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Bats Ignored in Environmental Review for Mace Business Park

2019-12-23_17-43-09Will new ARC SEIR do better?

This letter was sent to Assistant City Manager Ash Feeney on December 23, 2019.

Dear Mr. Feeney,

I am writing to draw your attention to a significant omission in the Mace Ranch Innovation Center Project Final Environmental Impact Report dated January 2016. At no place in the FEIR is there any consideration for Mexican free-tailed bats (Tadarida brasiliensis), or for Hoary bats (Lasiurus cinereus).

Just over 2 miles from the MRIC/ARC site is “One of the largest seasonal Mexican free-tailed bat (Tadarida brasiliensis) colonies in California. An estimated 250,000 individuals strong.” ( This colony roosts under the Yolo Causeway bridge and has been well documented in the Davis Enterprise and the Sacramento Bee (,

I have personally observed bats flying over the MRIC/ARC site during summer months, but there is no mention of bats in the FEIR, or any of the underlying documentation.

Hoary bats have been mist netted by biologists and received into wild rescue by NorCal Bats in the area as well. They generally roost in trees, so it is possible that they roost on the MRIC/ARC site or nearby.

It appears the MRIC EIR Biological Survey missed the bats because it was performed only in winter months when the bats migrate and/or are less active. The Biological Resources Evaluation for the Mace Ranch Innovation Center Project prepared by Sycamore Environmental Consultants in August 2015 indicates the Biological Survey was conducted on December 10.

Bio table
(MRIC-BRE-Aug2015.docx 8/10/2015, Page 9)

Unfortunately, it is very unlikely a survey conducted in December would find the Mexican free-tailed bat or the Hoary bat, because they are migratory and/or dormant in the winter. This information is widely known and publicized. For example, an Atlas Obscura headline, “Bats of Yolo Causeway: Each summer, the migratory bats living beneath the bypass form "batnadoes" at dusk.” (

The Davis Enterprise reported, “About 250,000 Mexican free-tailed bats call the Yolo Bypass Wildlife Area home. Each evening, in the summer, these beneficial animals each [eat] millions [of] insects.” The Yolo Basin Foundation who work to protect and conserve the Yolo causeway habitat area including the bat roost state, “Range: Migratory.”

The Mexican free-tailed bat can fly more than 40 miles a day hunting for food, and they feed on many agricultural pests. There is every reason to believe they are present at the site of the ARC project through the summer months. As stated earlier, I have seen them there myself.

The Hoary bat can travel 24 miles while foraging and could be roosting and/or foraging at the MRIC/ARC site in the spring and fall.

Also, there is no information in the Biological Resources Survey as to the time of day of the biological survey. A survey done during daylight hours would also make it unlikely to find bats since they are nocturnal and emerge to hunt at the MRIC/ARC site only at twilight.

Additionally, there are known summer nesting sites for heron and other birds near road 105. These birds may also be foraging in the summer months on the MRIC/ARC site and would have been missed with a December survey.

New Biological Surveys in the spring, summer and fall months at the proper times must be done to assess the presence of Mexican free-tailed bats, Hoary bats, and summer migratory birds so that proper mitigation measures can be planned.

It is also notable that these bats are a food source for Swainson’s Hawks, a designated Threatened Species in California, so knock-on impacts on the hawks resulting from impacts on the bats must also be considered.

Although Tadarida brasiliensis, “is widely regarded as one of the most abundant mammals in North America, and is not on any Federal lists… its proclivity towards roosting in large numbers in relatively few roosts makes it especially vulnerable to human disturbance and habitat destruction.” Since this major roost is so close to the ARC site, the potential impacts on the roost must be understood and mitigated before moving forward with the project.

( The Western Bat Working Group further notes “Documented declines at some roosts are cause for concern.” Bat Conservation International (BCI) notes, “The world is a dangerous place for bats. Although they provide vital environmental and economic services, bat populations are declining around the globe, largely as a result of human activity… Loss of habitat remains the most widespread peril worldwide.” (

BCI also reports that bats are further threatened by White-nose syndrome: “over 5.7 million of bats have been killed by White-nose Syndrome, a wildlife disease that continues its spread across the continent. Caused by a cold-loving fungus called Pseudogymnoascus destructans, WNS attacks hibernating bats, causing mortality rates that approach 100 percent at some sites.” WNS was announced in CA last summer in Plumas County. Now that it has arrived in CA it could rapidly decimate the remaining bat populations.

2019-12-23_17-43-09BCI further reports that, “The dramatic growth of wind energy throughout much of the world is also taking a huge toll on bats.”

“The cumulative impact of wind power facilities in killing migratory bats threatens to become an environmental crisis that cannot be ignored (O’Shea et al. 2016). By 2012, more than 600,000 bats were being killed annually, and the number grows each year (Hayes 2013).”

“Scientists estimate that hundreds of thousands of bats are killed each year in the United States by collisions with the spinning blades of wind turbines or rapid pressure change at turbines that can rupture blood vessels. BCI and its partners have been working since 2004 to minimize bat fatalities at wind sites” according to BCI.

These impacts of renewable energy generation on bats is a point of concern in relation to the ARC project. On April 14th, 2016 the Davis Enterprise published this illustration of the MRIC/ARC project provided by the developer. ( The illustration clearly shows the developers are considering placing several wind turbines at the project.


The illustration was used again in the California Aggie on December 10, 2019 in what appears to be a developer press release story. (

The inclusion of wind turbines in the project is also supported in the ARC PPD zoning changes. The Aggie Research Campus – Proposed Preliminary Planned Development (PPD) specifically adds a permitted use, “(f) Renewable energy generation and storage facilities” This did not appear previously in the MRIC PPD and constitutes a change that must be studied in the SEIR. This land use designation also does not exist in the current Davis Municipal code and thus lacks definition. It certainly can be read to include wind energy generation.

Renewable energy generation at the ARC site needs to be studied in the EIR. In order to understand its impacts, a new Biological Survey needs to be performed in spring, summer, and fall months. The biological survey that was conduct on only one day in December was not a sufficient biological study to base the MRIC FEIR on and clearly missed biological resources on the site. Even if no wind generation is planned for the site, a proper biological survey that can determine the presence in spring, summer, and fall of migratory animals including bats needs to be done before this project can move forward.


Colin Walsh


Roberta L. Millstein

I just looked up those two bat species, here:

One of them, Lasiurus cinereus (hoary bat) is a California species of special concern.

This is a major oversight of the previous environmental analysis. It had better be corrected in the upcoming one.

Alan Pryor

The developers also did their Burrowing Owl survey in the winter months instead of breeding months as recommended by the California Dept of Fish and Wildlife. Thus, the surveyors missed the colonies immediately adjacent to the site and the EIR misleadingly stated there were no Burrowing Owls and proposed no mitigation. They were dutifully notified of this oversight by the Burrowing Owl Preservation Society.

Ron O

Colin: As always, I appreciate your efforts.

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