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As part of a four year ongoing study, the Arizona Game and Fish Department (AZGFD) is continuing to monitor the Santa Catalina sheep population. AZGFD released an additional 29 desert bighorn sheep in November 2015, bringing the total number of bighorns released in the Santa Catalina Mountain range to 90 since 2013. Nearly all of these sheep have been outfitted with GPS collars for monitoring.
Twenty-three lambs have been counted so far this season, including the first of a generation truly native to the Santa Catalinas. Biologists estimate as many as 85 sheep now live on the mountain. A helicopter survey this fall will give a better estimate of population numbers and recruitment success.
The project has been effective at determining cause specific mortality, but is still seeking to better understand the relationship between bighorn sheep and mountain lions. Factors such as topography, vegetation type, and group size may increase the risk of predation. Continuing to observe the growing herd, its composition and preferred habitat, will provide valuable management information.
Researchers have seen that mountain lions are the primary source of mortality for the bighorn population. Since the initiation of an Adaptive Mountain Lion Management Plan, five lions have been removed from the ecosystem. This plan has been extended until November 2017 by the AZGFD to ensure the sheep population reaches a sustainable level.
Understanding habitat selection, how it has changed since the reintroduction, and how it relates to predator avoidance is key to this study. Researchers will address several questions, including why some sheep populations are threatened by mountains lions while others can sustain high predation rates. Is there an optimal size in which the population can sustain natural predation? Can management actions, such as lion removal, be discontinued after that population size is reached? Data on recruitment rates, survival rates, mortality factors and age-specific survival will inform both sheep and mountain lion management in the state of Arizona.
The Santa Catalina Desert Bighorn Sheep Reintroduction was supported by key grants from SCI Foundation, the Arizona Chapter of SCI, and our partner the Wild Sheep Foundation. Other funding came from local organizations, the Pittman-Robertson Act, and conservation auction tags.
Bighorn sheep are a great example of how hunting is conservation. In the 1950s, as few as 25,000 bighorn sheep remained in North America. Today, thanks to restoration efforts led by hunter-conservation organizations like SCI Foundation, there are well over 80,000 sheep across the continent’s mountain tops.
To learn more about this project, watch this video on YouTube.
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