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It has been more than 30 years since the Ramona grasslands ecosystem has seen a self-sustaining colony of Western burrowing owl (Athene cunicularia ssp. hypugaea). 

That is changing! 
 
San Diego Habitat Conservancy (SDHC) manages the Ramona Grasslands Conservation Bank (RGCB Preserve), which is the translocation site of a new population node for the western burrowing owl (BUOW) that is a California Species of Special Concern and is federally listed as a Bird of Conservation Concern. The San Diego Zoo Wildlife Alliance (SDZWA) examined several conserved locations for suitable habitat to translocate and establish a population of BUOW. In 2020, the RGCB Preserve was selected for the translocation of BUOW due to SDHC’s long-term commitment to benefit BUOW and their habitat. To date 40 BUOW (24 in 2021 and 16 in 2022) have been brought to the site and more than 20 juveniles successfully fledged in 2021. The 2022 nesting season looks promising with several owls that stayed from 2021 pairing with the new arrivals. An additional 10 or more BUOW are anticipated to be brought to the site in 2023. This project that has been in planning for more than a decade through the Multiple Species Conservation Plan will give the BUOW a chance to come back to the Ramona grasslands ecosystem and hopefully thrive for generations to come. For a video summary and other articles see the News tab of the SDHC website https://www.sdhabitat.org/news.html

The 210-acre RGCB Preserve is part of more than 4,000 acres of conserved land and includes vernal pools that support the Endangered San Diego fairy shrimp (Branchinecta sandiegonensis) and rare plant assemblages that bloom in the spring. Portions of the RGCB Preserve are Critical Habitat for the Endangered arroyo toad (Anaxyrus californicus) and Stephens’ kangaroo rat (Dipodomys stephensi). The rare southern tarplant (Centromadia parryi  ssp. Australis) and graceful tarplant (Holocarpha virgata ssp. elongata) occur on the site and an incredible diversity of raptors frequent the area.
 
Burrowing owls are small, typically only growing to be about 10 inches in height. Their feathers are brown and white and true to their name, they live in burrows usually created by other animals, such as the California ground squirrel (Otospermophilus beecheyi). Their large yellow eyes, a defining characteristic for owls, give them the ability to see and hunt small prey items in the dark such as small mammals, though they feed on insects during the day as well. They are the prey of many species including other raptors such as peregrine falcon (Falco peregrinus), great horned owl (Bubo virginianus pacificus), and red-tailed hawk (Buteo jamaicensis), as well as American badger (Taxidea taxus), long-tailed weasel (Mustela frenata) and coyotes (Canis latrans), if they can catch them. Burrowing owls were once considered widespread and abundant in the San Diego area but have declined over the last decades due to habitat loss, rodenticides and are considered at risk of being lost even on conserved lands. 

 

 

Preparations for Translocation

To prepare for the translocation to the site, artificial nest chambers and burrows were created to mimic the living quarters of these underground denizens. Each artificial burrow box is made of cedar planks and buried underground out of sight. Twenty-six artificial nest chambers were strategically buried to ensure flooding does not occur during rains and to optimize the space for a colony to occupy. The boxes, buried below the earth also keeps them cool during hot days and warm during cool nights. 

These boxes have multiple entry and exit holes that connect to drainage piping that serves as tunnels for the owls to enter, exit and escape predators. Along each tunnel, there is a dip in the pipe to act as a water catch for extra protection from flooding. Chicken wire mesh is used to cover all access entry points to deter canid predators from digging up the entryways. Additionally, rocks are placed at the entry to deter predators. Vegetation especially around the entrances is controlled with help from local cattle grazers. Each burrow is large enough for a breeding pair to have multiple clutches, with room to feed and rest. Average box size is 18”x18”x12”, with the entry extending about three feet from the boxes.

After the artificial nest chambers and burrows were installed, temporary aviaries (large flight cages) were built to house the owls. The aviaries are left up for two to four weeks and then removed. The time spent in the aviaries enables the owls to acclimate to the area and hopefully some will even lay eggs, which almost ensures that they will stay. Stereos were set up to play recorded BUOW calls and coos, to encourage colony forming.

Rocks are painted with what looks like owl feces to convince relocated burrowing owls to stay at their new homes. After the owls are released, SDZWA monitors the health and nesting progress of the owls and provides supplemental feeding for the first nesting seasons. SDHC assists with this monitoring and will be monitoring numbers of owls on site in perpetuity.

Above and Beyond! 

SDHC goes Above and Beyond required habitat management.  Below are a few examples. 

Eucalyptus Removal
Prior to 2020 the Grassland Preserve had a 5-acre grove of Eucalyptus trees that had grown into spindly, tall, diseased trees that were being used primarily by great horned owls that prey on both juvenile and adult BUOWs. To reduce the risk of predation to the new colony, SDHC, with financial assistance from the Natural Resources Conservation Service, cut down more than 200 trees. 

Brush Piles 
With the assistance of many volunteers including our local Audubon Chapter, the downed wood from the Eucalyptus trees was used to make brush piles. Brush piles provide cover that has been shown to act as refugia for California ground squirrels that burrow in and around the brush piles. These burrows are then, in turn, used by the owls. 

Mulch
The adorable but predatory long-tailed weasels are known to the area and like to utilize the downed eucalyptus trees for cover. To reduce the cover and weasel populations, the trees were mulched. BUOW are plagued with a common poultry pest: sticktight fleas(Echidnophaga gallinacea). Eucalyptus is speculated to repel these pests, so eucalyptus mulch has been spread near several burrows. These burrows with nests will be monitored. If mulching is successful to repel sticktight fleas, this method may be implemented at other BUOW management sites. 

All of this preparation will certainly help these populations of reintroduced owls as much as possible. Future generations of the burrowing owl onsite will have to do more on their own but with SDHC’s management help will be better equipped to do so. 

Get involved!! 

Volunteer
SDHC welcomes volunteers to assist with special projects and some general monitoring. Visit https://www.sdhabitat.org/volunteer.html for more information. 

Don’t Use Rodenticides
Rodenticides are commonly used to rid homeowners of rats, mice, squirrels, and other rodents. When rodents become ill after ingesting the rodenticide, they are easily eaten by predators, and the chemicals infiltrate the next level in the food web, including raptors. Raptors, including BUOW that are found ill or diseased have high levels of many of the rodenticides in use today.

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