Routes, initiating Major Flying Exercises (MFEs), and increasing the size of Military Operations Areas (MOAs).  Each of these actions required a separate Environmental Impact Assessment, and all but the MOA increase were concluded with a Finding of No Significant Impact.  An Environmental Impact Statement was prepared for the proposed MOA increase, and a Record of Decision was signed in 1997 (Dept. of the Air Force 1997).  Among the changes proposed to the existing arrangement and accepted in the ROD were different boundaries for some MOAs, additional MOAs, the addition of supersonic flight to some MOAs, standard floors for some of the supersonic operations in existing MOAs, and higher numbers of aircraft authorized to participate in Major Flying Exercises (MFE). The Final EIS and the ROD included a number of mitigation measures designed to minimize negative impacts on wildlife. The ROD also established committees made up of Air Force and resource agency representatives to monitor the effectiveness of the mitigation measures. Among other needs, these committees recognized the importance of determining the effectiveness of the mitigation measures on Dall’s sheep and the need to evaluate the impacts of low-level military aircraft on Dall’s sheep.

Figure 1.  Dall’s sheep distribution and military special use airspace (MOAs) in Alaska.

Military aircraft in all MOAs may be involved in routine flying exercises or more complex MFEs.  The Final EIS (1995) and the ROD (1997) make a broad distinction between MFEs flying days and routine training days.  Routine training days are typically limited to 240 days per year due to budget constraints.  Routine training days include the routine joint and combined training as well as exercise training such as Low-Altitude Navigation and Targeting Infared for Night exercises, weapons training deployment, Air National Guard and Air Force Reserve deployments, and muti-national excercises.   MFE training days can occur no more then 60 days per year and typically include aircraft that are participating in the MFE as well as aircraft that are participating in routine training, although routine training levels are typically reduced at this time.  Characteristics that would change a routine flying exercise into an MFE would be a 50% or greater increase in the daily flying activity rate out of Eielson or Elmendorf AFBs or an increase of 50 aircraft operations per day.  However, there is no single criteria that distinguishes an MFE from a routine training exercise (Jim Hostman, US Air Force, pers. com.).  Instead, this designation is determined by a committee of exercise planners and air space managers.  MFEs typically include between 55 and 110 aircraft and aircraft of different types.  Participates typically come from numerous organizations, both national and international (Jim Hostman, US Air Force, pers. com.).  

Training exercises typically occur between 0800h and 2200h, Monday through Friday and, on average, up to 2 weekends per 3-month period.  MFEs occur Monday through Friday, 0800h through 1800h but are most concentrated between from 1000h through 1200h, and 1500h through 1700h.  Training on weekends may also occur on average of 2 weekends per quarter.  In general, 1 MFE is to take place between February and April, 4 MFEs between May and August, and 1 MFE between October and November.  A typical MFE is 10 days in duration but can last as long as 15 days.  Up to 100 aircraft a day can be involved in an MFE, with each aircraft flying up to 2 sorties (a single aircraft take-off, flight, and landing) per day for a total of 200 MFE sorties per day (Dept. of the Air Force 1995).  No MFEs are to be conducted during September, December, or January, or during the week prior to or the week after the 4^th of July.  There is a minimum interval of 2 weeks between MFEs.

The largest MFEs that occur in Alaska are termed “Cope Thunders”.  There are normally 4 Cope Thunder exercises each year and they each last approximately 2 weeks.  Air activity typically occurs during 2, 3h blocks per day and typically occurs Monday through Friday.  The most intense flying occurs during air-to-air combat training and occurs during 2, 50-minute (sometimes longer) windows per day.  MOA use is primarily in the Yukon 1, 2, 3A, and 4 MOAs (Fig. 2).  Most of the flying below 5000 feet above ground level occurs in these same 2, 50-minute windows.  An average sortie time below 5000 feet above ground level does not exceed 30 minutes.

