual monitoring and reporting. Behaviors Constituting Harassment A disturbance is event is considered significant when project activity causes a murrelet to delay or avoid nest establishment, flush away from an active nest site, or abort a feeding attempt during incubation or brooding of nestlings. A flush from a nest site includes movement out of an actual nest, off of the nest branch, and away from a branch of a tree within suitable habitat during the nesting season. Such events are considered significant because they have the potential to result in reduced hatching success, fitness, or survival of juveniles and adults. Noise and visual disturbance that causes an adult murrelet to abort a prey delivery to the nestling creates a likelihood of injury for the adult through an increased energy cost, and by exposing the adult to an increased risk of predation. Hull et al. (2001, p. 1036) report that murrelets spend 0.3 to 3.5 hours per day (mean 1.2 ± 0.7 hours per day) commuting to nests during the breeding season. The distance traveled between the nest site and foraging areas ranged from 12 to 102 km, creates a substantial energy demand for the adults. Each flight to the nest is energetically costly, increases the risk of predation from avian predators, and detracts from time spent in other activities such as foraging (Hull et al. 2001, p. 1036). Increases in prey capture and delivery efforts by the adults results in reduced adult body condition by the end of the breeding season, and increases the predation risks to adults and chicks as more trips inland are required (Kuletz 2005, pp. 43-45). If an adult would conduct a single feeding, and that feeding is aborted, and it later returns with another prey item the same day, its time spent commuting would increase by 100%, and on days when the adult would make two feeding roundtrips, commute time would increase by 50%. Ralph et al. (1995, pg. 16) state, "Predation on adult murrelets by raptors occurs in transit to nest sites ... Given the small number of nest sites that have been monitored, observations of the taking of adult murrelets by predators raises 2 the possibility that this is not a rare event." They list several observations of raptors killing adult murrelets and of murrelet wings and bones being found in peregrine falcon (Falco peregrinus) nests. An aborted feeding significantly increases an adult murrelet's time airborne, creating a likelihood of injury from predation. Sound Metrics A sound metric is a measureable parameter used to characterize and quantify a sound event (Pater et al. 2006, p. 789). A metric designed to measure continuous sound may not adequately characterize an impulsive sound such as an explosive or impact pile driving and vice versa. Care is warranted, in describing sounds and their effect on wildlife, to most accurately predict animal responses. Anthropogenic sound must be meaningfully quantified or the predicted responses will be of little utility and the results of an analysis will not be applicable to any other situation. An appropriate metric is one that measures the characteristics of a stimulus in a way that can be related to the response of an animal (Pater et al. 2009, p. 789). Based on our review of the literature and on input we received from acousticians (Laughlin pers. comm. 2012), we conclude that LEQ is an appropriate metric for chainsaws and other construction -generated sounds. For continuous sounds, an average sound level is the most appropriate way to characterize the sound (Pater et al. 2009, p. 789). One applicable metric is the LEQ measured over a specified time period (e.g., 1 second, 24 hours, etc.) (Pater et al. 2009, p. 789). The duration of the measurement period varies depending on the characteristics of the event being measured, and should always be reported as part of the measurement. For example, for vibratory pile driving a 10 -minute LEQ or 10 -minute rms is typically reported (Laughlin, 2010). For highly variable or transient sounds, simple measurement of LEQ is not appropriate. For sound events of a few to several seconds (e.g., pass -by vehicle traffic or aircraft), the choice of measurement period duration is important. In these situations, it is best to divide the event duration into short (typically 1 -second) increments. The LEQ is measured during each increment, and then the maximum value occurring in any time increment is reported. Total duration of the event should also be reported (Pater et al. 2009, p. 789). Short duration transient or impulsive sounds (<1 second) are complex, so a simple measure of average sound level is not adequate (Pater et al., 2009, p. 789). Sound exposure level (SEL) is a metric that is often used to characterize very brief events such as blasts, gunshots, and impact pile driving (Pater et al. 2009, p. 790). However, there is little information available on the behavioral response of animals to impulsive sound described relative to SEL. As such, until more information is available, we currently rely on observed response distance for estimating potential behavioral responses from impulsive