Prey Selection by a Neotropical Foliage-Gleaning Bat, Micronycteris megalotis

May 1980 GENERAL NOTES 327 MAN. 1954. The role of thermal radiation in animal ecology. Ecology, 35:562-568. MILLER, L. 1955. Color change in the black bear, Ursus americanus. J. Mamm., 36:460. ROGERS, L. L. 1976. Effects of mast and berry crop failures on survival, growth, and reproductive success of black bears. Trans. N. Amer. Wild!' Nat. Res. Conf., 41:431-438. 1977. Social relationships, movements, and population dynamics of black bears in northeastern Minnesota. Unpuh!. Ph.D. dissert., Univ. Minnesota, Minneapolis, 194 pp. ROGERS, L. L., ET AL. 1976. Characteri~tics and management of black bears that feed in garbage dumps, campgrounds, or residential areas. Pp. 169-175, in Bears-their biology and management (M. R. Pelton, J. W. Lentfer, and G. E. Folk, eds.). IUCN PubI., New Series, Morges, Switzerland, 40:1-467. SWAIN, A. M. 1973. History of fire and vegetation in northeastern Minnesota as recorded in Jake sediments. Quaternary Res., 3:383396. TRUE, F. W. 1882. On a cinnamon bear from Pennsylvania. U.S. Nat!. Mus., 5:653-656. VAN WORMER, J. 1966. The world of the black bear. l B. Lippincott Co., Philadelphia and New York, 163 pp. WRIGHT, H. E., JR. 1968. History of the prairie peninsula. The Quaternary of Illinois. Spec. Pub!., Vniv. Illinois College Agric., 14:1-179. WRIGHT, H. E., JR., ET AL. 1969. Glacial and vegetational history of northeastern Minnesota. Pub!. Minnesota Geoi. Surv., 11:1-59. LYNN L. ROGERS, U.S. Department of Agriculture, North Central Forest Experiment Station, 1992 Folu;ell Avenue, St. Paul, MN 55108. Submitted 27 March 1979. Accepted 25 September 1979. }. Mamm .• 61(2):324-327. 1980 PREY SELECTION BY A NEOTROPICAL FOLIAGE-GLEANING BAT, MICRONYCTERIS MEGALOTIS The feeding habits of most insectivorous bats are probably a combination of opportunism and selective predation, varying with local conditions such as the relative abundance of different kinds of insect prey (see Whitaker and Black, 1976; Fenton, 1975; Fenton et aI., 1977; Kunz, 1974). Here we present data on the food habits of Micronycteris megalotis based on insect fragments collected from under two night roosts used solely by this species. Micronycteris mega/otis, one of the smallest (ca. 7 g) and most common species in this genus, occurs in a variety of habitats from Mexico into South America. Little is known about its food habits. and it is not clear from the literature if the species feeds mainly on fruit or on insects (Gardner, 1977). During late 1973 and 1974, we classified more than 5,000 insect fra~'Illents collected from two night roosts at Finca La Selva in Costa Rica (see site descriptions in Orians, 1969; Fleming, 1974; and LaVal and Fitch, 1977). Most of the fragments were obtained from about 3 m inside a hollow log of 1 m inside diameter, and the others were swept from under a bed in a house. To f.'-K:ilitate collecting the remains in the log, we placed a plastic sheet in the hollow under the night roost and removed the fragments from it. Collections were made in late September and early October (lumped), mid-November, late December and early January (lumped), late January, mid-February, and June. Although most of the fragments were wings and legs, only the wings, plus a few whole bodies, were counted. The percentages in Fig. 1 and the numbers in Table 1 were obtained as follows: where forewings and hindwings were matched and identified, the larger of the two counts was used (Orthoptera, Homoptera, Hemiptera, and Coleoptera); when forewings and hindwings could not be reliably distinguished (Lepidoptera, Odonata, and Hymenoptera), the figures were divided by two. In other orders, the total number of wings was counted; in all cases, bodies were counted as two wings. Redundant pieces, such as orthopteran legs, were not included in the number of fragments (>5,OOO) given previously; all identifications were made to the level of family where possible. A rough approximation of numbers of insects consumed could be obtained by dividing in half ali wing counts shown in Table 1. However, our samples contained numerouS unmatched wings, leading us to believe that the bats dropped some insect wings before arriving at the night roost. Downloaded from https://academic.oup.com/jmammal/article/61/2/327/903740 by guest on 09 March 2021 328 JOUR NA L OF MAM MALOGY Vol. 61, No . .2 0' .'" alt~UI.'" !.tt:: ~: Col .. ,ltli NBIII II D I,II r I UlIIIII lUiH,11J1 llm Ot .. , .r .. r. ~ Nt •• ,II," {I i", 0 ... 11. M. h l • • ula '00 .. .. ! ~ n .. , ~ ~ n " .. i ~ ~ ~ ~ .. " • ... ••• J~" • 4-1 .. lI .... , ........ oN ' _.,.' __ ~ .. ' ••• ON-----+ . .. ' ....... QN FIG. I.