for National Geographic Today
Scientists are searching for the roosting places of an endangered
species of bat that survives almost entirely on the nectar of agave
The population decline of greater long-nosed bats (Leptonycteris nivalis), which migrate between central Mexico, the Big Bend National Park in Texas, and the southwestern tip of New Mexico, has been attributed to disturbances of the bats' roosting sites and the loss of their food sources.
"There used to be tens of thousands of these nectar bats in the Chisos caves in Big Bend National Park, but these numbers have fallen to somewhere between five and three thousand," said ecologist Brian Keeley of Bat Conservation International in Austin, Texas. He is leading the efforts to find roosting sites along their migratory path.
Many agave crops in Mexico, where the plant is grown primarily for tequila production, have been destroyed by bacterial and fungal diseases. The huge losses have led plantation owners to harvest wild agaves, wiping out the bats' primary food source.
Another threat comes from a public backlash against destruction by vampire bats in Mexico. The response has been general destruction of the roosting sites of many species of bats, including greater long-nosed bats.
"Loss of forests and native wildlife have caused vampire bats to turn to cattle for their meals," said Keeley. "Frustrated ranchers roll smoking tires or set off dynamite in the caves to kill the bats."
Search for Agave Groves
Keeley believes that once the lairs of greater long-nosed bats are found, scientists will gain a better understanding of the size and health of the population. The discovery also should lead to better protection of the caves where the bats roost.
The strategy to seek out roosting sites entails trapping nectar bats in nets suspended in and around the groves of agave, where the bats are expected to feed. The researchers then attach a radio transmitter to each captured bat as a means of tracking it to its roost.
Until now, the only known agave patch and roosting site of these nectar bats in the Big Bend National Park have been in the Chisos Mountains. In June, Keeley and his colleagues surveyed west Texas mountain ranges for more agave groves large enough to attract bats. "We fly low, at about 500 feet (152 meters), and the agaves are big, striking plants that are very easy to spot from a plane," said Keeley.
The agave plant is a blue-green rosette of thick rubbery leaves about three to four feet (one meter) in diameter. When an agave blooms, it sends out a thick woody stalk almost 15 feet (4.5 meters) high, which produces bunches of pale yellow flowers.
"There is a lot of evidence that the bat and agave co-evolved," Keeley explained. "This plant is perfectly tuned to the needs of the bat, releasing its nectar and pollen at 10 p.m., when the bats are out foraging."
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