sound. Exposure Human activities occurring in, or near, suitable murrelet nesting habitat, expose murrelets to a variety of stressors. This analysis is limited to those stressors associated with "disturbance" that result from a combination of noise and visual stimuli. Human activities considered in this analysis are those typically occurring with activities such as transportation system maintenance, maintenance of infrastructure that supports recreational activities, and forest management. Specific activities may include timber harvest and hazard tree removal, road and trail maintenance, and bridge repair. Equipment that may be used to conduct these activities includes chainsaws, aircraft, heavy equipment, and impact pile drivers. To estimate the expected response of murrelets to these exposures we grouped them as follows: aircraft (helicopter and small planes), ground-based human activity (e.g., chainsaws, heavy equipment), and impulsive sound (impact pile driving and blasting). Exposure to Aircraft (Helicopter and Small Plane) Activities The sounds of aircraft are rich in low -frequency energy, and travel long distances efficiently (Pater et al. 2006, p. 792; Grubb et al. 2010, p. 1280). The highest levels of sound energy produced by helicopters are below 100 Hz (Grubb et al. 2010, p. 1280), which is well below the best hearing sensitivities of most birds (Dooling and Popper 2007, p. 21). Further, much of the sound energy from aircraft is at frequencies below those that most birds can detect (Grubb et al. 2010, p. 1281; Dooling and Popper 2007, p. 21). Grubb et al. (2010) present sound level for four helicopter models (Table 1 in Grubb et al. 2010, p. 1277). The ranges in A -weighted SEL were: Table 1: SELs for four helicopter models (rounded to nearest dB). Helicopter Model dBA SEL Overhead dBA SEL at 100 m AH -64 Apache 95-99 88-97 Eu rocopter AS350 B3 86-89 85-85 Eurocopter EC130-B4 83-84 82-82 Bell 206 L4 87-91 85-89 Potential Response to Aircraft Activities A few studies have examined raptor responses to aircraft, and these note that flush rates were higher if raptors were naive (Platt 1977, pp. 36, and 55) and a majority flushed at <_50 meters (Grubb et al. 2010, p. 1282). During incubation, diurnal raptors such as osprey (Pandeon holioetus) (Carrier and Melquist 1976, p. 79), red-tailed hawks (Buteo jamaicensis) (Craig and Craig 1984, p. 24), bald eagles (Halieetus leucocephalus) (Fraser et al. 1985, p. 585) and Mexican spotted owls (Strix occidentalis lucida) (Delaney et al. 1999, p. 60) appear reluctant to flush. Grubb et al. (2010) conducted an extensive study of the response of golden eagles to four models of helicopters and concluded that no special management restrictions were required for heli -ski operations (p. 1283). There were no significant responses or detrimental effect to nesting success even with what are considered large helicopters (Apache AH -64) (p. 1282). The study recorded 303 helicopter passes at 22 nesting territories. Nest success, productivity, and rates of re -nesting in the following year, were not reduced. No flushes were observed during incubation and three flushes were observed, though the authors note that these might have been imminent departures that were precipitated rather than a startle or avoidance response (p. 1275). 4 Delaney (1999) studied response of Mexican spotted owls to helicopters and found that they did not flush when SELs were _<92 dBA. They concluded that helicopter sounds below this level should not detrimentally affect spotted owls (p. 74). The farthest distance that helicopter elicited a flush response was 89 m. During a study of radio -tagged murrelets in British Columbia, helicopters were used to locate the incubating adults by circling and hovering over nest sites. The hovering and circling came within 100- 300 meters of the nest and lasted approximately three minutes. None of the radio -tagged adults incubating any of the nests (n = 125) flushed (R. Bradley, Univ. BC, 2002, pers. comm. in USFWS 2003, p. 278). Long and Ralph (1998, p. 18) noted that murrelets did have an observable response to either airplanes or helicopters flying overhead, except when they passed at low altitude. One chick did not respond to an airplane passing twice within 0.25 mile at 1,000 ft, but another chick lay flat on the branch "when an aircraft passed at low altitudes" ("low altitudes" was not defined) (Long and Ralph 1998, p. 18). Expected Response to Aircraft Activities The likelihood of an animal responding to a particular sound is related, in part, to whether or not the frequencies contained in the sound are within their hearing range. This was observed by Grubb et al. (2010) when they found that golden eagles were not disrupted by helicopter noise, potentially because most of the sound energy is below their auditory threshold (p. 1275, p. 1283). We assume that marbled murrelets have hearing sensitivities similar to most other birds and, as a result, the majority of the sound energy from aircraft is likely to be below their best sensitivities and, possibly below the frequency range that they