Whispering Ranch Mine - Bat Gating Project
Located on BLM Land outside of Wickenburg, Arizona.

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Before doing any work at a mine site, the Bureau of Land Managemant (BLM) first goes through a series of processes to decide what is the most appropriate plan to manage that site. During this process Jason Corbett of Bat Conservation International (BCI) and Bill Burger of the Arizona Game and Fish Department (AZGFD) were brought in to do an underground inventory of this abandoned mine. During the underground inventory it was discovered that the mine was a warm season roost for a colony of California Leaf Nosed bats (Macrotus californicus). Subsequent surveys by the AZGFD revealed that the shaft was also being used during the winter making the site even more worthy of protection. This bat plays a really important role in reducing insect populations in the area and throughout the southwestern US. Additionally, during the mine inventory Jason and Bill discovered that Barn Owls were not only roosting in the mine but also nesting. The owls are advantageous to the local area because they reduce rodent populations. It is probable that the bats and owls are roosting at different times of the year, but they both play an important role in controlling pests in the neighborhood. The fact that these two species use the mine as habitat strongly supported the gating and protection of this unique site.


California Leaf Nosed Bat

California Leaf Nosed Bat (Macrotus californicus)


Cupola Bat Gate

Cupola Gate Cutaway View


After taking measurements at the mine site, and discussing various gating options, we began our design of the gate. The primary goals of human safety and wildlife access were the central focus, but a variety of other criteria also drive the gate design. Since the California Leaf Nosed bat is a very agile flyer and the fact that they are flying straight up a deep vertical shaft, we decided to implement a Flyway Roof where the bat can fly directly vertical out of the gate. This design helps the bats avoid predation at the gate since they don't have to slow down while passing the bars. Another design feature that we added to this gate is the Stability Apron. Sections of the collar of this mine consisted of loose rock that might collapse in the future. To avoid potential holes around the bottom of the gate we extended a wide steel Stability Apron at least 3 feet around the entire base of the gate. This apron also acts as a steel footer discouraging vandals from digging under the gate, and avoids the time-consuming onsite construction of a more traditional concrete footer. In order to provide bat researchers with access to the roost, we included an entryway door in the center of the top of the gate. At this location a rope rigged to the gate will freely drop down the center of the shaft without touching walls, thus avoiding potential rockfall while descending the pit. As shown in the following drawing, the gate is recessed below the immediate ground surface. This was done for two primary reasons. First, the surface fill consisted of waste rock from the mine which was somewhat loosely compacted. By digging down to original underlying rock, we had a better foundation to pin the gate to the ground. The second reason is to hide the gate from easy view from casual onlookers driving along adjacent roads.


Once our gate design was complete we began construction of the gate at our shop in Tucson, Arizona. When possible we prefer to build our gates in a workshop instead of on-site construction. We've found that we can build gates quicker and with higher quality in a shop. Due to the size of this gate we decided to build the gate in three sections. This also made the gate small enough for trailer transport to the mine site. Weighing in at around 5,000 pounds we used our shop's chain hoists to move the gate around during construction. Since this gate site was in an area that could be prone to vandalism and attacks we built the gate with heavy materials and two types of steel. The frame structure was built of heavy ¼ inch mild steel. The bars, and bar mounts were built of work hardening Manganal Steel. The result was an extra strong gate that would be very difficult to vandalize.


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Bat Gate on Trailer

Gate Loaded on Trailer at the Shop


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