Alligator River National Wildlife Refuge Research Articles

Identifying driving hydrogeomorphic factors of coastal wetland downgrading using random forest classification models

Coastal wetlands provide critical ecosystem services but are experiencing disruptions caused by inundation and saltwater intrusion under intensified climate change, sea-level rise, and anthropogenic activities. Recent studies have shown that these disturbances downgraded coastal wetlands mainly through affecting their hydrological processes. However, research on what is the most critical driver for wetland downgrading and how it affects coastal wetlands is still in its infancy. This study examined drivers of three types of wetland downgrading, including woody wetland loss, emergent herbaceous wetland loss, and woody wetlands converting to emergent herbaceous wetlands. By using random forest classification models for the wetland ecosystems in the Alligator River National Wildlife Refuge, North Carolina, USA, during 1995–2019, we determined the relative importance of different hydrogeomorphic processes and the dominant variables in driving the wetland downgrading. Results showed that random forest classification models were accurate (> 97 % overall accuracy) in classifying wetland downgrading. Multiple hydrogeomorphic variables collectively contributed to the coastal wetland downgrading. However, the dominant control factors varied across different types of wetland downgrading. Woody wetlands were most susceptible to saltwater intrusion and were likely to downgrade if the saltwater table was shallower than 0.2 m below the land surface. In contrast, emergent herbaceous wetlands were most vulnerable to inundation and drought. The favorable groundwater table for emergent herbaceous wetlands was between 0.34 m above the land surface and 0.32 m below the land surface, beyond which the emergent herbaceous wetland tended to disappear. For downgraded woody wetlands, their distance to canals/ditches played a crucial role in determining their fates after downgrading. The machine learning approach employed in this study provided critical knowledge about the thresholds of hydrogeomorphic variables for the downgrading of different types of coastal wetlands. Such information can help guide effective and targeted coastal wetland conservation, management, and restoration measures.

Detecting Coastal Wetland Degradation by Combining Remote Sensing and Hydrologic Modeling

Sea-level rise and climate change stresses pose increasing threats to coastal wetlands that are vital to wildlife habitats, carbon sequestration, water supply, and other ecosystem services with global significance. However, existing studies are limited in individual sites, and large-scale mapping of coastal wetland degradation patterns over a long period is rare. Our study developed a new framework to detect spatial and temporal patterns of coastal wetland degradation by analyzing fine-scale, long-term remotely sensed Normalized Difference Vegetation Index (NDVI) data. Then, this framework was tested to track the degradation of coastal wetlands at the Alligator River National Wildlife Refuge (ARNWR) in North Carolina, United States, during the period from 1995 to 2019. We identified six types of coastal wetland degradation in the study area. Most of the detected degradation was located within 2 km from the shoreline and occurred in the past five years. Further, we used a state-of-the-art coastal hydrologic model, PIHM-Wetland, to investigate key hydrologic processes/variables that control the coastal wetland degradation. The temporal and spatial distributions of simulated coastal flooding and saltwater intrusion confirmed the location and timing of wetland degradation detected by remote sensing. The combined method also quantified the possible critical thresholds of water tables for wetland degradation. The remote sensing–hydrologic model integrated scheme proposed in this study provides a new tool for detecting and understanding coastal wetland degradation mechanisms. Our study approach can also be extended to other coastal wetland regions to understand how climate change and sea-level rise impact wetland transformations.

Critters of the Carolinas: A team of researchers and community scientists use trail cameras to study wildlife

Photo 1. A female American black bear (Ursus americanus) and her three cubs walking along an access road in Alligator River National Wildlife Refuge in Dare County, North Carolina, USA. Photo captured on a trail camera used for surveying endangered red wolves. Photo credit: Wildlands Red Wolf Survey. Photo 2. A large American black bear (Ursus americanus) walking along a natural area in Hyde County, North Carolina, USA. Photograph taken by a trail camera set by a wildlife biologist for the North Carolina's Candid Critters camera trapping project. Photo credit: North Carolina's Candid Critters. Photo 3. A gray fox (Urocyon cinereoargenteus) inspecting a trail camera set by primary school students with the Museum of Life and Science in North Carolina, USA, for the Students Discover North Carolina camera trapping project. Photo credit: Students Discover North Carolina. Photo 4. A coyote (Canis latrans) inspecting a trail camera set by a community science volunteer in Dare County, North Carolina, USA. Trail camera set as part of the North Carolina's Candid Critters citizen science project. Photo credit: North Carolina's Candid Critters. Photo 5. A gobbler (male) wild turkey (Meleagris gallopavo) caught on a trail camera set by a community science volunteer in Needmore Game Land, found in the Blue Ridge Mountains of North Carolina, USA. Trail camera set as part of the North Carolina's Candid Critters citizen science project. Photo credit: North Carolina's Candid Critters. These photographs illustrate the article “Carolina Critters: a collection of camera trap data from wildlife surveys across North Carolina” by M Lasky, A Parsons, S Schuttler, B McShea, G Davis, L Kalies, R Sutherland, SR Clark, G Hess, H Boone, L Gatens, C Olfenbuttel, J Shaw, C Dukes, T Menke, J Matthews, and RW Kays published in Ecology. https://doi.org/10.1002/ecy.3372.

