The reintroduction of desert bighorn sheep to the Santa Catalina Mountains north of Tucson continues to move in the right direction. After a successful second release of 30 sheep last fall and a productive lambing season this spring, planning efforts are underway for a likely third release later this year.
This is great news for bighorn — and for everyone who cares about the health and wholeness of the Catalinas.
After a rocky start, the initial group of 31 sheep reintroduced in November 2013 eventually acclimated well to its new home. Mortality was high in the first few months as the sheep explored unfamiliar terrain and were vulnerable to predation, which is common with bighorn projects and wildlife reintroductions in general. Then the surviving sheep coalesced in the prime habitat on Pusch Ridge that had sustained a bighorn herd for many centuries.
Once the translocated sheep began to exhibit their natural social behaviors and use the beneficially rugged terrain on Pusch Ridge, they regained their defensive advantage against predators. After 16 predations in the first four months of the project, nine months passed without a single predation until the second group arrive.
The key in wildlife reintroduction projects is to learn from events on the ground as they play out and modify strategies going forward to give wildlife the best chance to survive and thrive. With the second release last fall, several changes were made based on data and observations collected in the first year.
The chosen release site gave the new sheep a more direct route to encounter the existing herd as quickly as possible. This greatly reduced the time individual sheep spent roaming in areas where they’re vulnerable. Within a couple of weeks, the newly translocated sheep settled in with the previously released group and almost immediately began to benefit from knowledge the fledgling herd had gained.
With the second group, as many sheep as possible were taken from areas of the Tonto National Forest that more closely approximate habitat in the Catalinas (both of which generally have high lion densities). The goal was to bring sheep that might acclimate more quickly to the Catalinas and be more adept at dealing with predators.
The results were startling. Only two individuals from the second group of non-acclimated sheep succumbed to predation, compared to 16 the year before. No lions have been removed in the second year of the project. The icing on the cake was the observance of 16 lambs on the ground this spring, compared to just five the year before.
That kind of success bodes well for the capacity of the Catalinas to support a bighorn sheep herd as it once did. However, it does not guarantee smooth sailing from here on out. It will take years for a self-sustaining herd to become reestablished. Initial projections for this project were for three translocations of 30 sheep each, with good lamb recruitment. The herd must continue to be monitored for disease outbreaks and other threats to its success. And human disturbances — particularly during lambing season — must be minimized through responsible recreation.
This project has already generated a wealth of information on movement, habitat use, lambing locations and other aspects of bighorn behavior in the Catalinas. No doubt more lessons will be learned in the coming months and years, which will be analyzed by leading biologists in the field and applied to the adaptive management of the project.
Some of the tactics may have changed, but the principles of the project remain firm. We seek to restore a key piece of the natural heritage of the Catalinas, while carefully limiting impacts to other species.
We believe that we’ve achieved a good balance, and we’re eager to build on that success. We’re also very appreciative of the broad community support that the project has received. Many Tucsonans have shared their joy in seeing the bighorn back where they belong.