-Relative percent ages of insects of various or de rs captur ed by Mi crOl1l/ct er is megalotis during the six sampling pe rio ds. The vertical bar on the l eft gives mean overall percentages of eac h insect order during the entire s tud y pe ri od. The ve rti ca l bar on the ri ght is ba se d on similar da ta for M icronyc ler;s liir s utu (Wil so n. 1971). The numbers of wings likely to be dropped probably vary a mong different orders a nd families of insects. For example, the win gs of small, delicate in sects (like many Diptera) may be cons umed, or may fall off at the instan t of capture, whereas this would rarely hap pen with Coleoptera. T he bia s introdu ced by wing loss cannot be quantified fro m our data and probably occurs in simila r data present ed in the litera tu re. We therefore believe it is best to restrict o ur discussi on to numbers of wings. Although not avoiding the bia.~, at least we can compare numbers of wings in this study wi th numbers re po rted in similar studies. Also, other biases mu.~t result from s pa cing co ll ecting pe riods at i nte.va ls of a month or lon ge r, du e to seasonal chan ges in weather, in lif e cycles of the bats a nd th eir prey , a nd in el eme nt s of the Aorn and Jauna on wh i ch the y depend . Idea ll y, fra gments s hou ld be co ll ected dail y. We al so realize that any i nsec t lar vae e ate n would lea ve no fragment record under the r oos t. About 10% of the 2,692 wings tabulated (Table 1) were selected randomly and measured to es timate body length (Fig. 2 ). Sizes and frequencies give but an imperfect im p r es.~ i o n of relative TABLE I.-M onthly dis tri b ution among or ders of 2,692 insect wings removed from two night roosts of Micronycteris mega lo tis at La Selua, Costa Rica. See text for details of tabulation. T;uron SCp( .- OcI. No v. IA-c .- J nl'l . I~ · Ft"ll. Ju n" Orthoptera 13 105 ZOO 210 63 21 Lepidoptera 17 25 27 35 9 6 H om optera 32 79 24 Z 21 Co l eopte ra 8 280 895 271 37 49 Odo nata 4 8 28 11 7 2 Dipte ra 10 56 55 11 Other orders 1 2 42 18 8 Totals 43 462 1.327 624 137 Downloaded from https://academic.oup.com/jmammal/article/61/2/327/903740 by guest on 09 March 2021 May 1980 Numbers of o Wings Measured Orthoptera Lepidoptera Homoptera Coleoptera Odonata Diptera 4 -10 GENERAL NOTES 329 Wing Size Classes in mm 11-20 21-30 31-4041-58 37 0 320 25 0 905 FIG. 2.-Length categories of wings of insects captured by Micronycteris megalotis during the period September 1973 through June 1974. dietary importance of various insect orders to the bats. Insects of equal length may vary greatly in mass (for example, a lO-mm cranefly and a lO-mm scarab beetle), and there may be significant differences in nutritional values among insects of equal mass but representing different orders. Coleoptera represented the most frequent items in the diet during the study period, ranging from 19 to 67% (Fig. 1). These were mostly small beetles of the family Scarabaeidae, although Cleridae and several unidentified families were also represented. No large beetles (>15 mm elytra length) were found (Fig. 2). Orthoptera were the se(:ond most frequent items among the insects represented in the diet. Grasshoppers (Acrididae), cockroaches (Blattidae), crickets (Gryllidae), and katydids (Tettigoniidae) were all common food items. Although a major item in all samples (ranging from 15% to 46%) relatively few orthopterans were taken in the late wet season. In the dry season, however, they represented nearly half the diet. Their actual contribution in tenus of biomass probably was greater than suggested by the numhcrs of wings found. No other insect order was represented significantly in all samples. Minimum frequencies for other orders ranged from 0.4 to 2.0%. Lepidoptera accounted for almost 40% of all insects consumed in the September-October sample, but were taken in relatively small numbers in other months. Moths represented were mainly noctuids, but included smaller numbers of Sphingidae, Sahlrniidae, Notodontidae, and Uraniidae. Remains of the butterfly families Satyridae and Nymphalidae were also found. The Homoptera, a significant prey item in June, followed the Lepidoptera in importance. These were mostly hoppers (Membracidae and Cicadellidae) plus a few cicadas (Cicadidae). Orders less well represented included the Diptera, which were taken mainly during the late wet season and the dry season, and the Odonata (mostly dragonfilies), which were represented in small numbers throughout the study period. The Hymenoptera (wing size range, 5-15 mm), Hemiptera (9-11 mm), Ephemeroptera (5-14 mm), Trichoptera 00-13 mm), Mecoptera (11-13 mm), and Neuroptera (no intact wings found) were poorly represented in the samples. Micronycteris megalotis is a slow-flying, highly maneuverable, foliage-gleaning bat capable of hovering (observed in this study). Although their food includes flying insects (moths and beetles), other noch!rnal prey (Homoptera