Self-reported and observed behaviors during black bear viewing at Alligator River National Wildlife Refuge

Social norms are commonly used to investigate visitor beliefs about acceptable wildlife encounters in parks and protected areas. However, there is little information detailing if self-reported norms match actual behaviors. This study compared self-reported norms (n = 304) for viewing distances of adult and cub black bears with behavioral observations (n = 355) of actual encounters at Alligator River National Wildlife Refuge, North Carolina, USA. First, we conducted a crossover design to examine the impact of viewing different groupings of bears at varying distances on acceptability beliefs. Our design significantly affected self-reported, minimum acceptable distance thresholds for an adult bear with cubs (Sequence 1 = 40.69 m; Sequence 2 = 48.24 m). Next, we found self-reported thresholds strongly differed from actual behaviors: 45 % of observations documented visitors closer than 40.69 m from bears. These findings illustrate the value of mixed-methods approaches to understand wildlife viewing behaviors and inform management actions.

Gut Microbiomes Differ Among Dietary Types and Stool Consistency in the Captive Red Wolf (Canis rufus).

Captive management of many wildlife species can be challenging, with individuals displaying health disorders that are not generally described in the wild population. Retrospective studies have identified gastrointestinal (GI) diseases, in particular inflammatory bowel disease (IBD), as the second leading cause of captive adult red wolf (Canis rufus) mortality. Recent molecular studies show that imbalanced gut microbial composition is tightly linked to IBD in the domestic dog. The goal of the present study was to address two main questions: (1) how do red wolf gut microbiomes differ between animals with loose stool consistency, indicative of GI issues, and those with normal stool consistency and (2) how does dietary type relate to stool consistency and red wolf gut microbiomes? Fresh fecal samples were collected from 48 captive wolves housed in eight facilities in the United States and from two wild wolves living in Alligator River National Wildlife Refuge, NC, United States. For each individual, the stool consistency was categorized as loose or normal using a standardized protocol and their diet was categorized as either wild, whole meat, a mix of whole meat and kibble or kibble. We characterized gut microbiome structure using 16S rRNA gene amplicon sequencing. We found that red wolves with a loose stool consistency differed in composition than wolves with normal stool consistency, suggesting a link between GI health and microbiome composition. Diet was not related to stool consistency but did significantly impact gut microbiome composition; gut microbiome composition of wolves fed a kibble diet were significantly different than the gut microbiome composition of wolves fed a mixed, whole meat and wild diet. Findings from this study increase the understanding of the interplay between diet and GI health in the red wolf, a critical piece of information needed to maintain a healthy red wolf population ex situ.

Carbon Chemistry of Intact Versus Chronically Drained Peatlands in the Southeastern USA

AbstractThe Great Dismal Swamp National Wildlife Refuge (GDS) is a large temperate swamp in Virginia/North Carolina, USA with peat soils historically resistant to microbial decomposition. However, this peatland has been subject to ~200 years of disturbance during which extensive drainage, fire suppression, and widespread logging have increased decomposition and dramatically decreased the distribution of Atlantic white cedar (AWC). The purpose of this study was to determine the impact of long‐term drainage and AWC loss on the carbon chemistry of GDS peats. Peat cores were collected from three drained GDS vegetation communities (pocosin, AWC, and red maple‐black gum) and compared to cores collected from an intact, undrained AWC peatland at the Alligator River National Wildlife Refuge (AR) in North Carolina. The AR peats had higher lignin content in the deeper peat intervals, and lignin content and percent organic carbon were largely invariant with depth compared to the GDS peats. The concentrations of syringyl group phenols were greater in the surface layers of GDS peats, likely reflecting the selective removal of AWC and transition from gymnosperms to angiosperms. Acid to aldehyde ratios for vanillyl and syringyl group phenols indicated that the GDS peats were more decomposed, particularly at depth, and that this occurred under aerobic conditions. Moreover, solid‐state 13C NMR confirmed a coincident loss of carbohydrates and increase in recalcitrant by‐products of carbohydrate degradation with depth. These data indicate that long‐term drainage has accelerated the decomposition of peat at the GDS, reducing the capacity and stability of the carbon sink.

