Maarten J. Vonhof

Roosting Behavior and Roost-Site Preferences of Forest-Dwelling California Bats (Myotis californicus)

We followed nine radiotagged female California bats ( Myotis californicus ) to 19 roosts in trees at two study sites in southcentral British Columbia. Bats regularly switched roosts and the number of bats emerging from known roosts fluctuated widely. Logistic-regression analysis showed that reproductively active females preferred trees further away from other trees of the same height or greater, and closer to neighboring trees, relative to available trees in the immediate vicinity of the roost. Diameter at breast height and distance to the nearest tree of the same or greater height explained significant proportions of the variation between roost and available trees found in other areas of the same forest stand. Roost trees had significantly larger diameters and were further away from trees of the same or greater height. Percentage of canopy closure also explained a significant proportion of the variation between roost and available trees, such that roost trees were situated in areas with lower canopy closure than available trees in other areas of the same stand. Roost and available trees were classified correctly >70% of the time based on the above tree characteristics. However, roost trees were only correctly classified 39% of the time in the analysis of site characteristics. Our results, combined with those from other recent studies, lead to the general hypothesis that forest-roosting bats require a number of large dead trees of specific species, in specific stages of decay, and that project above the canopy in relatively open areas. For management and conservation reasons, there should be a strong incentive to evaluate this hypothesis for a variety of species in a variety of locations to test its generality.

Use of tree stumps as roosts by the western long-eared bat

We report for the first time widespread use of loose bark on stumps in clearcuts as roosting sites by bats. We first discovered stump-roosting behaviour during the summer of 1993 when a radiotagged female western long-eared bat (Myotis evotis) roosted beneath loose bark on 4 separate stumps. During the summer of 1994 we searched for stump roosts in 11 south-facing clearcuts in the West Arm Demonstration Forest near Nelson, British Columbia. Nineteen roosts in 17 different stumps were located in 3 of the 11 clearcuts searched. Males and females accounted for 10 and 9 of the 19 roosts. Within clearcuts, bats selected large-diameter stumps, and tended to roost in southwest facing cavities. Temperatures of roost cavities were intermediate between those within randomly selected cavities and ambient temperatures. Temperatures within randomly selected cavities were significantly warmer than ambient temperatures, while those within roosts were not. Cavity temperature was related negatively to stump diameter, and cavities on the south side of stumps were relatively warm. We conclude that bats chose to roost in clearcuts to gain thermal benefits through increased exposure to sunlight and reflective heat, but within these clearcuts chose stumps that provided relatively cooler and more stable temperatures, presumably to avoid heat stress. Bats selected clearcuts with high proportions of uncluttered stumps, and stumps in clearcuts used by bats provided deeper cavities relatively far away from neighboring shrubs. Bats roosting in clearcuts may be subject to a trade-off between increased energetic savings and increased predation risk.

Time-Expansion and Zero-Crossing Period Meter Systems Present Significantly Different views of Echolocation Calls of Bats

Abstract We compared 2 bat detecting systems that use condenser microphones, 1 that performed computer analysis (Anabat6) of the output of a zero-crossing period meter (Anabat system) and the other that performed computer analysis (Canary 1.2) of the output of slowed-down (= time-expanded) recordings (Racal system). The 2 systems provided significantly different pictures of both numbers and characteristics (highest frequency, lowest frequency, and duration) of echolocation calls, whether recorded from free-flying bats in the field or from a stationary bat in the laboratory. Although the AnabatII detector was slightly more sensitive than the QMC S200 detector, the Racal system detected more echolocation calls than the Anabat system; the 19-dB difference in sensitivity was associated with a zero-crossing period meter in the Anabat system. Results suggest 2 recommendations. First, that analysis using zero-crossing period meters should not be used to describe echolocation behavior or calls of bats. Second, that studies of activity and use of habitat based on analysis using zero-crossing period meters should involve calibration against more sensitive bat-detecting systems.

No Evidence for Acoustic Mate-Guarding in Duetting Buff-Breasted Wrens (Thryothorus Leucotis)

