Unique Threatened Species Benefits from Large-scale Grassland Conservation

AMERICAN BURYING BEETLE POPULATIONS INCREASE FOLLOWING COORDINATED, LARGE-SCALE RESTORATION ON PRIVATE RANGELANDS

What the American Burying Beetle lacks in charisma, it makes up for in conservation importance. Once found in 35 states and even into Canada, most remnant populations of the American Burying Beetle are now found in privately owned grasslands in the states of Nebraska, Kansas, Texas, Oklahoma, Arkansas, and South Dakota. The American Burying Beetle was first listed as endangered in 1989, but in 2020, its status was changed to threatened.

This large bug is known as a carrion beetle because it breeds and feeds in the carcasses of dead animals (mostly large rodents and birds), which it buries at night to hide from other scavengers. These nocturnal insects play an important role in ecology by helping recycle nutrients, and its presence or absence can help scientists and land managers gauge the overall health of the ecosystems where they live.

New Working Lands for Wildlife-affiliated research from Caleb Roberts, a U.S. Geological Survey research ecologist and Unit Leader at the Arkansas Cooperative Fish and Wildlife Research Unit, Department of Biological Sciences, University of Arkansas, showed that large-scale conservation actions in Nebraska’s Loess Canyons Experimental Landscape have increased the American Burying Beetle population.

Roberts and his team compared population counts from long-term studies conducted by the Nebraska Game and Parks Department to changes in land cover from 2007-2019. They found the population of American Burying Beetles increased by 17% in the Loess Canyons during the period studied.

The Loess Canyons provided an ideal location for this research. For decades, landowners, mostly cattle ranchers, have cooperatively managed encroaching eastern redcedar trees through prescribed fire and mechanical thinning. Their efforts have halted and even reversed tree encroachment throughout the Loess Canyons – one of the few examples of restoration success at an ecoregion scale. By defending and growing core grassland areas (large tracts of tree-free, undeveloped grasslands), landowners in the Loess Canyons helped set the stage for the first science-backed evidence of an ecoregion-scale population increase of the American Burying Beetle.

The researchers found that perennial grass cover was the only land cover variable that had a strictly positive relationship to American Burying Beetle abundance. They predicted that beetle populations would double when perennial grass cover reached between 46% and 80%. Conversely, beetle populations declined sharply when rangelands were converted to crop agriculture and when tree cover increased. At just 8-10% tree cover, American Burying Beetle abundance approached zero across a nearly 3,000-acres range.

The authors drew three major conclusions from their research.

First, maintaining intact, highly connected grasslands is the most effective way to conserve species like the American Burying Beetle. While beetle abundance declined only slightly when tree cover was low, maintaining low tree cover in grasslands is costly, inefficient, and difficult. This research shows that defending core grassland areas from invading trees, rather than trying to maintain a low amount of tree cover in grasslands susceptible to encroachment, will do the most good and the least harm for the American Burying Beetle.

Second, they note that their results support the expectation that conservation strategies that are spatially explicit and conducted at the functional scale of the target species will have the best chance of conservation success. In the Loess Canyons, the researchers found the highest abundance of beetles in the south-central portion of the region, where large-scale restoration activities (primarily prescribed fire) have increased perennial grassland cover and reduced eastern redcedar trees and where cropland conversion has had minimal impacts. Given that these large, core grassland areas have the highest abundance of beetles, the authors note that conserving intact grassland cores where the risk of cropland conversion is low has provided better conservation outcomes for beetles than trying to restore severely tree-infested areas or areas where rangelands are regularly plowed up.

Third, scale is important to even relatively small creatures like the American Burying Beetle. Beetle abundance declined significantly when just 0.1% of rangeland was converted in a 1,400-acre area. When tree cover increased to 8-10% in a 2,800-acre area, abundance declined to near zero. These findings further support large-scale grassland conservation – without an area large enough to support their complicated life history – beetle abundance fell sharply.

This research aligns with WLFW’s efforts in the Great Plains. WLFW’s Framework for Conservation Action in the Great Plains Grassland Biome identifies tree encroachment and land-use conversion as the two biggest threats facing the biome. Defending core grassland areas through proactive conservation that works across land ownership boundaries is embedded in this approach to grassland conservation, benefiting all who rely on these landscapes from ranchers and private landowners to rural communities to critters like the American Burying Beetle.

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POPULATION INCREASES OF THE THREATENED AMERICAN BURYING BEETLE (NICROPHORUS AMERICANUS) LINKED TO LARGE-SCALE CONSERVATION STRATEGIES IN A PRIVATE LANDS ECOREGION

Abstract: Woody plant encroachment and row-crop agricultural land conversion are existential threats to species that rely on grassland ecosystems. The American Burying Beetle (Nicrophorus americanus) is a threatened species whose largest remnant populations are predominantly located in grassland ecoregions comprised of privately-owned ranching lands.

Here, we seek to determine functional scaling patterns and population trends of the American Burying Beetle in the face of conservation threats and grassland restoration. We used 13 years (2007–2019) of American Burying Beetle abundance data collected from permanent sampling locations across the Loess Canyons ecoregion (Nebraska, USA), where a network of ranchers have been restoring large-scale grasslands. To estimate beetle abundance relative to land cover variables, we developed a Bayesian N-mixture model, incorporating the Bayesian latent indicator scale selection (BLISS) method to probabilistically determine at which scales land cover variables best explained beetle abundance. American Burying Beetle abundance exhibited high interannual variation but overall significantly increased across the ecoregion. Increases in beetle abundance were associated with large-scale (1149 ha extent) grassland cover. Decreases in abundance were associated with large-scale crop conversion (590 ha extent) and large-scale increases in woody cover (1149 ha extent).

This study provides the first evidence of ecoregion-scale population increases of the American Burying Beetle. These increases are tied to landscape variables that are managed in a large-scale, coordinated private lands grassland restoration effort. Our results suggest that successful grassland restoration will depend on coordinating across property boundaries to implement conservation at scales necessary to conserve species that require large-scale, unfragmented grasslands.

Citation: Caleb P. Roberts, Alison K. Ludwig, Dillon T. Fogarty, Erica F. Stuber, Daniel R. Uden, Thomas L. Walker, Dirac Twidwell, “Population increases of the threatened American burying beetle (Nicrophorus americanus) linked to large-scale collaborations in a working lands ecoregion,” Biological Conservation, Volume 301, 2025.

Permanent URL: https://doi.org/10.1016/j.biocon.2024.110865

Acknowledgements: Funding for this research was provided by Nebraska Game & Parks Commission [grant W-125-R-1], the University of Nebraska’s Institute of Agriculture and Natural Resources, the Arthur W. Sampson Fellowship Fund (University of Nebraska−Lincoln), the National Science Foundation’s National Research Traineeship program, and the Arkansas Game and Fish Commission through cooperative agreement 1434-04HQRU1567. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.