Abstract
Anthropogenic noise has recently gained attention in the scientific community as an important source of disturbance on wildlife populations. Anthropogenic noise can disturb animals in various ways, such as causing hearing loss, inhibiting female mate choice, and altering the breeding behavior of displaying males. The effects of anthropogenic noise vary among species and likely differs based on the type and context of the noise. Anthropogenic noise is a pervasive disturbance that alters the distribution and reproductive success of many species and could help explain some wildlife population declines.Greater sage-grouse (Centrocercus urophasianus) are a disturbance-sensitive species experiencing range-wide abundance declines. The lek mating system and high lek fidelity of adult males make sage-grouse particularly sensitive to noise disturbance. Sage-grouse avoid attending leks with greater chronic noise disturbance, yet the effects of chronic noise may not be the same as the effects of loud, intermittent noise, and we have little information regarding the effects of loud, intermittent noise on sage-grouse. Sage-grouse experience a novel source of noise disturbance in portions of their range: intermittent, high intensity noise from low-level flyovers by military aircraft. Mountain Home Air Force Base conducts broad-scale aviation military training and combat simulations within sage-grouse breeding habitat in training areas throughout the sagebrush steppe of southwestern Idaho, northern Nevada, and southeastern. The primary objective of this study was to document the effect of intermittent noise from military overflights on lek attendance, lekking behavior, and nesting success of greater sage-grouse.
In Chapter 1 we used general linear models to estimate the influence of noise on the lek attendance and behavior of male greater sage-grouse. We placed audio equipment and video recording devices on lek perimeters to record attendance and document lekking male sage-grouse behavior. Our results demonstrate that increasing levels of Leq and Lmax during daytime hours contributed to lek attendance declines during the first two-thirds of the lekking season; the negative association between noise and attendance lessened after 7 April. We also used a scan-sampling approach to document the time budget of lekking male sage-grouse and determine how males’ behavior was influenced by noise disturbance from low-level military flyover. None of our measured noise levels influenced behaviors on an hourly scale or a yearly scale, but behavior was significantly influenced on a daily scale. We observed a slight increase in display rate from the beginning of the season until the last week of March and a significant decrease in displays after the first week of April. On-lek movement and inactivity increased as the season progressed. Alertness was highest early in the lekking season coinciding with the time male attendance was most sensitive to anthropogenic noise disturbance, and alertness probability sharply decreased through 1 April.
In Chapter 2 we used a logistic exposure model to estimate daily nest survival, the factors that influence daily nest survival, and the odds of nest survival based on the influence of our explanatory variables. We radio-marked sage-grouse hens and placed audio monitoring equipment near nests to determine if noise exposure from military activity influenced nest fate. Nests in 2022 had more instances of loud noise and lower nest success than 2023, but the within-year difference was not reflected in the top selected model. L10 was higher during nest-check intervals when nests failed compared to intervals when nests survived, but Lmax was lower during nest-check intervals when nests failed compared to intervals when nests survived. Lmax was lower for failed nests in each of the 2 years, but higher for failed nests when combining both years of data. We detected a relationship between loud noise events and a decreased probability that a nest survives the immediate 2-4 day interval or the following 2-4 day interval, and we detected a relationship at the scale of the entire nesting attempt; a nest frequently exposed to loud noise events was more likely to fail than a nests exposed to fewer loud noise events.
Greater sage-grouse respond to intermittent noise disturbance similarly to chronic noise disturbance. To our knowledge, this is the first study to explicitly measure the sound levels at greater sage-grouse nests exposed to noise disturbance from military low-level flyovers. Species-specific responses to loud, intermittent noise events and differential responses based on the noise source emphasize the importance of targeted research on the effects of anthropogenic noise, especially regarding species of management concern. Additional research on the effects of noise on sage-grouse behavior and reproduction metrics will help management agencies set appropriate policies, and additional studies are warranted because previous studies have documented that some declines in sage-grouse lek attendance are attributed to anthropogenic noise disturbance.