can detect. We therefore expect sounds from aircraft will either need to be of very high amplitude (>90 dBA SEL) or have a highly visible approach for murrelets to respond. During incubation, we do not expect marbled murrelets to flush in response to aircraft based on studies of other species as described by Grubb et al. 2010; Craig and Craig 1984; Fraser et al. 1985; and Delaney 1999, and based on observations of marbled murrelets (R. Bradley, Univ. BC, 2002, pers. comm. in USFWS 2003; and Long and Ralph 1998). We expect that marbled murrelets may abort or delay feedings in response to exposure to aircraft at sound levels exceeding 92 dBA SEL based on observed response of Mexican spotted owls to helicopters (Delaney 1999, entire). Adult murrelets conducting an incubation exchange or delivering a prey item may altertheir behavior in response to aircraft. We expect that nestlings will respond to approach by aircraft by lying flat on the nest branch. Exposure to Ground-based Activities Ground-based activities addressed here include activities such as transportation system maintenance, maintenance of infrastructure that supports recreational activities, and forest management. Specific activities may include timber harvest and hazard tree removal, and road and trail maintenance. This section does not address operation of roads (i.e., consistent traffic noise), or extremely loud or impulsive noises. We group these activities in this analysis in the category of ground-based human activities because we expect that responses of murrelets to these types of activities involve components of both auditory and visual stimuli. Potential Response to Ground-based Activities In response to ground-based human activity, adult murrelets have delayed and aborted feedings (Hamer and Nelson 1998, p. 11, p. 17; Long and Ralph 1998, p. 16, p. 21), diverted their flight paths (Hamer and Nelson 1998, p. 17), delayed entry to nesting habitat (Hamer and Nelson 1998, p. 12), and vacated suitable habitat (E. Burkett, pers comm.). Chicks have responded to human presence by assuming defensive postures (Binford et al. 1975; p. 307; Long and Ralph 1998, p. 16; Simons 1980, p. 4). There are a number of studies on how disturbance affects a variety of birds (see USFWS 2006). Multiple studies on bald eagles (e.g., Knight and Knight 1984, McGarigal et al. 1991, Stalmaster and Kaiser 1997), for example, recommend limiting activities beyond 250 meters to reduce threats from visual disturbances. Hayden and Bednarz (1991) studied the effects of human disturbance on great -horned owls (Bubo virginianus), Swainson's hawks (Buteo swainsoni), and Harris' hawks(Parabuteo uncinctus) in New Mexico. They found that approaches by humans flushed great horned owls at a mean distance of 65 m during incubation, and at a mean distance of 126 m during brood -rearing (p. 53). All three species fled from nest sites with greater distances of human approach during brood -rearing then during incubation (p. 53). The authors concluded that overall effects to reproductive success were subtle. Productivity was lower in human -disturbed areas during years when prey populations were depressed but these results were not statistically significant (p. 66). However, they recommended that for ease of implementation, to be inclusive of all three species' responses, and to minimize potential effects during years when prey availability was low, a 500 m buffer zone should be applied (p. 64, p. 87). It is worth noting, that this study was done in an arid, open landscape where presumably, the detectability of approaching pedestrians is greater than in a forested landscape. Delaney et al. (1999) evaluated the effects of chainsaw operation and helicopters on Mexican spotted owls and found that chainsaws elicited a greater flush response rate than helicopters at comparable distances and noise levels. They found that owls did not flush when noise stimuli were >105 m. When helicopter sound levels were _<92 dBA SEL, and when chainsaw noise was 546 dB LEQ, the authors did not observe any flushes of Mexican spotted owls. Building off this work, Delaney and Grubb (2001, entire) used those thresholds (>105 meters or >46 dBA LEQ) to predict potential flush responses to motorcycles. Delaney (1999, p. 66, p. 71) and Delaney and Grubb (2001, p. 11) note that ground-based disturbance may have a greater effect than aerial disturbance on nesting success. Long and Ralph (1998, p. 20) concluded that pedestrians had the greatest impacts to nesting birds, especially when there were no visual barriers between people and nests. Due to the difficulties locating, and then monitoring, marbled murrelet nests, there are no peer- reviewed, published articles providing empirical evidence on disturbance of marbled murrelets. We rely, instead, on observations by murrelet researchers in the field. One of the earliest and most detailed descriptions of murrelet response to disturbance came with the inadvertent discovery of a ground nest of marbled murrelets in Alaska (Simons 1980). The exposed location and ease of access allowed for observation in