Counting Bats in the San Vicente Redwoods

A Townsend's big-eared bat (Corynorhinus townsendii) has been seen at the San Vicente Redwoods property.

Bats Roost in the Basal Hollows of Redwoods

As the sun goes down, they awaken. Some from within the cavity of a redwood tree. Tiny ones from inside loose bark. The big ones — with wingspans of one foot or longer — emerge from nearby caves. They come out to hunt, to breed, and to migrate.

Migratory Bat Species Frequent Redwood Forests

Love them or hate them, bats are an important part of our ecosystem. They help control insect populations and even pollinate some flowers. And like all of us at Sempervirens Fund, they find solace in and spend a lot of time among the redwoods. The bats we’ve documented are migratory: some come in summer months, others in autumn or winter. Although most research projects on the migration patterns of bats in redwoods have been conducted in Humboldt or Del Norte Counties, researcher Susan E. Townsend, PhD is monitoring bats on our San Vicente Redwoods property. “I’ve detected six species here,” said Townsend. “It’s likely that another six species also inhabit the area, given the similarity of this terrain to other study locations.”

Species Documented in the San Vicente Redwoods

The species Townsend has documented here are the Big brown bat (Eptesicus fuscus), Hoary bat (Lasiurus cinereus), California myotis (Myotis californicus), Long-eared myotis (Myotis evotis), Yuma myotis (Myotis yumanensis), and Mexican free-tailed (Tadarida brasiliensis).” Sempervirens Fund staff have also seen Townsend’s big-eared bat (Corynorhinus townsendii), like in the above photo, elsewhere on the property. While some researchers use nets to catch and release bats or study their droppings, Townsend relies on acoustic recordings. She uses a single Pettersson D500x monitoring device with a microphone secured 20 feet above the ground in a large bay tree. Image of migratory bats found by a recording device hidden 20 feet in a bay tree.

Why Do Bats Love the Redwoods?

We don’t know exactly why bats are drawn to redwoods, but we can speculate. The large basal hollows (openings) — known colloquially as goose pens  — that form at the base of old-growth redwoods from fire may be easy for bats to navigate. Redwood bark is also soft, with deep crags in which smaller species have been found to shelter. For researchers like Townsend, the best place to find nesting bats is around the perimeter of forests near waterways — bats like to rest close to where they hunt. All the species documented in San Vicente Redwoods are insectivores, meaning they eat only insects.

The Importance of Bat Research in Redwoods

Apart from being a great, and possibly spooky, Halloween topic, Townsend’s research on bats shows us once again why protecting redwoods and their environs is such critical and important work. “These species rely on redwood forests for their very survival,” she added. “We need to do more research to know exactly how bats and redwoods are so interconnected.” Why are basal hollows called goose pens, you may be wondering? Early European settlers used them as pens for their geese.

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