Figure 2.  Location of Military Operations Areas (MOAs) in interior Alaska, 1998.  Within the MOA structure some areas are mitigated for potential impacts of low-level military aircraft on Dall’s sheep populations.  Two study sites were selected for studying potential impacts.  One area (Cirque Lake) is a mitigated sited and the second (West Point/Puzzle Gulch) is not.

Noise from low-level and high-level military aircraft has the potential to significantly impact ambient noise levels.  Of primary concern is the potential for flight activity overwildlife to cause physiological and/or behavioral reactions that reduce the animals’ fitness (National Park Service 1994).  The way in which animals respond to overflights  could interfere with raising young, habitat use, and physiological energy budgets (National Park Service 1994).  Effects of overflights could be either chronic or acute.  Chronic stress can compromise the general health of the animal and can be difficult to detect.  Acute responses, such as startle and panic behavior, occur in most wildlife species evaluated at noise levels greater than 95 decibels (dB) (Dept. of the Air Force 1992).  Noise events of this magnitude that are produced by military jet aircraft are typically short in duration and are essentially instantaneous events (Dept. of the Air Force 1992).  Wildlife near and under these types of overflights are unlikely to detect them until the aircraft is above or past them.  This activates the sympathetic nervous system (Moller 1978) causing a “startle” effect (Dept. of the Air Force 1992).   In interior Alaska, maximum noise levels between 73 to 118 dB can be expected from routine low-level training operations (Dept. of the Air Force 1995).

Disturbance by human activity affects wildlife by increasing the energy invested by an individual in antipredator behavior (Berger et al. 1983).  Both predation and disturbance can indirectly affect population dynamics by increasing energetic costs.  Costs may include: 1) escape behavior (running or moving to different areas), 2) reduction in foraging efficiency by increasing vigilance behavior or by forcing individuals to use habitats in which safety is greater but forage quantity and quality are reduced, 3) interruption of maintenance activity such as feeding or ruminating, 4) increased exposure to natural predators, and 5) higher heart and metabolic rates.  These costs could reduce reproductive success of individuals and lead to population declines. 

Of the studies done on other taxa, perhaps studies on bighorn sheep (Ovis canadensis) are most applicable to Dall’s sheep since they are of the same genus (Ovis spp.).  Krausman and Hervert (1983) found that bighorn sheep did not respond to overflights of a Cessna 172 or Cessna 182 above 100 m (330 feet) but would leave areas when overflown by aircraft below 50 m (165 feet).  Stockwell et al. (1991) found that in a situation with intense helicopter activity, bighorn sheep foraged less efficiently in the presence of helicopters than in the absence of helicopters.  Bleich et al. (1994) observed that bighorn sheep overflown by helicopters during wildlife surveys exhibited marked responses in movement when compared to undisturbed animals.  In addition, they found that reactions to overflights during spring were greater than at other times of the year and this response did not vary by sex.  Since male and female wild sheep are spatially segregated for much of the year, this final result is particularly interesting.  Bleich et al. (1994) suggest that bighorn sheep did not habituate to numerous helicopter overflights and they noted the potential for disturbance effects to be “exacerbated for animals living in heterogeneous environments, where critical resources are limited and widely distributed: mountain sheep are an excellent example of such a species”.

Physiological responses to aircraft overflights have also been investigated for bighorn sheep by examining heart rates. Weisenberger et al. (1996) documented an increase in heart rate for bighorn sheep exposed to simulated military jet aircraft overflights in a laboratory setting. During the summer, heart rate was higher during the overflight event and 3 minutes after the overflight than it was before the event.  In the spring, heart rate was only elevated during the overflight event.  Krausman et al. (1998), examined heart rates and behaviors in semi free-ranging bighorn sheep exposed to overflights of F-16 aircraft.  These authors found that heart rates could be more easily explained by animal activity than by the occurrence of an overflight event.  Behavior during this study was also not altered by overflights.  Both Weisenberger et al. (1996) and Krausman et al. (1998) conclude bighorn sheep habituate to overflight activity and suggest that bighorn sheep are unlikely to be adversely effected by military overflight.   

