Harem social organization in cave roosting artibeus jamaicensis chiroptera phyllostomidae

The social organization of Artibeus jamaicensis was examined in Aguas Buenas Cave, Puerto Rico, by sampling roosting clusters of bats during the spring reproductive period. Most clusters consisted of 2-14 pregnant or lactating females (and their young) and a single adult male. This suggests a harem type of social organization. Two types of non-harem groups represented by nonreproductive females or sexually mature males supports this conclusion. Although our observations do not permit distinction between alternative explanations for harem formation, they do indicate that successful harem aquisition and maintenance is age or size related. Older and heavier males had larger harems than younger or smaller harem males. The occurrence of harem groups in tree hollows (Morrison 1979) and in caves (this study) suggests that environmental factors promoting harem social organization in A. jaamaicensis can vary between populations. BATS EXHIBIT A DIVERSITY OF social and mating systems (Bradbury 1977a), including promiscuity (e.g., Myotis lucifugus, Thomas et al. 1979), monogamy (e.g., V1ampyrum spectrum, Vehrencamp et al. 1977), female-defense polygyny (e.g., Phyllostomas hastatus, McCracken and Bradbury 1977, 1981), resource-defense polygyny (e.g., Artibeus jamaicensis, Morrison 1979; Morrison and Morrison 1981), and leks (e.g., Hypsignathus monstrosus, Bradbury 1977b). Certain components of bat social organization such as group size, age structure, sex ratio, and population density can vary considerably among populations (Bradbury 1977a, Bradbury and Vehrencamp 1976), particularly where there is variation in habitat conditions. Knowledge of intraspeciflc variation in social organization is necessary to fully understand how environmental and demographic factors influence the evolution of social systems (Eisenberg 1981). The phyllostomid bat Artibeus jamaicensis is well suited for evaluating variation in social and mating organization. This species has a widespread distribution, including several insular forms (e.g., Baker and Genoways 1978), and it is one of the most abundant bats occurring in the Neotropics. Roosting sites include tree hollows (Morrison 1979, Morrison and Morrison 1981), foliage (Goodwin and Greenhall 1961; Jimbo and Schwassman 1967; Foster and Timm 1976; Morrison 1978a, 1979), and caves (Dalquest 1953, Tuttle 1968, Goodwin 1970, Thomas 1974, Lemke 1978). With the exception of Morrison's (1979) study, little is known of group composition for roosting A. jamaicensis in these situations. Morrison described a resource-defense polygyny system for this species on Barro Colorado Island, Panama, and in Chamela, Mexico. Males maintained harems by defending tree hollows used by groups of females as day roosts. He suggested that this type of mating system was feasible only in habitats where a limited number of tree hollows were available as day roosts, and that the cost to males of defending "less confined" roosts such as caves and foliage might be prohibitive. The purpose of this study was to determine the social structure of A. jamaicensis roosting in a cave environment. MATERIALS AND METHODS We sampled the composition and distribution of day roosting clusters of A. jamaicensis during the spring reproductive period in Aguas Buenas Cave, Puerto Rico (6606'30"W, 18014'01"N) from 5 May to 16 May 1981. We limited our survey of bats to the upper, drier portion of the cave system. Details of the geology, ecology, and mycology of this cave are given elsewhere (Peck 1974; Beck et al. 1976; Carvajal-Zamora 1977a, b, c). Clusters of A. jamaicensis were found in solution cavities on the ceiling usually well away from entrances (Fig. 1). Those cavities occupied by A. jamaiciensis were generally 4-15 m above the cave floor and were usually dome-like in shape, approximately 0.5-1 m in diameter by 1-2 m deep. If no loud disturbances were made, roosting bats allowed us to walk directly beneath them. Clusters of Artibeus were captured using a device similar to that described by McCracken and Bradbury (1981). This consisted of a cylindrical, plastic trash bucket (32 X 36 cm) with the bottom removed. A 45 cm deep hardware cloth basket (2.5 mm mesh), with a 4 cm hole in the bottom, was attached beneath the plastic bucket. The entire device was attached with the open end of the bucket at the tip of a 3.5 m pole. Clusters of A. jamaicensis were collected by quickly placing the open end of the ' Present address: Department of Zoology, University of Rhode Island, Kingston, Rhode Island 02881, U.S.A. 2 Present address: Illinois Natural History Survey, 607 E. Peabody Drive, Champaign, Illinois 61820, U.S.A. BIOTROPICA 15(2): 133-138 1983 133 This content downloaded from 157.55. 39.45 on Fri, 02 Sep 2016 05:41:32 UTC All use subject to http://about.jstor. org/terms bucket into occupied solution cavities, thus obstructing the bats' route of exit. A second pole inserted through the hole at the bottom of the container was carefully maneuvered so that bats dinging to the sides of the cavity were dislodged. For each captured individual, we recorded sex, age class, reproductive condition, body mass, forearm length, canine tooth wear class, and for males, testes length and canine length. We recognized three age classes: juveniles (bats attached to a lactating female or with unfused phalangeal epiphyses), subadults (bats with fused epiphyses but without adult pelage), and adults (bats with fused epiphyses and adult pelage). Reproductive conditions recorded were extraor intra-abdominal testes for males and lactating, pregnant, or non-breeding for females. All linear measurements were taken with dial calipers, and body mass was measured with a Pesola spring scale. Tooth wear classes were adopted from Twente (1955). Briefly, completely worn canines were given a score of six and sharply pointed, unworn canines were scored as one. Bats from each cluster were marked with a unique set of colored plastic wing bands. Males were banded on the right forearm and females on the left. All bats were released immediately after being examined, usually no more than two hours after capture. The location of solution cavities in which dusters were captured was marked with a small flag on the cave floor. The presence or absence of bats in each of the censused solution cavities was noted on subsequent visits to the cave. To estimate the abundance of potential roost sites, two of us independently walked through the cave where A. jamaicensis was known to roost. Both of us recorded the number of occupied solution cavities as well as the number of unoccupied cavities showing signs of use. Solution cavities used by roosting bats had conspicuous, dark excrement stains on the sides of the dome interior. We characterized air temperature in occupied and unoccupied solution cavities by placing a thermistor probe attached to the end of a long wooden pole near the domes of cavities. The thermistor was interfaced with a Yellow Springs, Model 44, Telethermometer, which provided immediate temperature readings. Air temperature also was recorded at various heights and locations throughout the cave. FIGURE 1. Small harem group of Artibeus jamaicensis occupying a solution cavity in Aguas Buenas Cave, Puerto Rico. 134 Kunz, August, and Burnett This content downloaded from 157.55. 39.45 on Fri, 02 Sep 2016 05:41:32 UTC All use subject to http://about.jstor. org/terms