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Radio telemetry data on nighttime movements of two species of migratory nectar-feeding bats (Leptonycteris) in Hidalgo County, New Mexico, late-summer 2004 and 2005

September 28, 2017

These bat location estimates have been reported by Bogan and others (In press) and come in the form of a GIS shape file. Three species of nectar-feeding phyllostomid bats migrate north from Mexico into deserts of the United States (U.S.) each spring and summer to feed on blooms of columnar cacti and century plants (Agave spp). However, the habitat needs of these important desert pollinators are poorly understood. We followed the nighttime movements of two species of long-nosed bats (Leptonycteris yerbabuenae and L. nivalis) in an area of late-summer sympatry at the northern edges of their migratory ranges. We radiotracked bats in extreme southwestern New Mexico during 22 nights over two summers and acquired location estimates for 31 individuals. During July and August of 2004 (13 nights) and 2005 (15 nights), we attempted to continuously monitor for signals of radiotagged bats from dusk to dawn using fixed telemetry stations and standard radio telemetry procedures. We estimated bat locations from 2 or more simultaneous (plus or minus 5 sec) radio bearings. All locations were estimated using a Maximum Likelihood Estimation (MLE) technique. We captured a total of 34 L. yerbabuenae (13 adult females, 19 young-of-year, 2 adult males) and 25 L. nivalis (15 adult females, 3 young-of-year, 7 adult males) in 2004 and 2005. We attached radio transmitters to 27 L. yerbabuenae and 19 L. nivalis, then obtained sufficiently precise location estimates (less than or equal to 10 square km) for 31 individuals. We discerned movements of 19 L. yerbabuenae, with each tracked an average of 2.4 nights, and obtained an average of 8.5 location estimates per bat per night. We followed 12 L. nivalis, with each bat tracked an average of 1.3 nights, and obtained an average 5.3 location estimates per bat per night. Three of the tagged bats (2 female L. yerbabuenae and 1 male L. nivalis) were not detected consistently enough to derive sufficiently precise location estimates. We suspect that the 13 bats we never detected after tagging (7 L. yerbabuenae and 6 L. nivalis of various sex and age groups) either left the study area, removed their transmitters, or the radio transmitters malfunctioned. Over 5,000 person-hours of effort and 300 hours of continuous tracking resulted in more than 5,000 bearings taken, of which 4,837 were simultaneous with at least one other and were used in the estimation of 1,296 bat locations. Bats flew throughout the night, although we observed a decrease in detection near the middle of the night in both species. We estimated 640 locations using 2 bearings and 656 using 3 or more bearings. The average number of bearings used per location estimate was 2.7. The size of error ellipses, which indicated the 95-percent confidence area of location estimates, were variable: 69 percent (n = 900) of estimates had error less than or equal to 100 square km; 60 percent (n = 772) had error less than or equal to 50 square km; 48 percent (n = 627) had error less than or equal to 25 square km; 33 percent (n = 426) had error less than or equal to 10 square km; and 13 percent (n = 172) had error less than or equal to 1 square km. Both species cohabitated two major day roosts that were 30 km apart and in different mountain ranges, yet individual bats sometimes moved between the roosts. Sampling was opportunistic and limited, but there were no obvious qualitative differences in observed patterns of movement between species or years, or among sex, age, and reproductive groups. Both species were observed foraging most often in the mountain range with a relatively higher observed density of presumed food plants (Agave palmeri); when roosting in an adjacent mountain range, bats sometimes commuted more than 20 km one-way to forage. Contrary to evidence indicating these species partition resources farther south in Mexico, our findings suggest that L. yerbabuenae and L. nivalis seasonally share common roost and food resources during late summer in this northern area of sympatry. These data are reported in detail in the paper:

Bogan, Michael A.; Cryan, Paul; Weise, Christa D.; and Valdez, Ernest W. (2017) "Landscape movements by two species of migratory nectar-feeding bats (Leptonycteris) in a northern area of seasonal sympatry," Western North American Naturalist: Vol. 77 : No. 3 , Article 4.