Busy Summer, into Fall

As we enter fall, this year’s baby bats are now self-sufficiently volant – weaned from their moms, becoming skillful fliers, capturing insects, and learning about their surroundings. Soon, many bats will move away from their summer roosts, either on their way to cold, stable hibernacula, or to locations with moderate winter temperatures where they can retain some degree of activity on warm nights, opportunistically feeding or drinking water.

This is one of the seasonal periods of bat activity when it is appropriate to conduct “take avoidance measures” prior to disturbance or removal of habitat. These could include humane eviction, partial dismantling (under supervision of a qualified bat biologist), or two-step tree removal (again, under supervision, and instruction). That window will close around October 15 in this region, or when night temperatures drop below 40-45F, and/or when rains set in. After that time, bats that remain in roosts will begin to enter torpor, becoming inactive for days or weeks at a time. Winter months are not acceptable periods to remove or disturb bat habitat.

The next seasonal period of bat activity is about March 1 (weather permitting), until about April 15, when females begin giving birth to pups. Throughout the maternity season, until bats become self-sufficiently volant, it is not safe to remove or disturb bat habitat.

This is also the time when we conduct post-construction monitoring of replacement, enhancement, or existing habitat. Here are a couple of photos of a recent survey of extremely successful day/night bat roost habitat which Greg designed for a new replacement bridge.

Piles of bat guano below roost module.

One of four rows of day/night bat roost modules designed by G. Tatarian

Active Projects

As the economy continues to improve, we have been very busy conducting biological surveys in support of vineyard conversions, residential subdivisions, and agricultural expansion projects. We have also been conducting analyses of properties proposed for purchase or sale, to determine applicable California tiger salamander mitigation ratios, in order to satisfy California Endangered Species Act and Federal Endangered Species Act requirements.

California Tiger Salamander

Two Year Study of Artificial Tunnels to Reduce Roadkill of CTS

In 2016 we completed a 2-year study of artificial tunnels beneath Fresno Avenue in Santa Rosa, which were installed to provide safe movement corridors between upland and aquatic habitats for California tiger salamander. The tunnels are coupled with drift fences that redirect salamanders away from the road, which will be connected as a though-street in the future, to reduce or prevent roadkill of this protected species.

Our study was conducted for the U.S. Fish and Wildlife Service to better understand the use of tunnels as a means to reduce mortality of CTS from road traffic.

Effective In-Structure Bridge Night Roost Habitat – Oakville Cross Road Bridge, Napa

The Oakville Crossroad Bridge over the Napa River was built in 1922, and was constructed with materials and a design that made the bridge a highly-visited bat night roost. Greg Tatarian conducted a bat habitat assessment and survey of the bridge under subcontract to Horizon Water & Environment, and provided initial take avoidance and minimization measures, along with mitigation measures for replacement roost habitat.

Planning and engineering was almost complete when the bridge was closed May 22, 2015 as a result of damage from the Napa Earthquake. The emergency nature of the bridge replacement project after the earthquake resulted in a fast-track project that was  completed in about half the time originally planned, but which still incorporated replacement night roost habitat, which Greg designed for bridge engineers and the contractor to implement.

Within a few months of the new (and beautiful) bridge being completed, bats had already begun to return, where they can safely roost at night to rest between foraging bouts.


Beneath the 1922 Oakville Cross Road Bridge. Bats had been night-roosting near abutments.


Newly-constructed bridge with night roost habitat incorporated into bridge deck.

Newly-constructed bridge with night roost habitat incorporated into bridge deck.


The new Oakville Cross Road Bridge with bat night roost habitat beneath deck.

The new Oakville Cross Road Bridge with bat night roost habitat beneath deck.


Evidence of bats night roosting just a few months after bridge completion.

Evidence of bats night roosting just a few months after bridge completion.

Another Successful Bridge Bat Habitat Design by Greg Tatarian


We began working on the Avenue 416 Bridge Replacement Project in Tulare County in 2001, conducting an initial habitat assessment, and then developing measures for avoidance and minimization for take of roosting bats. We updated our work in 2011 as the project was finalized and ready to go to construction; at that time we designed mitigation roost habitat modules and recessed features to be incorporated into the new bridge. Cornerstone Structural Engineering Group handled the engineering and drafting of the sketched details provided by Greg, that feature day roosting crevices and night roosting spaces. Cornerstone had designed decorative soffit details, which Greg modified with additional bat habitat features. Greg then worked with Dokken Engineering to develop and implement safe, effective humane exclusion and eviction of thousands of bats roosting in the original concrete bridge in 2012.

In the first year of post-construction monitoring, Greg observed approximately 4,000 bats, comprised of 4 species – substantially increased over the approximately 1,200 individuals present in the original bridge. Additional monitoring will be conducted by Wildlife Research Associates.

Over water

Heidi J. Williams, Director of Communications for the Santa Clara University School of Engineering, wrote about the project after Cornerstone Engineering Group won an Honor Award from ACEC California. Much of the success was due to the bat habitat, according to Shawn Cullers of Cornerstone, who was also presenting the project for consideration of a similar award on a national level. Click on the thumbnail below for a scan of the article, or go to:


Successful bat habitat design by Greg Tatarian.

Successful bat habitat design by Greg Tatarian.

We Have a New Website!

Our new web site is still under development – thank you for your patience as we complete the work.

Please use the contact form here (click “Read More” button) or on the Contact Us page to send email to Trish Tatarian or Greg Tatarian.


Tatarian design bat house for pallid bats, Brazilian free-tailed bats, Yuma myotis.