closer proximity than tree nests typically provide. The observer discovered the nest• during incubation and monitored it closely until near fledging. The observer noticed that the incubating adults appeared to be extremely alert and exhibited "keen hearing and sight and responded to the slightest disturbance" (p. 3). Further, he noted that, "Even a very faint unfamiliar noise would cause them to become agitated. On several occasions, my shuffling or the click of a camera shutter caused them to sit up erectly as if about to fly, looking cautiously from side to side for the source of the noise" (p. 3). Additionally, Simons (1980) noted that the newly hatched chick was very alert and seemed to have well- developed vision and hearing. It responded immediately to unusual sounds and would detect the observer's approach at over 10 meters (p.4). Overall, he characterized the murrelets as having "...extremely keen senses, alertness, and rapid flushing and flight behavior." (p. 6). Visual stimuli appear to be important as murrelets have successfully delivered prey items while researchers were in a nest tree, but were hidden from view (Hamer pers. comm. in Long and Ralph 1998, p. 16). Researchers approaching within a few meters of a nest caused delayed or aborted feedings (Hamer and Nelson 1998, p. 19), and triggered defensive postures and behavior in nestlings (Long and Ralph 1998, p. 16; Simons 1980, p. 4). Hamer and Nelson (1998, p. 11) report that a ground observer who moved from being out of sight to 35 meters away from the base of a nest tree caused a murrelet that was attempting to feed its chick to drop its fish and fly away. The same adult returned 1 hour 21 minutes later and fed the chick, although it took a different flight path to the nest. A radio -tagged male murrelet entered a stand of suitable habitat in Big Basin State Park three mornings in a row. On the third morning, he landed on a branch, when people arrived in a car, slammed the car doors, and talked loudly within 30 meters of the tree. The murrelet vocalized and then flew with another murrelet from limb to limb before they both flew from the stand. The male was preyed upon by a peregrine falcon (Falco peregrinus) later that day (E. Burkett, Cal. Dept. Fish and Game, pers. comm. In USFWS 2003, p. 270), so it is unknown whether he would have nested there. Adult murrelets in nest trees located 10 meters and 25 meters from heavily used hiking trails and three nests overhanging a trail used by 25,000 visitors per year "rarely showed behavior suggesting agitation from human presence or noise" or showed "no visible reaction to loud talking [or] yelling ... near the nest tree" (Singer 1991 in Long and Ralph 1998, p. 17). However, two perched murrelets were observed to flush from a branch 10 meters away from pedestrians (E. Burkett, Cal Dept. of Fish and Game, pers. comm., in USFWS 2003, p. 270). In their review of disturbance observations at active nest sites in Oregon and Washington, Hamer and Nelson (1998, p. 9) reported that human activity caused adult murrelets to abort nest visits or flush from the nest a large proportion of the time. Human presence around nest trees caused birds to abort feedings or flush from the nest limb. A person walking under a nest tree when an adult was on the nest limb resulted in flushing the adult off the nest limb before feeding could take place. Reactions by adults were not observed when human were out of sight (p. 17). At the Little Rackheap nest (Oregon) (located 9.9 meters off the ground), the presence of observers standing on the road within 15 m of the nest tree appeared to have an impact on whether adults would land at the nest during the pre -egg -laying period. Once observers moved off the far edge of the road and into the brush (5-10 meters farther away), the birds would land at the nest on their next flight up the road (p. 12). Twenty-seven percent of the time (n = 30) that people walked within 40 meters of a nest near a busy state highway, the adults aborted nest visits or flushed (p. 9). A researcher in an active nest tree on the Siuslaw River caused an adult to flush while attempting to deliver a fish. The adult flushed from the tree and flew off with the fish. The researcher hid behind the trunk of the tree and the adult returned minutes later, landed on the branch and successfully fed the young (p. 19). Adult murrelets also aborted feedings due the presence of automobiles traffic on the road (p. 17). One or more vehicles passing a nest caused adults to abort a nest visit (p. 9). A pickup driving down the road as two murrelets were flying above canopy height caused the murrelets to veer away and then they were no longer seen (p. 12). Heavy equipment operation on a road adjacent to suitable habitat appeared to cause murrelet detections to cease when they had previously been frequently observed (p. 12). Hamer and Nelson (1998, p. 21) noted that nest disturbances that shorten or interfere with feeding interchanges could be detrimental to young birds. They recommended a 125 -meter buffer to allow for machinery (vehicles and chainsaw) noise