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Overwintering Burrowing Owls at WERC

In Partnership With Talon Ecological Research Group

The Western Burrowing Owl has been experiencing significant declines throughout its range and especially in Santa Clara County. This denizen of short grasslands that lives in the burrows of fossorial mammals, especially California ground squirrels in California, has declined for several reasons: loss of grasslands, eradication of ground squirrels, high predation rates, and low reproductive rates due to a combination of factors such as low-quality prey availability and fragmented habitats.


The Project

Burrowing owls are a covered species for the Santa Clara County Habitat Agency (Habitat Agency) and as such the Habitat Agency has contracted with Talon Ecological Research Group (Talon) to conduct in-depth research and conservation efforts to reverse the decline of burrowing owls in Santa Clara County and adjacent areas (study area).
Since 2014, Talon has been monitoring burrowing owls in the county with breeding and wintering season surveys, banding of owls to provide each individual a unique identification code, and photo monitoring using motion detection wildlife cameras. The results of these monitoring efforts show a sharp decline in the burrowing owl population from a total of 116 adults in 2014 to only 35 adults in 2020 (Table 1):


Burrowing Owl Chart - Table 1

To reverse the decline of burrowing owls within the study area, the Habitat Agency and Talon are implementing several research and conservation projects to understand burrowing owl ecological requirements and attempt to increase the population. Conservation projects include the following:

  • Habitat enhancement with vegetation control at two breeding locations, installation of artificial burrows, removal of non-native invasive weeds, and planting of native species to increase the prey base.

  • Supplemental feeding of burrowing owls during the breeding season to increase reproductive success.

  • Banding of burrowing owls to monitor breeding success, mate selections, movement patterns and longevity.

  • Photo monitoring to determine breeding success and predator impacts.

  • Captive breeding to increase the population and reduce inbreeding.

  • A Juvenile Overwintering Project to reduce predation rates of burrowing owl juveniles that can be as high as 70% during the first year of a burrowing owl’s life, and relocate breeding pairs of owls to sites to increase the source population.


The Juvenile Overwintering Project has proven to be a very successful conservation effort to successfully reduce the mortality rates of young burrowing owls and increase breeding populations at existing sites and in the very near future help create additional breeding populations at new sites. The project involves the capture of juvenile burrowing owls at existing breeding sites when the young burrowing owls are almost ready to fledge the nest burrow. The juvenile burrowing owls are then overwintered in a facility where they are fed a diversity of prey items, and their health is monitored on a regular basis to ensure they are in perfect condition. At present, the Peninsula Humane Society (PHS) in Burlingame overwinters the burrowing owl population, however, based on the success of the program over the past two years we are expanding the program and the Wildlife Education and Rehabilitation Center (WERC) in Morgan Hill will provide an overwintering facility for the additional burrowing owl juveniles starting in 2021. During July of 2021, WERC will receive juvenile burrowing owls that will be housed at their facility until February or March of 2022. These juvenile burrowing owls will be fed small rodents and a variety of invertebrates and their health monitored for the duration of their stay at WERC. Special enclosures will be constructed to facilitate the project to provide maximum exercise for the juvenile owls. During December of 2021, the burrowing owls (adults at this stage) will be separated by gender (during the banding process feather analysis allows gender identification of each individual) in preparation for the approaching breeding season. Blood samples from the burrowing owls will permit genetic analysis of each individual to determine which two burrowing owls will form a breeding pair to reduce inbreeding in this very small local population.In February and March of 2022, Talon will choose a release site for the burrowing owls, artificial burrows will be installed and a hacking enclosure assembled over the artificial burrows and a breeding pair of burrowing owls will be released from WERC into each enclosure. The burrowing owls will remain in the enclosure where they are fed for thirty days until they produce eggs. After thirty days, the enclosure is removed and the breeding pair of burrowing owls will be monitored for the duration of the breeding season. This conservation project has already occurred with great success for the past two years at two existing breeding locations in Santa Clara County. With the conservation efforts of WERC, Talon, and the Habitat Agency, the next goal of the project is to release burrowing owl breeding pairs at new sites within the county to establish additional breeding populations to increase the population and reverse the decline of burrowing owls. 


Talon Ecological Research Group- Owl Conservation in Santa Clara County. Write up by Phil Higgins

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