TIMING OF AGAVE PALMERI FLOWERING AND NECTAR-FEEDING BAT VISITATION IN THE PELONCILLOS AND CHIRICAHUA MOUNTAINS

Palmer's agave (Agave palmeri), prominent in semi-desert grasslands of Arizona, New Mexico, and northwestern Mexico, shares its range with migratory nectar-feeding bat species and has bat-adapted floral traits. However, previous observations suggest that bats, such as Leptonycteris curasoae, often miss much of the lengthy flowering period of A. palmeri. To test the hypothesis that peak flowering coincides with peak availability of bats, I monitored flowering in 2 areas from mid June to mid September 1997, observed plants with night-vision binoculars for signs of pollinator activity, and measured floral rewards during part of this period. In the Peloncillos Mountains, New Mexico, no bat visits were seen during the first 60% of the flowering period (15 June to 12 August), and large dawn standing crops of nectar and pollen indicated little nocturnal consumption. From 24 August to 12 September, as the number of flowers decreased, bats were common visitors. These included L. curasoae and Choeronycteris mexicana. In the Chiricahua Mountains, Arizona, results were similar except that bats were also seen once in July. These observations suggest that most bats arrived late in the flowering period. However, detecting bats during peak flowering is problematic, because their energy needs are low relative to agave rewards, and a small population could be easily satiated.