to reach ambient noise levels, and a 150 m buffer for any type of blasting (p. 19). The researchers recommend that the first concern in protecting nesting habitat from disturbances should be to visually screen any disturbances near areas where birds are nesting (p. 20). As described above, Hamer and Nelson (1998) observed various responses of adult murrelets to noise and human activity. However, Hebert and Golightly (2006) documented few overt responses of nesting murrelets to chainsaw noise and the presence of people hiking on trails in Redwood National and State Parks in northern California. They conducted chainsaw disturbance tests for 15 -minute intervals at a distance of 25 meters from the base of occupied nest trees (n = 12). Adult and chick responses to chainsaw noise, vehicle traffic, and people walking on forest trails resulted in no flushing and no significant increase in corvid presence (pp. 35-39). However, adults exposed to chainsaw noise spent more time with their head raised, and their bill up in a posture of alert, vigilant behavior. When undisturbed, adult murrelets spent 95 percent of the time resting or motionless. Many adult murrelets exposed to an operating chainsaw ultimately experienced complete nest failure, but the authors caution that the relationship, if any, between the disturbance trials during the incubation period and fledgling success was unclear. They concluded that reproductive success was similar for control (13 percent) and experimental nests (30 percent) (p. 37). Hebert and Golightly (2006) suggest that the behaviors they observed are similar to those of an adult murrelet reacting to the presence of a nest predator (p. 35), and that prolonged noise disturbance at nest sites could produce short term behaviors that have unknown consequences (p. 37). It is reasonable to assume that a murrelet responding to a noise by moving or shifting position would increase the chance that it will be detected by a predator. Additionally, the energetic cost of increased vigilance to protracted disturbance could have negative consequences on nesting success (p. 37). Adult murrelets feed their chicks throughout the day. Operating chainsaws while an adult approaches a nest to feed a chick may cause sufficient disturbance to result in abortion or delay of the feeding. The authors 8 estimated that a single missed feed could deprive the chick of 25-50 percent of its daily energy and water intake, which could have a significant negative impact on fledging success (p. 38). As murrelet chicks grow rapidly compared to most alcids, gaining 5-15 g/day during the first nine days (Nelson and Hamer 1995a, pg. 60), missed feedings may pose a comparatively greater risk. In general, murrelets make multiple trips to a nest to deliver prey items, and they sometimes spend a considerable amount of time at the nest site during these prey deliveries. The combination of adults making multiple trips and amount of time spent at the nest site increases the likelihood that normal feeding activity could be disrupted. Based on a compilation of radio -telemetry data we several feedings occur during the mid-day portion the nestling phase (USFWS 2012). Murrelets sometimes take up to an hour at the nest when delivering a prey item. Given the number of feedings and the amount of time an adult murrelet spends at the nest, the minimum percent time per midday period an adult would be in a forest stand attempting to feed its nestling would be 1 percent (using 12 hours in midday, 1 feeding per midday, 7 minutes per feeding) and the maximum percent would be >100% (using 8.5 hours in midday,10 feedings per midday,1 hour per feeding). A reasonable worse -case scenario would be 58 percent (using 9 hours in midday, 7 feedings per midday, 45 minutes per feeding). A reasonable worse - case scenario indicates that, in an occupied murrelet stand, we would expect that one adult per nest could be present any time during the day. Therefore, there is a reasonable likelihood that the types of activities addressed here would intersect with a prey delivery attempt at some point during each day in the nestling phase. Nestlings appear more tolerant to potential disturbance than do adult murrelets. Nestlings did not have a noticeable response when researchers were within 6-35 m and they appeared to habituate to researchers changing camera batteries within 1 m (Long and Ralph 1998, p. 16). A nestling videotaped during chainsaw operation within 40 m of the nest tree dozed, preened, and stretched, and had no observable reaction to the activity (P. Hebert, Cal. Dept. Fish and Game, pers. comm. in USFWS 2003, p. 269). Hebert and Golightly (2006) did not find a statistically significant difference in the responses of murrelet chicks exposed to chainsaw noise compared to pre- and post -disturbance trials (p. 36). All three chicks exposed to chainsaw disturbance fledged (p. 29). Hebert and Golightly (p. 36) conclude that chainsaw noise disturbance lasting 10 to 15 minutes at a distance greater than 25 m from the nest does not appear to induce long-term behavioral changes. Expected Response