Data on the impacts of military aircraft on Dall’s sheep are nonexistent (Dept. of the Air Force 1995, Dept. of the Air Force 1992) and are mostly anecdotal for civilian fixed-wing aircraft (Anderson 1971, Linderman 1972, McCourt et al. 1974, Nichols 1972).  For Dall’s sheep, impacts of overflights are best documented for helicopters.  Lenarz (1974) in Canada documented reactions of 49 groups of Dall sheep to helicopters flown at horizontal distances of 300 –500 ft.  Thirty six percent of these sheep had a strong panic response, 49% had moderate reactions and 13% exhibited no reaction.  Lenarz (1974) observed ewes to be more reactive than rams.  Sheep in this study had been extensively overflown for 2 years prior to this study and the extent of reaction indicates no habituation was occurring for low-level helicopter overflights.  Dall’s sheep reactions to civilian aircraft in Atigun Gorge, Alaska varied considerably, with the most severe reactions occurring in response to helicopters (Anderson 1971).  Sheep in this study appeared to be more easily disturbed while at mineral licks.  Feist et al. (1974) noted that helicopters flown at altitudes of up to 1500 feet above ground level and horizontal distances of up to approximately 1 mile caused sheep to run. 

Most recently, Frid (1994, 1997, 2003) examined the impacts of helicopters on Dall sheep in southwest Yukon, Canada. Sheep were observed to leave an area when disturbed by helicopters and initiated responses to aircraft when the helicopter was 2.2 + 0.83 km (1.4 + 0.5 miles) distant (n=9).  During the summer of 1997, Frid (2003) found that the probability of a sheep reacting to an overflight was related to directness of approach of helicopters and the elevation of the approaching aircraft.  Factors that contributed to the probability and severity of a response included group size, number of lambs in the group, and distance to escape terrain.  Sheep would escape (move in response to the helicopter) farther if terrain features were such that a helicopter could surprise the animals by suddenly appearing or becoming audible.

STUDY SITE SELECTION

Two study sites were selected for examining the effect of military overflight events, Cope Thunder excercises and mitigated airspace on Dall’s sheep.  The first site, Cirque Lakes, is located in Yukon-Charley Rivers National Preserve and is overlain by mitigated airspace (Fig. 2).  The second site, West Point, is located approximately 35 km to the west of Cirque Lakes and has no associated mitigation measure.  Both sites occur within the boundaries of the interior Alaska Yukon 1 and 2 MOAs.  Study site selection was based on many criteria.  Both sites exhibit similar environmental characteristics. Sheep populations in both areas are disjunct, occur at low densities, and occupy atypical sheep habitat.  Topography in both areas is similar with a limited amount of rugged escape terrain occurring in relatively low, rounded mountains (Durtsche et al. 1990, Boudreau 1996).  History of disturbance from civilian aircraft, hunting pressure and recreation pressure is similar and minimal (Boudreau 1996).  Data are available for Dall sheep use in the Cirque Lakes area (Burch and Demma 1998, Burch and Lawler 2001) and in the West Point area (Durtshe et al. 1990).  This combined with the patchy distribution of Dall sheep habitat in interior Alaska allowed for delineation of study areas.  Observations by individuals familiar with the area indicate that West Point sees considerably more low-level military overflights than does Cirque Lakes, both in and out of the mitigated time period (Skip Ambrose, US Fish and Wildlife Service, pers. com.).

