“Free” food: nectar bats at hummingbird feeders in southern Arizona

Abstract

Abstract We report the results of an 11-year (2008–2018) community science project (also known as citizen science) designed to document the use of hummingbird feeders by two species of nectar-feeding bats, the lesser long-nosed bat (Leptonycteris yerbabuenae) and the Mexican long-tongued bat (Choeronycteris mexicana), in the Tucson area of southern Arizona. From 50 to > 100 households participated in this project each year. We supplemented their reports with occasional mist-netting of bats at 21 observer sites to determine age and sex composition of bats at feeders. Our results indicate that L. yerbabuenae was more widespread and common at feeders than C. mexicana, which occurred mainly at sites close to mountains. In the Tucson area, the geographic extent of feeder visitations by bats, mostly L. yerbabuenae, expanded since 2007 and by 2018, covered most of the city and its suburbs. Most bats of both species visited feeders between late August and late October with little year-to-year variation in timing; some individuals of both species continued to visit feeders during winter. The number of bats observed at many sites during September (the month of peak visitations) was relatively stable for at least 10 years; modal numbers of nightly visitors per site in most years was 6 – 10 bats. Capture data indicated that L. yerbabuenae that visited feeders in the Tucson area were not a random sample of the species’ age and sex composition in southeastern Arizona, where their food plants are located in late summer and fall. In Tucson, most bats visiting feeders were subadult females (juveniles and yearlings). We suggest that hummingbird feeders have substantially increased food availability for nectar bats in southern Arizona prior to their migration south into Mexico. However, reasons for the increased use of feeders by L. yerbabuenae, particularly subadult females, beginning in 2007 are not yet clear.