to Ground-based Activities Based on the above information, we expect that adult murrelets may respond to ground-based activities such as chainsaw operation, sudden noises, traffic, heavy equipment operation, and human presence within nesting habitat, and that these responses will be strongly influenced by visual clues. Of these, we expect that activity involving human approach in nesting habitat will have the most severe response. The range of potential responses could include delay or avoidance in nest establishment, flushing from a nest, and aborting or delaying a feeding attempt. We expect that adult murrelets are most likely to exhibit a flush response during nest establishment and while attempting to deliver food to the nestling. We assume that disturbance activities that occur in close proximity to occupied stands are expected to result in these reactions. Adult murrelets that are incubating an egg are not expected to flush from disturbance. Short-term ground-based disturbance 9 events (such as operating a chainsaw for 15 minutes or less) do not appear to cause a measureable effect to murrelet adults or chicks. Murrelet chicks appear to be mostly unaffected by noise and human activity. The greatest risk to murrelet chicks from disturbance is the potential for missed feedings during the mid-day period (assuming a limited operating period restricting dawn/dusk activity). We do not expect nestlings to flush in response to ground-based activity based on observations by Long and Ralph (1998) and P. Hebert (California Fish and Game, pers comm. cited in USFWS 2003). We screened the available information on disturbance by those that provided adequate description of sound metrics to allow for careful interpretation and comparison of the results. We found there is insufficient information to distinguish between a murrelet's response to visual vs. auditory stimuli presented with ground-based disturbance. We assume that murrelet response to ground-based disturbance results from components of both stimuli. Predicting an animal's response solely as a function of distance from a noise source is difficult, and may be inaccurate, because a received sound level will vary substantially due to propagation conditions in the field (Pater et al. 2009, p. 793). Coupled with a lack of empirical evidence on cause -and -effect relationships between ground-based disturbance and murrelet response, we believe it's appropriate to use a standardized buffer width beyond which we do not expect murrelets to flush from a nest or abort or delay a feeding. Documented response ranges to these activities by forest -nesting birds extend to greater than 100 meters and researchers who have studied murrelet response to disturbance in the field recommend disturbance buffers of greater than 100 meters (Hamer and Nelson 1998). Documented responses of marbled murrelets to ground-based activities have not extended to 100 m, but rigorous studies have not been done and only a small number of occupied nests have been monitored. In summary, we do not expect ground-based activities to result in significant behavioral responses in chicks, but we do expect significant responses by adults. Adults are expected to respond negatively to human disturbance when they are establishing nest sites and during prey deliveries. Due to the number of trips adult murrelets may make to nest sites, and given the amount of time they spend at the nest during a prey delivery, it is reasonable to expect that these activities will intersect with murrelet occurrence in suitable habitat during the nesting season. There is considerable overlap in the various phases of nest chronology, making it difficult to identify specific periods when responses may differ. Though there appears to be a lower risk of adults flushing during incubation, there is enough variation and overlap in nest establishment, incubation, and hatching periods that management requirements specific to those periods are not feasible without detailed, site-specific, information. Therefore, we assume there is equal risk and similar responses to these exposures throughout the nesting season. We conclude that these responses are reasonably likely to occur within 100 meters of ground-based activity. Exposure to Impulsive Sound -Generating Activities Impulsive sound -generating activities addressed in this analysis include impact pile driving and blasting. Impact pile driving may be used for activities such as bridge repair and bank stabilization. Blasting may be used for activities related to road construction. 