Estimation and Uncertainty of Recent Carbon Accumulation and Vertical Accretion in Drained and Undrained Forested Peatlands of the Southeastern USA

AbstractThe purpose of this study was to determine how drainage impacts carbon densities and recent rates (past 50 years) of vertical accretion and carbon accumulation in southeastern forested peatlands. We compared these parameters in drained maple‐gum (MAPL), Atlantic white cedar (CDR), and pocosin (POC) communities in the Great Dismal Swamp National Wildlife Refuge (GDS) of Virginia/North Carolina and in an intact (undrained) CDR swamp in the Alligator River National Wildlife Refuge (AR) of North Carolina. Peat cores were analyzed for bulk density, percent organic carbon, and 137Cs and 210Pb. An uncertainty analysis of both 137Cs and 210Pb approaches was used to constrain error at least partially related to mobility of both radioisotopes. GDS peats had lower porosities (89.6% (SD = 1.71) versus 95.3% (0.18)) and higher carbon densities (0.082 (0.021) versus 0.037 (0.009) g C cm−3) than AR. Vertical accretion rates (0.10–0.56 cm yr−1) were used to estimate a time period of ~84–362 years for reestablishment of peat lost during the 2011 Lateral West fire at the GDS. Carbon accumulation rates ranged from 51 to 389 g C m−2 yr−1 for all sites. In the drained (GDS) versus intact (AR) CDR sites, carbon accumulation rates were similar with 137Cs (87GDS versus 92AR g C m−2 yr−1) and somewhat less at the GDS than AR as determined with 210Pb (111GDS versus 159AR g C m−2 yr−1). Heightened productivity and high polyphenol content of peat may be responsible for similar rates of carbon accumulation in both drained and intact CDR peatlands.

Effects of Filter Strips on Habitat Use and Home Range of Northern Bobwhites on Alligator River National Wildlife Refuge

Lack of breeding habitat for northern bobwhites (Colinus virginianus) on agricultural landscapes is a factor that limits populations. Therefore, we examined how the addition of filter strips around crop fields and along crop field drainage ditches impacted northern bobwhites. Our study focused on habitat use, home range and brood-rearing range of bobwhites, from April through September I 993-94. Two farms on Alligator River National Wildlife Refuge were sub-divided into filter strip (FS) and non-filter strip (NFS) sections. More bobwhites were found on FS sections than on NFS sections based on flush counts (4.3x more on FS areas: P = 0.02). We used log-linear analysis to examine the distribution of telemetry locations (n = 1796) of radio-marked bobwhites (n = 218) across 5, 4.6m bands parallel to drainage ditches. Bobwhite locations were skewed towards ditches, particularly on FS sections before soybeans matured to a size that was sufficient to provide canopy cover for bobwhites. Bobwhites captured on FS sections had significantly smaller breeding season ranges than those captured on NFS sections (P = 0.001). Adult and sub-adult breeding season (May-Aug) ranges (n = 23) averaged 32 ha (SE = 26) and 182 ha (SE = 41) on FS and NFS sections, respectively. Brood ranges to 14 days (n = 9) ranged from 0.8 ha to 2.2 ha depending on habitat and calculation method. Presence of filter strips shifted habitat use patterns, especially during spring and early summer, and improved crop fields as habitat for breeding bobwhites.

Measures of Space use and Association of Two Unrelated Male Red Wolves in a Shared Area

The United States Fish and Wildlife Service (USFWS) listed the red wolf (Canis rufus) as an endangered species in 1967 and began a recovery program in 1973 (USFWS 1989). By that time, however, the red wolf had already been extirpated from most of its range (McCarley and Carley 1979). Only 1 wild population of red wolves currently exists, reintroduced in 1987 to the Alligator River National Wildlife Refuge (ARNWR) in northeastern North Carolina, U.S.A. (USFWS 1989). Most research on the red wolf has addressed its status as a species (e.g., Wayne and Jenks 1991; Wilson et al. 2000; Kyle et al. 2006; Murray and Waits 2007). Ecological studies have been limited by small sample sizes or duration (Mauney 2005; Hinton 2006; Chadwick et al. 2010; Hinton and Chamberlain 2010) or by VHF telemetry data collection that is infrequent and limited to daytime observations (Phillips et al. 2003). Although GPS and VHF radio collars are used to monitor the population, intra-group spatial relationships are largely undocumented. Red wolves form groups consisting of the breeding pair and their sexually immature offspring (Phillips et al. 2003) and offspring from previous years have been observed as helpers at the den (Sparkman et al. 2010). Unrelated wolves of the same gender have not been previously reported in the same group. In this study, 2 unrelated male red wolves using a shared area were monitored 5 times per day for 12 months using GPS collars. The purpose was to determine if the non-breeding male was a member of the group composed of the breeding male and his mate, an uncollared female. We hypothesized that association between the males would be high if the non-breeder was a member of the group, whereas there would be no significant association if the nonbreeder was simply using the same area. If the unrelated non-breeder was a group member, this represents a unique pack composition that has not been studied in this species. Methods

