Using Passive Acoustic Monitoring to Estimate Bird Community Response to Land Management in Southeastern Georgia

Working lands, such as mine reclamation and timber production sites, may be able to provide supplementary habitat for declining disturbance-dependent birds, such as Bachman's Sparrow (Peucaea aestivalis) and Northern Bobwhite (Colinus virginianus). However, habitat use is likely contingent on specifics of land-use practices, especially those that could alter understory vegetation. My first research objective was to use autonomous recording units (ARUs) and BirdNET algorithms to compare the relative abundance of eight focal bird species across site treatments representing land management types: surface mine reclamation, timber production, young savanna, and mature savanna. All sites were established in upland pine (Pinus spp.) habitat throughout the southeastern Coastal Plain region of Georgia, USA from May-June 2024. I hypothesized that the mine reclamation site would support similar focal species, but in lower abundances than timber production and both savanna sites, and vegetation characteristics would also influence relative abundance along with site treatment. Model selection showed site treatment influenced relative abundance for all species and explained more variation in relative abundance than measured vegetation characteristics. The mine reclamation site had similar relative abundances for focal species when compared to the timber production site, suggesting these treatments provide comparable habitat. The young savanna site exhibited the highest abundances for most species, whereas the mature savanna site had lower abundances, suggesting some focal species may prefer habitat lacking overstories. Focal species responded differently to vegetation characteristics; for example, Common Nighthawk showed a positive response to grass cover, whereas Prairie Warbler responded negatively. My results provide strong evidence that site treatment influences the relative abundance of all focal species and highlight the need for future studies to parse out the exact mechanisms underlying these differences. Additionally, this study highlights the potential for working lands to provide habitat for disturbance-dependent birds and the effectiveness of using ARUs to assess the effects of land management on bird relative abundances. My second research objective assessed optimal survey frequency when using Royle-Nichols (RN) models to estimate abundance or relative abundance from ARU data. Passive acoustic monitoring with ARUs can enable efficient monitoring of avian populations. RN models may be well suited for estimating abundance or relative abundance from ARU detection/non-detection data; as repeated surveys can easily be conducted with ARUs. Yet, optimal survey effort using these methods remains unexplored. Using ARU data from four site treatments in southeastern Georgia, I assessed how survey frequency and mean cumulative detection probability influenced estimates for Blue Grosbeak (Passerina caerulea) and Bachman's Sparrow from May–June 2024. A baseline dataset of 50 daily surveys was subsampled into reduced frequencies: 25 surveys every 2nd day, 17 every 3rd day, 13 every 4th day, 8 every 7th day, and 5 every 10th day. RN models were fitted to each subsample. Abundance estimates decreased with subsampling, showing survey frequency arbitrarily influences estimates and RN models should be viewed as relative, not absolute, abundance estimates. However, the specific order of relative abundance across site treatments remained consistent for both species during subsampling, indicating RN models can still reliably infer effects across sites. Mean cumulative detection probability decreased with subsampling yet remained >70% for both species. Subsampling reduced precision in relative abundance estimates for both species; particularly for Bachman's Sparrow, emphasizing species-specific sensitivity to survey effort. However, subsampling every 2nd day or every 3rd day resulted in moderate losses of precision (≤ 34%) for both species, suggesting reduced survey frequency may be a viable strategy for efficient data collection depending on species detectability and study goals. Together, these findings from my research objectives highlight the potential of working lands to support disturbance-dependent bird conservation and demonstrate how passive acoustic monitoring with ARUs can be an effective tool for the conservation and management of bird populations.