Bats in the Bypass Return!

With approximately 250,000 Mexican free-tailed bats living under the causeway, the Yolo Bypass Wildlife Area has become a popular place to view these amazing animals.

Referred to as the “extreme bat,” these mammals live in extremely large colonies including the largest colony of any single mammal in the world. They fly extremely high, and have been tracked by Doppler weather radar at two miles high consuming migrating cotton boll worm moths (a.k.a. corn ear-worm moth), army cut-worm moths, and other costly agricultural pests. They are also the jet planes of bat species, averaging 25-45 mph but have been clocked at 99 mph.

Some free-tails stay in the Sacramento Valley all year but most migrate for the winter. They begin returning in large numbers in March and April, with colony sizes stabilizing in May. They give birth to live young from the last week of June to the first week of July, each mother birthing and nursing one pup at most per year. Approximately 25-50% of these young will live through the first year. The pup will begin to fly and learn to hunt at about five weeks of age. Mom will continue to supplement the hunt with milk for another couple of weeks. If the pup can live though one full year, hunting, migrating, and avoiding predation, the animal may live 20 years.

The Yolo Basin Foundation sponsors many tours throughout the summer to watch this nightly event. Each begins with a presentation about bats, followed by viewing of live, non-releasable native bats. After a short break, a caravan is formed to travel through the Wildlife Area to the best viewing spot, which is in the rice fields and not accessible except on tours. The summer schedule is available at www.yolobasin.org. There is a $12 fee for adults.