Sign surveys for bighorn occupancy
Have you ever hiked in Death Valley or Joshua Tree National Park hoping to catch a glimpse of a desert bighorn ram looking down at you from atop a cliff? Did you succeed? Have you ever spotted a desert bighorn? We wouldn't be surprised if you answered no
Bighorn sheep are notoriously hard to find.
Sign, sign , everywhere some sign
Desert bighorn populations are typically small and spread out over several dozen difficult-to-access mountain ranges. They're also wary, blend in to their surroundings, and make use of rocky terrain to disappear in the blink of an eye. But what they're NOT good at is covering their tracks. Bighorn sheep leave behind all kinds of evidence of their presence, and we can more easily spot this "sign" and use it as a tool for monitoring certain bighorn sheep populations and habitats.
Compared to other survey methods, sign surveys can be useful for a number of reasons
- Low impact & appropriate for wilderness areas
- Low cost relative to helicopter fees & risks
- Feasible without prior information about bighorn activity or water resources
- Early indication that more costly surveys would be worthwhile
Our goal was to create a standard survey design so that bighorn sign surveys could be repeated across their range. If everyone uses the same approach and data format, it makes it easier to combine information and look at patterns over larger areas.
What does a bighorn sign survey look like?
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In this video, Paige Prentice (former CDFW bighorn biologist and current OSU graduate student) describes why sign surveys can be helpful to monitoring desert bighorn and OSU postdoc Christina Aiello gives you a run-down of what the survey looks like.
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Calibrating a new tool...
...and making improvements
Surveys in natural habitat don't always have consistent detection rates, so we're identifying conditions that improve bighorn sign detection so we can make our methods as efficient as possible.
Visuals from our sign survey calibration study & life in the field: We conducted surveys in 20 different mountain ranges known to have bighorn sheep populations in 2020 and 2021. The surveys spanned an enormous variety of terrain and conditions and the resulting data will help us determine what conditions result in the best detection rate.
THIS ANALYSIS IS IN PROGRESS. COME BACK TO SEE WHAT MAKES FOR AN EFFICIENT BIGHORN SIGN SURVEY
Current and future applications
We envision sign surveys as a tool for monitoring habitat with little data on bighorn sheep, where there may not be a stable population. Many mountain ranges used to support bighorn sheep, but their populations died out or left (went locally extinct). Through movement and dispersal, these empty habitats can be recolonized.
It's difficult to track these extinction & recolonization events, but knowing when and how often they occur gives us a better idea of how well the overall bighorn metapopulation is functioning. Sign surveys can help us monitor long-term trends in bighorn presence over large regions.
It's difficult to track these extinction & recolonization events, but knowing when and how often they occur gives us a better idea of how well the overall bighorn metapopulation is functioning. Sign surveys can help us monitor long-term trends in bighorn presence over large regions.
Even though our analysis is still underway, we could already tell that the survey worked pretty well. And we couldn't wait to try it out in habitat that was thought to still be unoccupied by bighorn. So off we went...
WONDERING WHAT ITS LIKE TO SEARCH FOR BIGHORN SIGN?
ONE MEMBER OF OUR FIELD TEAM SHARES HER EXPERIENCE IN A 2-PART BLOG
ONE MEMBER OF OUR FIELD TEAM SHARES HER EXPERIENCE IN A 2-PART BLOG