The New Mexico Rare Arthropod Resource

This species is found in rocky alpine areas, namely rockslides and rocky ridges near grassy areas (Scott 1986, Glassberg 2001, Cary and Toliver 2024, Montana Natural Heritage Program 2024). In the southernmost part of the range, this butterfly exists above the tree line. It occurs up to 3,505 m (11,500 ft) in New Mexico and up to 4,200 m (13,780 feet) in Colorado (Brown 1957, Scott and Scott 1978, Cary and Toliver 2024, Montana Natural Heritage Program 2024).

As larvae, the diet is thought to consist of alpine grasses, such as Sedges (Carex spp.), Festuca, Rushes (Juncus spp.), Woodrushes (Luzula spp.), and Meadow-Grasses (Poa spp.) (Scott 1986, 1992, 2006; Montana Natural Heritage Program 2024). As adults, they are known to nectar on Alpine Forget-Me-Nots (Myosotis alpestris), Phlox, Dryas, Fleabane (Erigeron), Haplopappus spp., and Catchflies (Silene spp.) flowers (Opler and Wright 1999, Glassberg 2001, Scott 2014, Montana Natural Heritage Program 2024).

The subspecies flies from late June to August with just one flight. New Mexico records stretch from July 2 to July 24 (Scott 1986, Opler and Wright 1999, Cary and Toliver 2024). During flight males spend all day patrolling for females above depressions and over rockslides (Scott 1986). The host plant is unknown but females lay eggs on rocks near Rushes (Juncaceae), Grasses (Gramineae), and Sedges (Cyperaceae)(Scott 1986). There are also records of females laying eggs directly on Sedges (Carex spp.) (Scott and Scott 1978; Scott 1986, 1992, 2006; Guppy and Shepard 2001; Montana Natural Heritage Program 2024). The larvae are thought to be biennial hibernators, overwintering their first winter as L2 or L3 instars (Scott and Scott 1978; Scott 1986, 1992, 2006; Opler and Wright 1999; Guppy and Shepard 2001; Montana Natural Heritage Program 2024).

The Southern Rockies Magdalena Alpine is the southern Rocky Mountains subspecies of the Magdalena Alpine (Erebia magdalena). It occurs in the mountains of Colorado, southern Montana, northern New Mexico, northeastern Utah, and western Wyoming (Lotts and Naberhaus 2023, Cary and Toliver 2024, Pelham 2024). In Montana this butterfly has historically been reported in Carbon County and was reported in Park County in 2011 (Montana National Heritage 2024). It is found in isolated populations, living exclusively on top of mountain peaks. At the southern extreme of its range in New Mexico, this butterfly has been reported on Wheeler Peak and State Line Peak (Cary and Toliver 2024). In the last 20 years, the butterfly has only been recorded in five mountain ranges, including Montana’s Beartooth Mountains, the southern portion of Wyoming’s Wind River range, Utah’s Uinta Mountains, the north central portion of the Colorado Rockies, and in Colorado/New Mexico’s Sangre de Cristo Mountains (GBIF.org 2024).

There are conservations actions in place for this butterfly. The subspecies is currently being considered for inclusion as a Species of Greatest Conservation Need in the New Mexico State Wildlife Action Plan 2025 revision, based on its adversity to climate change, low population numbers, and limited range (New Mexico Department of Game and Fish 2024). Additional, research is needed on the distribution, population size and trend, habitats and ecology, and threats. In particular, determination of host plant would aid greatly in our understanding of this species and its conservation needs.

This butterfly is a cold-adapted Pleistocene ice age relict, now only residing on high mountain peaks (Scott 1986, Cary and Toliver 2024). The Western United States is becoming increasingly hot and dry as the climate warms (Cook et al. 2009, Cook et al. 2015, Williams et al. 2022) and warming trends are predicted to be more pronounced at higher elevations (Mountain Research Initiative EDW Working Group 2015). Many organisms, including butterflies, respond to climate change by shifting to higher elevations or latitudes (Forister et al. 2010, Holland 2010, Rödder et al. 2021). If this subspecies responds to climate warming in this way, it would soon run out of habitat to shift into, as it already occurs near the top of mountains.

Inbreeding depression may also be a major threat to this butterfly as populations are small and isolated. Inbreeding depression results when slightly deleterious alleles accumulate in a small population, reducing the likelihood of population persistence (Hedrick 1994, Lynch et al. 1995). The accumulation of deleterious alleles and reduction in heterozygosity have been shown to reduce survival rates at several important life stages in butterflies, including those that have an effect on population stability and persistence, even after just one generation of mating between full-siblings (Saccheri et al. 1998, Nieminen et al. 2001).

This species is biennial, and therefore takes two years to develop. Spending two years as larvae with limited mobility, leaves butterflies more vulnerable to environmental stochastic events such as extreme weather, wildfires, and predation (Scott 1986, Montana Natural Heritage Program 2024).

As a result of its biennial life history and because its range has experienced drastic changes in climate in the last three decades, the parent species of this butterfly has been identified as one of the most imperiled butterflies in the western United States (Forister et al. 2023).

The population size and trend are not known for this subspecies. It is rarely recorded and is reportedly quite rare (Glassberg 2001, Montana Natural Heritage Program 2024). In the last 10 years, there have been just 30 recorded observations (GBIF.org 2024), though one must high to high altitudes to find the species. Determination of population size and monitoring of population trends is necessary to ensure the population is stable, especially as several widespread, relatively common species of butterfly are in decline across the western United States (Forister et al. 2021).

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