 to land use changes, including redcedar expansion, and the New England populations and Missouri reintroduction could be lost if active management and habitat protection are not continued. The combined effects of land use and future changes in climate are likely to impact the resiliency of most populations and the overall viability of the species.
Recent development and potential expansion of wind energy projects could also add to impacts from other land use changes. Potential land use impacts related to an expanding wind industry in the Northern Plains were not fully evaluated in the SSA Report (Service 2019) due to limited information, so additional analysis is recommended to improve the reliability of land use projections. The construction of wind turbines, roads, and powerlines has direct permanent habitat impacts and fragments the remaining habitat. The operation of wind turbines also has potential for direct take through American burying beetle collisions with the blades. However, future land use effects related to wind power were not factored into land use scenarios because we did not have estimates of future development or total areas that may be affected by wind projects, and no studies have evaluated the effects of wind projects on American burying beetles. The most significant threat to the American burying beetle is changes in climate. This threat affects the southern populations more than those in northern locations due to the southern population areas already experiencing temperatures near the species critical thermal tolerances. Therefore, changes in climate within the foreseeable future is an existential risk only to those populations in the southern portion of the species range. Here we present a summary of climate-related risks; additional information is available in the SSA Report (Service 2019). The SSA Report's chapter 3 summarizes general climate risks, chapter 4 includes current risks, and chapter 5 covers future risks (Service 2019).
Most considerations of climate change in Endangered Species Act classification decisions hinge upon whether climate change will manifest in changing habitat conditions and how the species is likely to respond to these changes in the future. Therefore, a key consideration for classification decisions where climate change is a potential stressor is how we interpret “foreseeable future” in the definition of a threatened species under the Act.
We use projections from two RCPs (4.5 and 8.5) to account for uncertainty regarding future atmospheric greenhouse gas concentrations. RCP 4.5 is at the low end of the intermediate range of conditions projected while RCP 8.5 is the high end of IPCC projections of atmospheric conditions. By using both a very high and low emissions scenarios in our projections, we bracketed the likely possibilities for climate change in the future. For ease of reference, we refer to these as “emissions scenarios,” although they are not based solely on emissions of greenhouse gases.
Our approach of using the two RCPs is consistent with the current widespread scientific practice of considering projections based on RCP 4.5 and RCP 8.5 so as to consider a range of projected conditions, rather than relying on a single scenario. The U.S. Global Change Research Program used these two RCPs as the core scenarios for the Fourth National Climate Assessment (Hayhoe et al. 2017), and they also are used as the basis for projections generated via the U.S. Geological Survey's National Climate Change Viewer. Although it is theoretically possible to achieve the RCP 2.6 pathway and outcome, we did not use it as it is not feasible or likely; numerous scientific papers show that key assumptions underlying it already have not been met (including a very rapid reduction in greenhouse gas emissions) and other future activities it relies upon are highly speculative. RCP 4.5 and 8.5 scenarios are more feasible and widely used for future climate assessments. Further, we did not use RCP 6 because the specific datasets used in our analyses are only available for RCP 4.5 and 8.5.
The life-history characteristics of American burying beetles indicate limited ability to tolerate warmer temperatures. Adult American burying beetles use secretions to slow decomposition of carcasses they bury for reproduction (see Summary of Species Requirements, above, for more information on the role of carcasses in reproduction). The carcasses are buried and must support both adults and larvae for at least 2 to 3 weeks, but high temperatures reduce the effectiveness of the secretions and accelerate decomposition (Jacques et al. 2009, p. 871). While the American burying beetle has life-history requirements similar to other carrion beetles, it is the largest Nicrophorus in North America and requires a larger carcass to reach its maximum reproductive potential (i.e., to raise a maximum number of offspring) than the other burying beetles (Service 1991, p. 2; Kozol et al. 1988, p. 37; Trumbo 1992, pp. 294-295). American burying beetles also have a longer time period for egg and larval development than other Nicrophorus carrion beetles, so the carcass must last longer (at least 12 to 14 days) to provide food and moisture for adults and support development of their larvae to the pupa stage. Temperature-related increases in decomposition and development of fly larvae would limit or prohibit reproductive success for American burying beetles if carcasses are in a suitable condition for shorter periods of time or do not last long enough to support development of their larvae.