10 Impulsive sound may be more disruptive than continuous sounds due to the associated noise levels and/or the concussive nature of the sounds (Schueck et al. 2001, p. 613). At levels less than 140 dBApeak, impact noise such as pile driving behaves similarly to impulse noise from blasting (Hamernik and Hsueh 1991, p. 189). Like aircraft, sounds of explosions and large guns are rich in low -frequency energy and consequently travel long distances efficiently (Pater et al. 2009, p. 792). Impact pile driving creates a short, repetitive broad -band sound with relatively high amplitudes. Sound from impact pile driving will vary depending on the type of equipment, type of pile (e.g., steel vs. wood), substrate type and a variety of other factors. For this analysis, we consider the potential noise levels from impact installation of steel piles to pose the greatest risk for disturbance. Potential Response to Impulsive Sound -Generating Activities Impulsive sounds are generated by activities such as impact pile driving and blasting. There is very little information on the response of birds to impulsive noise (Dooling and Popper 2007, p. 27). A review compiled by Dooling and Popper (2007, p. 25) indicates that birds exposed to an impulse (e.g. a blast) of noise of at least 140 dBA SPL, or exposures to multiple impulses of noise at 125 dBA SPL are likely to suffer hearing damage. These data are largely from laboratory experiments with budgerigars (Melopsittacus undulates) exposed to short bursts (<10 ms) of pure -tone sounds (Hashino et al. 1988, p. 2540). Other than noting that these exposures were A -weighted SPLs, a metric was not given. Until more information is available, we assume that these levels are the highest observed rms levels. Individual Impulsive Sound Events (e.g., Blasting) There is only limited information regarding sound levels associated with various types of blasting (USFWS 2003, pp. 276-277). The sounds produced by blasting are highly variable and dependent on the size and type of charge, the material being blasted, and whether noise minimization techniques are employed (MM&A 2008, p. ii). Holthuijzen et al. (1990, p. 272) reported sound levels for small, experimental blasts using 0.37 Ib charges of Kinestek and 1.1 Ib. charges of dynamite. Surface (uncovered) charges were detonated at a distance of 100 m from the sound measuring equipment in an open area. Peak noise levels averaged 140 dBA rms (range = 138 —141 dBA) for Kinestek and 145 dBA (range = 144-146 dBA) for dynamite at 100 m. A review by Dooling and Popper (2007, pp. 23-24) reports that birds exposed to noise levels 140 dBA or greater are likely to suffer hearing damage (injury). The blasts described above would be potentially injurious to birds at distances of at least 100 m (330 ft). Effects of blasting on nesting prairie falcons (Falco mexiconus) were studied at an active construction site as well as experimentally (Holthuijzen et al. 1990). Construction blasts were located 560 to 1000 m (0.34 —0.62 mile) from falcon nest sites, and experimental blasts were conducted between 120 and 140 m (394 — 459 ft) from nest sites (Holthuijzen et al. 1990, pp. 271-272). Peak sound levels measured at the nest site were 139-140 d6. The authors did not clearly identify the sound level metric they were using though they noted that it was a "peak' level. Given that it is impulsive noise it is reasonable to assume their measurements were reported in A -weighted dBpeak levels. The overall flushing rate in the experimental study (58 percent) was 4-6 times higher than those observed in the construction area (7 percent) (Holthuijzen et al. 1990, pp. 272-274). Falcons perched in the experimental study area flushed 79 percent of the time (p. 273). Incubating and brooding falcons flushed in 39 and 13 percent of the events, respectively (p. 274). There was no indication that the 11 falcons habituated to repeated exposures as birds exposed to blast noise were just as likely to flush during subsequent exposures (Holthuijzen et al. 1990, p. 274). The nesting falcons exposed to experimental blasting were ultimately successful in fledging young (Holthuijzen et al. 1990, p. 280). With maintain productivity and nest re -occupancy in subsequent years, the authors conclude that a buffer of 125 meters provided that peak noise levels do not exceed 140 dB at the nest site and that no more than 3 blasts occur on a given day or 90 blasts during the nesting season will be protective (p. 280). This level, however, was not recommended with the intent of predicting individual flush responses. Concussive Impulsive Sound Events (e.g., Impact Pile Driving and Artillery) Impact pile driving and artillery fire are similar in that they are repetitive, impulsive sounds with high amplitudes. Sound from impact pile driving will vary depending on the type of equipment, type of pile, substrate type and a variety of other factors. Typical pile types include steel, wood and concrete. Of these, steel piles generate the highest sound levels. Reported sound levels for impact pile driving projects are usually in the range of 101-110 dBA Lmax, at 50 ft from the source (FHWA 2006, section 9; WSDOT 2011, p. 7.11). Given the suggested injury thresholds of 140 dBA SPL, and 125 dBA SPL suggested by Dooling and Popper (2007) we don't expect that murrelets would be exposed to injurious sound levels from pile driving unless there was potential exposure within 50 feet (where sound pressure levels would likely be greater than 110 dBA). Schueck et al. (2001) studied the effect of military training activity on raptors and found that they were more responsive to the