Red Cliffs Desert Reserve looks at new protocols to better determine raven threat to tortoises

ST. GEORGE — Wildlife officials are looking at new ways of determining just how much of a problem ravens may be for the area’s threatened Mojave desert tortoise population.

Raven up close, location and date unspecified | Image by LoggaWiggler from Pixabay, St. George News

“We really need to find out how big of a problem we have on our hands,” Mike Schijf, biologist for the Red Cliffs Desert Reserve, told the Washington County Habitat Conservation Advisory Committee last week.

The committee, which directs the management on the Red Cliffs Desert Reserve and its accompanying habitat conservation plan was updated on new protocols to be used for the reserve’s raven monitoring program starting this year during its March 23 meeting.

The monitoring program started in 2015, Schijf said. A recorded 34 desert tortoise remains attributed to raven predation have been found since, with around half of those instances being recorded in 2019. Much of that predation took place near a known raven nest site on Red Mountain near Ivins.

Various raven control measures have been considered, including a practice called “egg oiling,” Schijf said.

Egg oiling involves putting vegetable oil on raven eggs, which in turn suffocates the embryo inside. The practice is considered a humane method of bird population control. He said added benefits are limiting the number of new ravens that are being taught to prey on smaller tortoises and possibly getting the ravens to think the area they’ve chosen to nest isn’t viable for egg-laying.

In this 2019 file photo, a map of the Red Cliffs Desert Reserve showing known raven nest site and areas of desert tortoise predation, St. George, Utah, Oct. 23, 2019 | Photo by Mori Kessler, St. George News

However, before going ahead with the potential use of egg oiling or other lethal means of raven control, Schijf said desert reserve staff need to collect more data on the birds to determine if they are really as big as a threat as previously believed.

New protocols Schijf said the reserve’s raven monitoring program was planning to implement will bring it more in line with what other tortoise reserves have done in California and Nevada. These new protocols, developed by U.S. Fish and Wildlife biologist Kerry Holcomb out of California, involve point surveys for raven density and bait stations meant to record if ravens in certain areas are feeding on juvenile tortoises.

The point surveys would occur in 10-minute intervals in select areas across Washington County and ultimately help estimate the density of the county’s raven population. If the density is determined to be more than 0.4 ravens per kilometer, there is a “significant problem,” Schijf said.

As for the bait stations, these take the form of what Schijf called “techno-tortoises.” They fake, 3D-printed juvenile tortoise shells that would be anchored to the ground and monitored by a camera to see how often ravens in a particular area may attack them thinking they are a food source.

Examples given on a slide of the 3D-printed “techno tortoise” shells that would be use in bait stations to help determine if ravens in the are are attacking and eating juvenile Mojave desert tortoises, St. George, March 23, 2021 | Photo courtesy of the Red Cliffs Desert Reserve, St. George News

Having the bait stations handy will be beneficial as it will provide evidence of predation instances that may otherwise go undetected, Schijf said. Baby tortoise shell remains can easily disappear within three-to-four days, thus preventing an accurate estimate on suspected raven attacks, he said.

“We think this is important,” Schijf said. “Maybe we don’t have a raven issue. This will help us find out.”

However, there are potential complications to implementing the new raven monitoring protocols.

Holcomb’s plan recommends setting up 117 point survey spots and 21 boat station spots across the county. This will require coordination with the Bureau of Land Management in order to gain access to certain areas the federal officials may otherwise not want disturbed. This, among other factors, will likely necessitate a reduction in the recommended number of desired point survey and debate station locations.

“We want to do this in a delicate way,” Schijf said. “We want to work with everyone and make sure this is done right.”

The windows of opportunity for the new raven monitoring protocols to take effect are from April 10 to May 19 for the 10-minute point surveys, and April 24 to May 7 for the “techno tortoise” bait stations.

Copyright St. George News, LLC, 2021, all rights reserved.

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