Bats About Glen Canyon Park

2012-02-23 at 18-08-20_1 batBats are insect-eating machines. According to the USGS, “Bats normally eat about half their weight in flying insects each night.”  So even for those who don’t find these night-flying mammals charming, it’s good to know there are bats among us.

San Francisco has at least four species of bats, all of which eat insects. According to research by Jennifer Krauel, which involved recording bat sounds to determine which species they were, Mexican Free-tailed bats are the most common. Parks with water – like Glen Canyon – also have Yuma Myotis bats. The other two species she found (more rarely) were Western Red Bats, and Little Brown Bats, and she found them in just a couple of places.

2012-04-07 at 19-41-44 batHer research indicated that “amount of forest edge and distance to water were the factors best explaining species richness and foraging activity.”  It also showed that bats in San Francisco remain active through the winter and don’t hibernate or move elsewhere.

If you’re interested in reading her paper, it’s here as a PDF: Jennifer Krauel thesis on bats in SF


Glen Canyon’s bats are often visible at dusk. They’re most evident in the Fall, though they’ve been seen at other times of the year.  (The pictures above are from February and April, those below from October.)

Here’s a note on bat-viewing from one visitor to Glen Canyon.

“It was late in the afternoon, and late in October. We were standing around the entrance to the park on Alms Rd.  As dusk fell, bats emerged from the tall eucalyptus trees. Quite suddenly they were  in the air right above us. I pulled out my camera, which is not really good in poor light but I tried to take some pictures anyway. Here’s one:

bats 1

“They’re difficult to spot in the picture, but all those black smudges are bats that were moving too fast for my pocket-camera. Here’s the same picture, cropped, with the bats circled in yellow:

bats 1a

“They dispersed over the canyon. Here’s another picture from a few minutes later (and the one below it shows where the bats are).

bats 2

bats 2a

“It was fantastic. I haven’t seen this many bats anywhere in San Francisco.”


We did a little research, and found a Stanford report that emphasized the importance of large trees to a particular species of bats, Yuma Myotis… bats that Krauel’s research had actually found in Glen Canyon Park. 

“Yuma bats that forage in the preserve travel several miles to roost in large trees in Portola Valley and Woodside, suburban communities on the San Francisco Peninsula. The average diameter of the bats’ chosen trees is about a yard across — more than three times wider than the average tree in those areas.”

(The link to the abstract of the actual Stanford research paper is HERE.)

That’s the size of the big eucalyptus trees in Glen Canyon Park – including those that SFRPD wants to chop down.


Bats are an important part of an eco-system, and fill a role few other creatures do: They hunt night-flying insects like mosquitoes that birds don’t catch because they’re sleeping. This is especially important now as West Nile virus, a mosquito-borne disease, has been spreading.

Having bats in a landscape contributes to its bio-diversity. All species of bats are protected in California.

(Some people are concerned that bats carry rabies – and it’s true no one should handle bats, especially grounded bats that may be sick, with their bare hands. But according to the California Department of Fish and Wildlife, less than 1% of bats are infected. [Click HERE to see their note.]  The risk of getting rabies from a bat is less than the risk of being struck by lightning.)


We’re concerned about the impact of the planned tree removals on Glen Canyon’s bats.

  • All species of bats are protected, and removing the trees will impact their habitat by reducing the number of safe roosting spots, especially for Yuma Myotis bats that need both large trees and nearness to water.
  • The contractor will be chopping down the trees in the daytime. Bats roosting there are likely to be killed – if not in the process of the tree-felling, by being forced to fly blinded and confused in the daytime and fall prey to hawks, crows and ravens.

How is SF RPD going to ensure the protection of these bats?

And in what ways will felling large trees near the stream alter the ecology of the canyon?

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8 Responses to Bats About Glen Canyon Park

  1. Barbara Stocklmeir says:

    When Cupertino and the SCC Water District installed the walking/bicycle path between McClellan Ave. and the Blackberry Farm swimming pool area five years ago, they destroyed a bat cave (or whatever they are called) and no one with responsibility cared enough to stop it. And no, I believe the bats have not returned but follow up with the City of Cupertino would be required for verification.

    Once the path is set, it is very difficult to stop. Please keep fighting. I lost and hope you do not. Sincerely, Barbara Stocklmeir Los Gatos, Ca

    Date: Mon, 7 Jan 2013 10:05:54 +0000 To:

  2. Suzanne Berry says:

    I live in New Mexico now, a former resident of San Francisco, and I’m a big fan of bats. There are different species of bats in New Mexico, all of them have a positive role in the environment. Many people build bat houses to welcome these insect eating mammals to their yards. There is also a bat species which pollinates fruit trees in New Mexico.

  3. Alicia Snow says:

    What great photos! A really good post!

    Sent from my iPad

  4. Pingback: Bats in Glen Canyon Park are being evicted NOW! « Death of a Million Trees

  5. Pingback: Glen Canyon Park: What It Looks Like 6 Months After the Trees | Save the Trees of Glen Canyon Park, San Francisco

  6. Pingback: Glen Canyon Park: Six Months after Tree Destruction | San Francisco Forest Alliance

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  8. Pingback: Glen Canyon’s Full of Stairs | Save the Trees of Glen Canyon Park, San Francisco

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