An efficient method for screening faecal DNA genotypes and detecting new individuals and hybrids in the red wolf (Canis rufus) experimental population area

Previously, sequencing of mitochondrial DNA (mtDNA) from non-invasively collected faecal material (scat) has been used to help manage hybridization in the wild red wolf (Canis rufus) population. This method is limited by the maternal inheritance of mtDNA and the inability to obtain individual identification. Here, we optimize the use of nuclear DNA microsatellite markers on red wolf scat DNA to distinguish between individuals and detect hybrids. We develop a data filtering method in which scat genotypes are compared to known blood genotypes to reduce the number of PCR amplifications needed. We apply our data filtering method and the more conservative maximum likelihood ratio method (MLR) of Miller et al. (2002 Genetics 160:357–366) to a scat dataset previously screened for hybrids by sequencing of mtDNA. Using seven microsatellite loci, we obtained genotypes for 105 scats, which were matched to 17 individuals. The PCR amplification success rate was 50% and genotyping error rates ranged from 6.6% to 52.1% per locus. Our data filtering method produced comparable results to the MLR method, and decreased the time and cost of analysis by 25%. Analysis of this dataset using our data filtering method verified that no hybrid individuals were present in the Alligator River National Wildlife Refuge, North Carolina in 2000. Our results demonstrate that nuclear DNA microsatellite analysis of red wolf scats provides an efficient and accurate approach to screen for new individuals and hybrids.

Herpetofaunal Diversity of Alligator River National Wildlife Refuge, North Carolina

In the past century, habitat alteration and fragmentation have increased dramatically, which increases the need for improving our understanding of how species and biological communities react to these modifications. A national strategy on biological diversity has focused attention on how these habitat modifications affect species, especially herpetofauna (i.e., changes in species richness, community evenness and similarity, and dominant/rare species). As part of this strategy, we surveyed Alligator River National Wildlife Refuge, a coastal, mixed second-growth forested swamp (MFS) and pocosin wetland (PW), in North Carolina for amphibians and reptiles from September 2000 to August 2001. We randomly selected three sites (3 x 3 km) in two major habitat types (MFS, PW) and completed random surveys and trapping using transects, quadrats, nighttime aural road surveys, drift fences, canal transects, coverboards, incidental captures, and evening road surveys. We also col- lected herpetofauna opportunistically throughout the refuge to establish an updated species list. For analysis, we used Shannon-Weiner species diversity (H'), evenness (J'), species richness and species detectability (COMDYN4), and community percent similarity index to determine herpetofaunal community differences. We estimated 39 species in MFS and 32 species in PW (P < 0.10). Species detectability was similar between habitats (0.84 to 0.86). More reptilian species (+ 31%) inhabited MFS than PW, but estimated amphibian species richness was identical (17 spp.). H' was higher (P < 0.0001) for PW (2.6680) than for MFS (2.1535) because of lower J' in the latter (0.6214 vs. 0.8010). Dominance of three Rana species caused lower J' and H' in MFS. Similarity between the communities was 56.6%; we estimated 22-24 species in common for each habitat (95% CI = 18 to 31 spp.). We verified 49 of the 52 herpetofaunal species on the refuge that were known to exist in the area. Restoration of natural water flows may affect herpetofaunal diversity, which may be monitored during a restoration project. Currently, the refuge retains historical levels of herpetofaunal diversity for the region.

Potential impact of dare county landfills on Alligator River National Wildlife Refuge

Runoff of leachate from East Lake and Dare County Construction and Demolition Debris landfills has the potential to impact wildlife resources at Alligator River National Wildlife Refuge, Dare and Hyde Counties, North Carolina. Sediment quality of samples collected in August 2000 at 14 locations down-gradient from the landfills was assessed by measuring metal and organic contaminants in the sediments, chronic toxicity of solid-phase sediment (28-d static-renewal exposures; survival and growth as test endpoints) and acute toxicity of sediment porewater (96-h static exposures) to Hyalella azteca (Crustacea: Amphipoda). In addition, contaminant bioaccumulation from 4 sediments was determined using 28-d exposures of Lumbriculus variegatus (freshwater oligochaete). Although survival was not impaired, length of H. azteca was significantly reduced in sediments from 5 locations. Pore water from 4 locations was acutely toxic to H. azteca. Metals and a few polycyclic aromatic hydrocarbons (PAHs) were bioaccumulated by L. variegatus from the sediments. Several metals and PAHs exceeded sediment quality guidelines, and metals in porewater from several sites exceeded water quality criteria for the protection of aquatic wildlife. Runoff of leachate from the landfills has reduced sediment quality and has the potential to adversely affect wildlife resources at Alligator River National Wildlife Refuge.