and Orthoptera, except grasshoppers) are usually found perched on vegetation, ratherthan in flight. The flies, dragonflies, and grasshoppers eaten are mostly diurnal. The nocturnal groups accounted for most of the remains recovered at the M. megalotis roosts. Most orthopterans are noisy, especially when calling, and beetles are noisy in Downloaded from https://academic.oup.com/jmammal/article/61/2/327/903740 by guest on 09 March 2021 330 JOURNAL OF MAMMALOGY Vol. 61, No.2 Right. The hats may home in on the sounds produced by these insects, which together constituted over 70% of their diet. Unfortunately, no seasonal insect abundance data are available for La Selva. Data collected by light-trapping in Panama suggest that relative abundance among insect groups can cycle in the course of a year (Smythe, 1974). We suspect that M. megaiotis is partly opportunistic, and takes advantage of seasonally abundant insect populations. However, if M. megalotis and the similar, but larger, M. hirsuta were strictly opportunistic, one might expect that proportions of insect orders in their diet would be similar, even though the smaller species might select smaller insects. Based on data presented herein and from wilson (1971) we note that this is not the case (Fig. 1). Furthermore, M. hirsuta apparently consumes fruit during the dry season; no remains of fruit were recovered under M. megaiotis roosts, even though frugivorous habits have been reported for this species (Gardner, 1977). In its preference for beetles, M. megaiotis seems to differ from most other foliage-gleaning bats (see Gardner, 1977; LaVal and LaVal, in press). Unlike M. hir.mfa, three species of Nycferis, and Macrotus californicus (see Wilson, 1971; LaVal and LaVal, in press; Ross, 1967), M."megalotis seems to prefer small, hard-bodied insects (small beetles) as opposed to large, soft~bodied insects. These larger insects (including orthopterans, homopterans, and lepidopterans) are probably taken by M. megalotis whenever more convenient, perhaps when populations are at seasonal highs or when populations of preferred insect prey (beetles) are at seasonal lows. The food habits of M. megalotis may also reflect competition with some or all of the other 15 species ofphyllostomatine bats with which it occurs sympatrically at La Selva. We thank P. A. Opler and T. L. Zinn, who assisted us in identifying the insects; R. Swain and S. Kleinfeldt, who aided us by collecting insects at the night roost in their house; J. Campabadal and the stafl of the Organization for Tropical Studies for logistical snpport; and M. B. Fenton, who contributed numerous helpful suggestions on an earlier version of this report. Financial support was provided by NSF Grant GB 25592 to H. S. Fitch. LITERATURE CITED FENTON, M. B. 1975. Observations on the biology of some Rhodesian bats, including a key to the Chiroptera of Rhodesia. Contrib. Life Sci., Royal Ontario Mus., 104:1-27. FENTON, M. B., N. G. H. BOYLE, T. M. HARRISON, AND O. J. OXLEY. 1977. Activity patterns, habitat use, and prey selection by some African inscctivorous bats. Biotropica, 9:73-85. FLEMING, T. H. 1974. The population ecology of two species of Costa Rican heteromyid rodents. Ecology, 55:493-510. GARDNER, A. L. 1977. Feeding habits. Pp. 293-350, in Biology of bats of the New World family Phyllostomatidae. Part II (R.]. Baker, J. K. Jones,Jr., and D. C. Carter, eds.). Spec. Publ. Mus., Texas Tech Univ., 13:1364. KUNZ, T. H. 1974. Feeding ecology of a temperate insectivorous bat (Myotis velifer). Ecology, 55:693-711. LAVAL, R. K., AND H. S. FITCH. 1977. Structure, movements, and reproduction in three Costa Rican bat communities. Oecas. Papers Mus. Nat. Hist., Univ. Kansas, 69:1-28. LAVAL, R. K., AND M. L. LAVAL. - In press. Prey selection by the slit-faced bat Nycteris thebaica (Chiroptera: Nycteridae) in Natal, South Africa. Biotropica. ORIANS, G. H. 1969. The number of bird species in some tropical forests. Ecology, 50: 783-80l. Ross, A. 1967. Ecological aspects of the food habits of insectivorous bats. Proc. Western Found. Vert. Zool., 1:204-263. SMYTHE, N. D. 1974. Insect sampling. Pp. 43115, in 1973 environmental monitoring and baseline data (R. W. Rubinoff, ed.). Smithsonian Inst. Environ. Sci. Program, Trop. Studies, 465 pp. WHITAKER, J. 0., JR., AND H. BLACK. 1976. Food habits of cave bats from Zambia, Africa. J. Mamm., 57:199-204. WILSON, D. E. 1971. Food habits of Micronycteris hirsuta (Chiroptera: Phyllostomidae). Mammalia, 35:107-110. RICHARD K. LAVAL AND MARGARET L. LAVAL, Missouri Department of Conservation, Fish and Wildlife Research Center, 1110 College Ave., Columbia, MO 65201. Submitted 3 January 1979. Accepted 31 July 1979. }. Mamm., 6\(2):327....330. 1980 Downloaded from https://academic.oup.com/jmammal/article/61/2/327/903740 by guest on 09 March 2021