Declining Bat
Populations Imperil
Paul M. Cryan, Michael A. Bogan, and Thomas J. O'Shea
Bat populations are widely believed to be declining.
This decline is of concern because bats are consumers
of vast numbers of insect pests that cost
farmers and foresters billions of dollars. In addition, bats
pollinate flowers and disperse seeds, including those of
agricultural plants such as bananas, breadfruit, mangoes,
cashews, dates, and figs.
In North America, bats pollinate century (agave) plants
as well as giant columnar cacti, including the organ pipe
and saguaro of Arizona. In addition, bats play important
roles as seed dispersers and pollinators on U.S.-affiliated
islands, including flying foxes in the Pacific and New
World fruit bats in the Caribbean.
Three species of bat pollinators occur
in the southwestern United States and
two of these, both long-nosed bats of the
genus Leptonycteris, are listed as endangered
by the Fish and Wildlife Service.
The third species is the Mexican long-tongued
bat, Choeronycteris mexicana,
now termed a species of concern.
Very little is known of the
population status and biology of
this species.
The Mexican long-tongued bat
ranges from Honduras into southern
Arizona and New Mexico. Since
1906, fewer than 500 individuals
have been found in the United
States; nearly all have been females
and young. They migrate from
the South each spring and spend
the warmer months feeding on the
nectar of agave and cactus flowers in
the desert Southwest. While feeding
the bats transfer pollen among plants,
serving as pollinators.
In hopes of learning more about this
species, scientists at the USGS Midcontinent
Ecological Science Center recently initiated a
field survey for Mexican long-tongued bats in
the Southwest under the USGS Species-at-Risk
program. The study involves revisiting sites,
such as mines and caves, where
long-tongued bats were found in
the past. The USGS hopes to
assess current distribution and
numbers of this species, gather
information about behavior and
habitat requirements, and assess
threats to their existence. So far,
long-tongued bats have been verified
in many of the areas of historic
occurrence.
However, much remains to be
learned about the biology of these
curious creatures. For instance, little
is known about how crucial long-tongued
bats are to the pollination and
seed dispersal of the plants on which they
feed. What migratory routes do the bats
follow and are there ample resources along
the way? Why are these bats so infrequently
encountered? Such questions remain to be
answered. Additional in-depth studies into the pollination
biology of Mexican long-tongued bats are
necessary to develop a clearer picture of their precise
role in southwestern desert ecosystems.
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| This Mexican long-nosed bat, Leptonycteris nivalis, hovers above the flowers of a blooming agave. Two species of long-nosed bats feed on the nectar and pollen of agave and cactus flowers in the southwestern United States and Mexico. In the process of feeding, the bats transfer pollen from plant to plant, thus serving as important pollinators. Both species of long-nosed bats are currently on the federal list of endangered species.
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