The distribution of American burying beetles and other burying beetles in the Nicrophorus genus also indicates a limited ability to tolerate warmer temperatures. Nicrophorus abundance and diversity are higher in cooler climates. There are 15 Nicrophorus species in the United States and Canada, but only 2 are endemic to Central and South America, and they occur at higher elevations with cooler temperatures. Reasons for burying beetles' lack of success in warmer climates include increased competition with flies and ants (Peck and Anderson 1985 p. 248, Jiron and Cartin 1981 entire, Trumbo 1990 p. 6-7), as well as increased rates of carcass decomposition (Jacques et al. 2009. p. 871). Carcass decomposition is dominated by dipteran species (true flies), and the diversity of dipteran species using carcasses increases in warmer climates. Based on species distributions and existing climate conditions, few Nicrophorus species appear to be capable of maintaining populations in areas with long-term average summer mean-maximum temperatures at or exceeding a 95 °F threshold (N. carolinus, and possibly N. pustulatus and N. marginatus), and there are no Nicrophorus species in areas with average summer mean-maximum temperatures exceeding 100 °F.
Under both RCP 4.5 and 8.5 emissions scenarios, all American burying beetle populations in the Southern Plains Analysis Areas would be projected to have summer mean-maximum temperatures exceeding 95 °F within the mid-century time period. Surveys for American burying beetles in locations that have experienced a mean-maximum temperature near or above 95 °F during summer have shown declining capture rates the following year. Existing survey information from Fort Chaffee (Arkansas River Analysis Area) from 1992 through 2016 supports our conclusion that mean-maximum temperatures above 95 °F would adversely affect American burying beetle populations. During the study, catch rates of American burying beetles declined from the previous year every time mean-maximum temperatures exceeded 95 °F, which happened a total of six times throughout the study period. Based on this information, we anticipate continued population declines and potential extirpation if mean-maximum temperatures exceeding 95 °F became the average during summer months and more extreme temperatures occur more frequently.
Southern populations of American burying beetles that experience summer mean-maximum temperatures near 95 °F are declining. Since 2008, only seven American burying beetles have been detected within the Oklahoma portion of the southernmost analysis area, and no American burying beetles have been documented in the Texas or Arkansas portions. We have no evidence to suggest that habitat conditions that might otherwise explain the observed declines within these areas have significantly changed. American burying beetles were last detected in Texas in 2008 and populations have declined or are extirpated in large protected areas like Camp Maxey, Texas, with no apparent changes in land use. It appears that temperatures near this area are at, or past, a threshold that would support American burying beetles. This conclusion may be further supported by the fact that the species does not exist south of the Red River area in Texas and Louisiana, where habitat, soil conditions, and carrion availability are likely to be similar. Thus, we conclude that the southern edge of the species' range is driven by the 95 °F temperature threshold.
Temperature has always limited the American burying beetle's range to some degree. Populations at the northern edge of the range are limited by cool nighttime temperatures and shorter growing seasons, whereas populations at the southern edge of the range are likely limited by high temperatures. The western edge of the species' range has been limited by reduced precipitation and soil moisture. Although temperature and other effects of climate change are expected to affect American burying beetles in both the northern and the southern parts of the range, we expect that the populations in southern areas will be affected sooner and to a greater extent based on projected temperatures. Under both the RCP 4.5 and 8.5 emissions scenarios, a majority of the Southern Plains analysis areas are expected to be near or exceed summer mean-maximum threshold temperatures (95 °F) by 2039, with potential to Start Printed Page 65249extirpate American burying beetles from most or all Southern Plains populations. Within the mid-century time period, all Southern Plains analysis areas are expected to exceed threshold temperatures under both the RCP 4.5 and 8.5 emissions scenarios, likely resulting in extirpation of the American burying beetle from these areas. American burying beetles near the southern and western