The final EIS (1995) projected mean daily military aircraft operations in the Yukon MOAs 1, 2, 3, and 4 to be 7 - 18 (Yukon MOA 4 and 1, respectively) aircraft operations per day in a routine flying day, and 164 - 206 (Yukon MOA 4 and 1, respectively) aircraft operations per day during MFE training. Supersonic activity in MOAs 1, 2, and 4 is authorized at or above 5,000 feet AGL or 12,000 MSL, whichever is higher (FAA Aeronautical Study 95-AAL-042NR).  Subsonic flight activity in Yukon MOAs 1, 2, and 4 can occur as low as 100 AGL (FAA Aeronautical Study 95-AAL-042NR).  Airspace in the Yukon 3 MOA is more complex.  The Yukon 3 MOA is split into 3 separate MOAs.  Yukon 3 High has a floor of 10,000 feet AGL and overlies the Yukon 3 Low MOAs.  Yukon 3A Low and 3B Low are divided by a line that runs from the northeast corner of this MOA to the intersection with the northeast corner of the Buffalo MOA.  Yukon 3A Low is the western portion of this MOA and has a floor 100 feet AGL. Yukon 3B Low, the eastern portion has a floor of 2000 feet AGL and is only used during MFEs.  Supersonic activity is authorized in the Yukon 3 High MOA but not in the Yukon 3A Low or 3B High MOAs (FAA Aeronautical Study 95-AAL-042NR). 

GOALS AND OBJECTIVES

This project was initiated to determine the effects of military overflights on Dall’s sheep and the effectiveness of the mitigation plan.  We addressed this goal by examining trends in population levels of Dall’s sheep in some areas under the interior Alaska MOA airspace.  We looked at Dall’s sheep productivity and survival rates in some interior Alaska MOAs areas.  Dall’s sheep behavioral reactions to military overflights were investigated as were Dall’s sheep daily movements, home range size, and habitat use. Dall’s sheep/military overflight relationships were investigated by comparing high intensity periods of military overflights (MFEs) with low intensity periods of military overflights (routine flying days), and by comparing areas with different overflight and mitigation histories.  Responses to specific overflight events were examined by comparing the proximity of an overflight and the sound level produced by the overflight.  Specific objectives are:

1) Identify areas of use by Dall’s sheep in Yukon MOAs 1 and 2 (areas where there is considerable low-level aircraft activity). 

2) Examine trends in Dall’s sheep populations in Yukon MOAs 1 and 2.

3)  Examine reproductive success, and survival of Dall’s sheep at 2 study sites within the MOA structure.  One study site is mitigated for low-level military overflights and the other is not. 

3)  Describe and compare Dall’s sheep relative activity, feeding efficiency and behavior in relation to Cope Thunders, mitigation measures, the frequency of overflight events, the proximity of the overflight event, and the sound level of overflight events.                          

4) Compare Dall’s sheep daily movements, home range size, and habitat use and characteristics in relation to Cope Thunders, mitigation measures, and frequency of military overflight events.

Byproducts of achieving the above objectives include an understanding of the timing of seasonal shifts in habitat use and life stages associated with these shifts in interior Alaska, and characteristics of Dall’s sheep habitat in interior Alaska. 

Project goals and objectives, as well as time, money, and personnel dictate which questions are most appropriate to pursue and the methods used to pursue them.  In this instance, we collected data on sheep movement, relative activity, and habitat use year round but focused behavioral and aspects of our study to those times of the year in which responses were expected to be the most evident.  Logically, this was immediately before and during Cope Thunders, when flying activity was the greatest.

Potential exists for differences in response to overflight activity based on sex of the animal.  Dall sheep are sexually segregated for much of the year.  Bleich et al. (1997) found that male and female mountain sheep select for different habitat variables.  Female sheep and their lambs occupied habitat with fewer predators and greater opportunities to avoid predation than did the larger body size, mature rams.  Rams selected areas with superior nutritional qualities and presumably, exposed themselves to greater predation risk. Differences in habitat choices and behavior between sexes have the potential to obscure differences in responses to military overflight activity.  Large sample sizes would be required to test for effects of disturbance on each sex of Dall sheep.  We eliminated this problem by limiting our study to ewes and their lambs.