April 2, 2015. Bats have been spotted under the Campbell Ave. bridge at the Rillito River. You can view the bats fly out from under the bridge at sunset. Here is a classic librarian file on the subject.
From the Librarian Files
Bats in Tucson
Mexican free-tail bats are common in Tucson. These bats migrate from Mexico to Tucson in April. The bats return to Mexico in October. Mexican free-tail bats are small animals weighing about 13 grams, with a wingspan of 10 inches and a body the size of a human thumb.
The expansion joints of Tucson’s bridges provide a perfect home for these bats. The 1 foot-deep groves give the bats an ideal location for their young because the temperature remains consistent. Five hundred baby free-tail bats can cluster in 1 square foot under the bridges.
There are 4 bridges in Tucson that have big colonies of bats:
East Broadway bridge over the Pantano Wash.
North Campbell Avenue bridge over the Rillito.
East Tanque Verde bridge over the Rillito.
Ina Road bridge at the Santa Cruz River.
At sunset the bats fly out from under these bridges.
In 2008 it was estimated that there were up to 200,000 bats flying around Tucson. The bat colony under the Pantano wash bridge was estimated to contain 20,000 bats. So it was estimated that the Pantano bat colony eats 2 tons of insects during a season.
There are other bats that are also seen in Tucson: Pallid bat, Silver-haired bat, Cave myotis, California myotis, Yuma myotis, Western pipistrelle and the Big Brown bat.
Occasionally, the Lesser long-nosed bat is found under Tucson bridges. This bat does not feed on insects, but rather on the agave plant.
All bats are protected by Arizona state law and some of these bats are protected by the federal Endangered Species act, so it is illegal to disturb or harm bats.
To be safe, watch the bats from a distance. Never pick up a live bat on the ground. A live bat on the ground is a bat with problems, possibly rabies. A live bat on the ground should be reported to Pima County Animal Control.
"Sunset bat launch from bat bridges an urban bat spectacle." Arizona Daily Star. July 14, 2008. Page 1.
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