Peninsular Bighorn Sheep Bring Magic to Palm Spring

The Bighorn Sheep is a large ungulate native to North America, found in mountain ranges from Southern Canada to Mexico.

Introduction

 

Hart Mountain National Wildlife Refuge hosted a population of 400+ bighorn sheep (Ovis canadensis) in the 1980’s, which would later sit at a stable ~150 individuals from 2009-2017.  Since this time, the population has faced a sharp decline to approximately 68 individuals, rendering the species more vulnerable to extirpation in the refuge than in over 40 years.  Isolating a single factor causing decline has proven difficult, so logically efforts should focus on the habitat needs of bighorn sheep.  Actions to address this decline must be taken in order to prevent further losses.

 

Comments

 

US Fish & Wildlife Services 

5275 Leesburg Pike, 

Falls Church, VA 22041-3803

 

Re:  Comments on Notice of Intent To Prepare a Bighorn Sheep Management Plan and Environmental Impact Statement - Comments Due 06/08/2020

 

Dear Danielle Fujii-Doe, 

 

Environmental Review has reviewed the proposed document and has the following comments:

 

  1. Regarding the Habitat Quality and Quantity section:  Changing plants communities can potentially translate into food shortages for herbivores.  Western juniper and cheatgrass have become significantly more common on the refuge, with the former having increased dramatically in the region.  According to Fryer & Termenstein, 2019, “In eastern Oregon, western juniper woodlands with >10% cover increased from 456,000 acres (184,500 ha) in 1936 to 2.2 million acres (890,000 ha) in 1988”.  The same source also claims that “The minimum time for the western juniper overstory to begin suppressing the shrub understory is 30 to 50 years”.  The refuge’s records state that the population of bighorn sheep during the late 1980’s was over 400 individuals.  40 years later the population is steadily declining.  Could it be that the refuge is currently feeling the effects of late-successional stage western juniper in a sagebrush steppe habitat?  Management actions should include population control of western juniper in order to improve overall habitat quality.

  2. Regarding the Habitat Quality and Quantity section:  Altered fire regimes go hand-in-hand with changing plant communities because fire plays a crucial role in regulating the introduction and coverage of species in ecosystems such as the sagebrush steppe.  According to Review and Update of the 1995 Federal Wildland Fire Management Policy, “By 1935, the U.S. Forest Service's fire management policy stipulated that all wildfires were to be suppressed by 10 am the morning after they were first spotted”.  This point in time coincides well with the start of western juniper’s expansion in eastern Oregon as mentioned in the previous comment.  By suppressing fires, the natural check against competitive species invading other communities has been removed.  How can species such as western juniper be safely managed in order to encourage species more palatable to bighorn sheep?  Prescribed burning must be used as a management action.  

  3. In reference to the section on Bighorn Sheep Survival and Mortality:  The refuge has recorded a near 50% drop in the population’s lamb to ewe ratio in the last three years.  In 2017, the ratio was 54.4 lambs to 100 ewes which would later fall to 21.5 and 22.7 lambs per 100 ewes in 2018 and 2019 respectively.  Habitat quality is essential to ensure lamb survival.  Lambs require a supportive habitat in order to be successful.  Smith et. al 1991 describes this as having ample escape terrain and lambing terrain, stating that “in some instances, inadequate quantities of lambing terrain have been cited as the ultimate factor controlling bighorn herd size (Hansen, 1982)”.  The article describes ideal lambing terrain as remote, rugged, and precipitous with nearby forage and a dry, southern exposure.  Has the lambing terrain on the refuge changed since the bighorn population’s decline, and if so, what treatments can be implemented in order to create more ideal lambing terrain?  Lambing terrain assessment must be considered to ensure that lamb recruitment rates will increase.   

  4. In reference to the section on Bighorn Sheep Survival and Mortality:  The reproductive capabilities and low density of this specific population must also be taken into account.  According to data provided by Hart Mountain National Refuge, of the remaining 68 sheep only 10 are males of reproductive age (rams).  This is a dangerously low number considering that at least 6 sheep on the refuge were killed by cougars since January of 2019.  Furthermore, Ruckstuhl, 1998 states that polygynous ungulate species such as bighorn sheep form social groups according to sex and spatially segregate for most of the year.  Would translocating disease-free rams from healthier bighorn populations be an effective means of increasing the amount of available breeding pairs for this population?  Translocating sheep from other populations is a fast way to ensure that reproductive rates rise and should be considered as part of the management plan.   

    Please direct all responses to these comments to the following email address: This email address is being protected from spambots. You need JavaScript enabled to view it.  

    Sincerely, 

      

    Matthew Coughlin - Associate in Maryland

     Environmental Reviewer 

     Environmental Review Inc.

     1792 Rogers Avenue

     San Jose, California  95112 

References

 

Department of the Interior. (2001). Review and Update of the

 

1995 Federal Wildland Fire Management Policy. Retrieved

 

from:  https://web.archive.org/web/20070810191055/http://www.nifc.gov/fire_policy/docs/chp1.pdf

 

Fryer, Janet L.; Tirmenstein, D. (2019). Juniperus occidentalis in Fire Effects Information System, Retrieved from 

 

https://www.fs.fed.us/database/feis/plants/tree/junocc/all.html

 

 

Ruckstuhl, K. E. (1998). Foraging Behaviour and Sexual Segregation in Bighorn Sheep. Animal Behaviour, 56(1), Retrieved from 

 

http://marco.recherche.usherbrooke.ca/pdffiles/Anim.Behav..pdf 

 

 

Smith, T. S., Flinders, J. T., & Winn, D. S. (1991). Habitat Evaluation Procedure for Rocky Mountain Bighorn Sheep in the Intermountain West. Great Basin Naturalist, 51(3) Retrieved from http://marco.recherche.usherbrooke.ca/pdffiles/Anim.Behav..pdf