impulsive sounds of ammunition fire than the more continuous sounds of tank operation, perhaps due to the concussive nature of ammunition fire (p. 613). They also found that military training activities that involved artillery fire reduced prey capture attempts, and temporally and spatially altered foraging locations (p. 613). Recently, Delaney et al. (2011) studied the effect of military training activity on red -cockaded woodpeckers (Picoides borealis). This work evaluated the effect of impulsive sound from artillery simulators and firing of 0.50 -caliber blanks. It is important to consider, though, that the woodpeckers nest in cavities which not only affect the transmission of the sound (i.e., increase the received levels), but also limit the birds visibility of the stressor. However, there are a few points worth noting: the woodpeckers flushed during both the incubation and nestling phase; flush response distances extended to over 150 m; the authors characterized behavioral responses of the woodpeckers as "minimal" when stimuli were greater than 122 m; and they did not observe flush responses when stimuli were farther than 152 m. Expected Response to Impulsive Sound -Generating Activities Murrelets exposed to impulsive sound that exceeds 140 dBA SPL are likely to suffer injury in the form of hearing loss because the intensity of the noise is sufficient to damage the delicate inner ear sensory hair cells (Dooling and Popper 2007, p. 24). A partial loss of hearing sensitivity has important implications for the survival and fitness of individual murrelets. Vocal communication between murrelets is an important aspect of murrelet foraging behavior in the marine environment, and vocalizations also 12 appear to serve an important social function at inland nesting sites (Nelson 1997, pp. 9-11). Hearing ability also has important implications for predator avoidance in both marine and terrestrial habitats It is widely thought that SEL is the best metric for describing impulsive sounds. However, there is little information available on the behavioral response of animals to impulsive sound described relative to SEL. As such, until more information is available, we currently rely on observed response distance for estimating potential behavioral responses from impulsive sound. We expect that within 110 m of impact pile driving there is a reasonable likelihood of significant behavioral responses (e.g., flushing). We expect that exposure of murrelets to sound from impact pile driving could cause injury at very close distances and/or could result in flushing from exposure to concussive, impulsive, sound. For blasting events, we consider the potential disruption zone (flush response) for murrelets to be a 0.25 -mile radius around the project site. This is based on the findings of Holthuijzen et al. (1990, p. 273) which is an increase over the distance recommended to avoid productivity impacts in order to include potential flush responses. Remaining Issues This analysis does not specifically address risks to nesting murrelets posed by masking of biologically important sounds or disruption of attention. Conclusion The body of knowledge on bird response to disturbance indicates that human activity can impact nesting success and can be energetically costly to individual birds. Disturbance can have profound effects throughout the nesting season, including the nest establishment, incubation, and chick rearing phases. Marbled murrelet response to disturbance is variable and appears related to the developmental stage of the individual bird exposed to stimuli, degree of habituation existing prior to exposure, and whether there is a visual component to the stimuli. Murrelets have responded behaviorally to disturbance in ways that create a reasonable likelihood of injury to the adult, the chick, or both. This analysis groups potential exposures of nesting murrelets to noise and human activity into three categories in a manner that allows for improved comparison of available noise data and acknowledges limitations in existing information. We conclude that under certain scenarios these activities could result in significant disruptions of normal behaviors that result in a likelihood of injury to marbled murrelets. Behavioral responses that we anticipate could occur and that are considered significant are: An adult murrelet avoiding or delaying nest establishment An adult murrelet flushing from a nest or perch within the vicinity of a nest site An adult murrelet delaying or aborting one or more feedings 13 We expect that these behaviors are likely to occur when: Aircraft noise exceeds 92 dBA SEL at a nest site Ground-based activity occurs during the nesting season within 100 m of a nest site Impulsive noise from blasting within 0.25 mi of a nest site Impulsive noise from pile driving within 110 m of a nest site We expect injury to murrelets (e.g., hearing damage) to occur when in -air sound pressure levels exceed: 140 dBA SPL (single impulse) 125 dBA SPL for multiple impulses 14 Literature Cited Binford, L.C., B.G. 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