Tuesday, October 27, 2009

Following pallid bats in canyonlands of southeastern Colorado

telemetered Antrozous pallidus
Pallid bat (Antrozous pallidus) with attached telemeter (gleaming line behind the bat is the antenna from the transmitter)

The pallid bat (Antrozous pallidus), like most bats in North America, feeds on invertebrates, but pallid bats are one of the few that takes a considerable proportion of their meals off the ground or vegetation. Pallid bats can sometimes be found landing on the ground to capture and eat terrestrial arthropods, like scorpions, centipedes, spiders and grasshoppers. Pallid bats are mainly nocturnal, and during the day can roost in large aggregations of hundreds of individuals. Most often, however, day roosts contain solitary bats or small groups of individuals in caves, mines, cracks or buildings.

Antrozous pallidus roost
Jeremy Siemers sitting above a boulder where a pallid bat is roosting (the bat is in the crack in the foreground)

CNHP Zoologists Rob Schorr and Jeremy Siemers spent this summer trying to determine what areas male pallid bats use during the day. As the sun set near the Purgatoire River in Las Animas County, Rob and Jeremy extended mistnets over cattle troughs in hopes of catching bats flying in for a drink. Twelve male pallid bats were captured over several troughs, and Rob and Jeremy carefully attached radiotelemeters to each one. The radiotelemeters emitted high frequency sound that could be tracked using specialized antennas and receivers.

Antrozous pallidus telemetry
Rob Schorr and telemetered pallid bat

Rob, Jeremy, graduate student Jessica Healy, and technician Catherine Gearhart tracked these 12 pallid bats to approximately 50 roosts. Most of these roosts were in tall, vertical cracks in rock wall cliffs, but a few were in the cracks of large boulders. Some roosts were home to multiple bats and on two occasions one of the telemetered bats was found using a roost previously occupied by another telemetered bat. What became apparent over the course of tracking the pallid bats is that the bats selected cliff roosts that were difficult for humans to access. On more than one occasion researchers had to backtrack after reaching perilous cliff walls or drop-offs. As Rob and Jeremy analyze this summer's data, it will be interesting to discover if the roosts of these 12 bats display similar characteristics.

pallid bat roosting habitat
Jeremy Siemers peers from one of the cliff wall cracks near a pallid bat roost

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