Response of red‐cockaded woodpeckers to military training operations
Authors: Delaney David K. , Pater Larry L. , Carlile Lawrence D. , Spadgenske Eric W. , Beaty Timothy A. , Melton Robert H. 
Published: July 2011

Military lands are a valuable resource in recovery of threatened, endangered, and at‐risk species worldwide and have the highest density of threatened and endangered species of all major land management agencies in the United States. Many red‐cockaded woodpeckers (Picoides borealis) that reside on federal lands occur on 15 military installations in the southeastern United States. This close association has increased concern over potential conflicts between conservation requirements of endangered species and the military's mission of combat readiness. Our objectives were to 1) determine if military training operations affect behavior, reproductive success, and productivity of red‐cockaded woodpeckers; 2) develop a frequency‐weighting function to assess woodpecker hearing sensitivity; 3) identify factors that affect woodpecker responses to military training operations; 4) develop distance and dose‐response thresholds for quantifying woodpecker responses to noise levels and stimulus distances; 5) characterize military training operations through quantification of sound levels, source identification, distance from active woodpecker nests, frequency spectra, duration, and frequency of occurrence; and 6) document baseline woodpecker nesting behavior. We conducted our study on the Fort Stewart Military Installation located in southeast Georgia, USA.

Downy woodpeckers, as surrogates for red‐cockaded woodpeckers, had their best hearing sensitivity within the peak range of the power spectrum of both downy and red‐cockaded woodpecker vocalizations, which is at a higher frequency than that of a typical passerine. Overall, woodpeckers had a reduced auditory sensitivity relative to human hearing sensitivity and other species of small birds, especially in the frequency range >4 kHz. Woodpeckers were most sensitive in the 1.5‐ to 4.0‐kHz range. Sensitivity appeared to drop off quickly at frequencies <1.0 kHz and >4.0 kHz. Overall, we did not find that the woodpecker‐frequency‐weighting function we developed provided a better predictor of woodpecker flush response compared with A‐weighting. More research is needed to better understand the relationship between frequency‐weighting functions and woodpecker response behavior.

Potential breeding groups of woodpeckers across the population increased from 158 in 1997 to 181 in 2000, wheras nesting groups increased from 141 in 1998 to 170 in 2000, for overall increases of 14.6% and 20.6%, respectively, over the 3 years of this project. Fledging success rates for individual nests within the overall population remained consistent from 1998 to 2000, averaging 84.4%. Mean clutch sizes for woodpecker groups for 1998 to 2000 ranged from 2.75 to 3.01 eggs/nest, brood size ranged from 2.01 to 2.22 nestlings/nest, whereas the average number of young fledged ranged from 1.57 to 1.76 young/occupied nest. We observed no difference in reproductive success or productivity between experimental and control‐tested red‐cockaded woodpecker groups. Overall, experimental test groups produced an average of 2.98 eggs/nest, 1.89 nestlings/nest, and 1.54 young/occupied nest from 1999 to 2000, compared with 2.73 eggs/nest, 1.91 nestlings/nest, and 1.57 young/occupied nest at control groups.

We measured behavioral responses (nest attendance and arrivals and departures from the nest) of red‐cockaded woodpeckers to military training events through direct and indirect (i.e., video surveillance) observation of 464.5 hours of woodpecker nesting behavior before and after controlled experimental events while recording and characterizing military‐generated sound events using sound‐recording equipment. We presented woodpeckers with actual 0.50‐caliber blank machine gun fire and artillery simulators from controlled distances to develop distance and sound thresholds. We used video surveillance to document potential behavioral responses of woodpeckers primarily during nonexperimental military training operations in areas that could not be safely monitored and to determine baseline woodpecker nesting behaviors. We recorded 2,846 nonexperimental military noise events in 157 data sessions at 50 red‐cockaded woodpecker groups from 1998 to 2000. We also recorded 206 experimental tests at 58 woodpecker groups during 1999 and 2000.

Life‐table analyses of flush response time showed that at short ranges (15–30 m) the flush response was stronger for artillery simulator blasts than for blank fire in both the incubation and the nestling phases. In contrast, at medium distances (45–60 m) blank fire tended to produce more flush responses than artillery fire in both incubation and nestling phases. At longer distances (>60 m), blank fire and artillery produced similar flush responses in the incubation phase, whereas flush response was stronger for blank fire than for artillery in the nestling phase. In general, most animals that responded to military activity flushed within 5 seconds of the stimulus event. Woodpeckers returned to nests within an average of 4.4 minutes after being flushed by artillery simulators and 6.3 minutes after 0.50‐caliber blank‐fire tests. Woodpecker flush response rates increased as stimulus distance decreased and sound levels increased, regardless of stimulus type or year. Woodpeckers did not flush from nests when 0.50‐caliber blank machine gun fire and artillery simulators were >152 m away and sound‐exposure levels (decibels [dB]) were <68 dBW (woodpecker‐based frequency‐weighting curve) and <65 dBW, respectively.

We found that blast treatments reduced arrival rates of adults at the nest, with the amount of reduction dependent on the type of blast stimulus and number of helpers at the nest. On the other hand, blast treatments had no detectable effects on nest attendance. The effect of blank fire on incubation‐phase arrivals over a 30‐minute interval (about 40% reduction) was nearly twice that of artillery simulator fire (about a 20% reduction). There was no evidence supporting any effect of stimulus type on arrivals during the nestling phase. Blast stimuli during incubation reduced arrivals by 40% when no helpers were present, but the strength of this effect decreased to 28% when one helper was present, and was only 6% for nests with ≥2 helpers. Distance of the blast from the nest did not affect the response of arrival rates to blast treatments.

Infrequent, short‐duration military training exercises, as measured, did not appear to substantially impact red‐cockaded woodpecker reproductive success and productivity on the Fort Stewart Military Installation. Our results may be applicable to other military installations where similar training activities and intensity levels occur. Additional research is needed to address possible habituation or sensitization of red‐cockaded woodpeckers to human activities in proximity to active nest sites. Although we attempted to monitor woodpecker response to a number of military training activities, other types of military training operations or human‐based activities with louder noise, longer duration, increased human presence, and greater frequency of occurrence could more negatively influence woodpecker nesting behavior and need to be investigated. Our results do not support the hypothesis that military maneuver training operations are limiting factors in the recovery of red‐cockaded woodpeckers on military installations, based on our level and type of testing. Natural resource management policies on military installations have had a positive influence on the recovery of red‐cockaded woodpeckers and probably outweigh the negative effects of typical military training. © The Wildlife Society, 2011