There are few empirical tests of the acoustic mate-guarding hypothesis for the function of duetting in birds. This hypothesis states that when females are fertile, males initiate many songs or answer most of their mates’ solo songs to form duets and repel rival males seeking extra-pair copulations. We tested the hypothesis by comparing song initiation and answer rates of males and females in socially monogamous buff-breasted wrens (Throthorus leucotis) during pre-fertile and fertile periods. During pre-fertile periods, males often sang for short periods before being answered by their mates, yet first duets were formed earlier relative to dawn and more duets were given during the dawn chorus on pre-fertile than fertile mornings. Males initiated more songs during pre-fertile than fertile periods, whereas there was no difference between stages in female song initiation rates. The proportion of songs answered by individuals of both sexes did not differ between breeding stages. Other mate-guarding behaviours, such as frequent copulation and maintaining close proximity to mates when fertile, did not appear to be important in this species, as no copulations were observed and there was no difference in the time pairs spent in close proximity when females were fertile or not. Parentage analysis revealed that only 3% of 31 broods had young that were likely the result of extra-pair paternity. These findings do not support the acoustic mate-guarding hypothesis, and suggest that the low rate of extra-pair paternity in buff-breasted wrens was maintained without the use of acoustic or traditional paternity guards.

Roost availability and population size of Thyroptera tricolor , a leaf-roosting bat, in north-eastern Costa Rica

Estimates of roosting habitat availability and population size using unbiased sampling regimes are completely lacking for any bat species. The use of conspicuous and accessible roosts in the developing, rolled leaves of Heliconia and Calathea plants by Thyroptera tricolor (Spixs disc-winged bat) provided an ideal opportunity to address this need. To assess roost availability and population size, the number of occupied and unoccupied leaves and bats in known areas in an area of lowland rain forest in north-eastern Costa Rica were quantified in 1998-99. A high density of leaves was available on any given day (mean: 43 leaves ha -1 ), but the density of roost leaves was low (mean: 2.5 leaves ha -1 ), corresponding with a low occupancy rate of 5.7 or 12% based on different methods of estimation. Developing leaves were available for 8-16 h in the preferred size range of leaves used by T. tricolor, and a maximum of 28-60 h, depending on the plant species. Using closed-population mark-recapture models, the 5.69-ha study area supported 261 individuals over a 4-mo period in 1998, corresponding to a density of 43 bats ha -1 . These results have important implications for the results of studies on bat community structure and rarity, and for the behaviour and ecology of T. tricolor.

Ectoparasitic insects of bats in British Columbia, Canada

One species of parasitic bug (Hemiptera: Cimicidae), 3 species of fleas (Siphonaptera: Ischnopsyllidae), and 2 species of parasitic flies (Diptera: Nycteribiidae) were collected from 9 species of bats (Chiroptera: Vespertilionidae) in southern interior and northeastern British Columbia, Canada. Female bats that return daily to maternity roosts were more frequently infested with both cimicids and ischnopsyllids than were male bats. Some differences in ectoparasite infestation can be attributed to differences in roosting behavior of the host. New national records for 2 parasite species, and 8 new host records are established for Canada.

Bats from Fazenda Intervales, Southeastern Brazil: species account and comparison between different sampling methods

Assessing the composition of an areas bat fauna is typically accomplished by using captures or by monitoring echolocation calls with bat detectors. The two methods may not provide the same data regarding species composition. Mist nets and harp traps may be biased towards sampling low flying species, and bat detectors biased towards detecting high intensity echolocators. A comparison of the bat fauna of Fazenda Intervales, southeastern Brazil, as revealed by mist nets and harp trap captures, checking roosts and by monitoring echolocation calls of flying bats illustrates this point. A total of 17 species of bats was sampled. Fourteen bat species were captured and the echolocation calls of 12 species were recorded, three of them not revealed by mist nets or harp traps. The different sampling methods provided different pictures of the bat fauna. Phyllostomid bats dominated the catches in mist nets, but in the field their echolocation calls were never detected. No single sampling approach provided a complete assessment of the bat fauna in the study area. In general, bats producing low intensity echolocation calls, such as phyllostomids, are more easily assessed by netting, and bats producing high intensity echolocation calls are better surveyed by bat detectors. The results demonstrate that a combined and varied approach to sampling is required for a complete assessment of the bat fauna of an area.

The diet of bats from Southeastern Brazil: the relation to echolocation and foraging behaviour

In this study the incidence of moths and beetles was examined from feces samples of bats that use different foraging behaviors. Twenty sites around the Fazenda Intervales, a Field Research Station located in Sao Paulo State, in southeastern Brazil were sampled. Feces were collected from bats caught in mist nets, Turtle Traps or hand nets and, in one case, from beneath a roost. Feces samples were taken from six species of bats: Micronycteris megalotis (Gray, 1842), Mimon bennettii (Gray, 1838), Furipterus horrens (F. Cuvier, 1828), Myotis riparius Handley, 1960, Myotis ruber (E. Geoffroy, 1806) and Histiotus velalus (I. Geoffroy, 1824). To record and describe the frequencies dominating bat echolocation calls, an Anabat II bat detector coupled with an Anabat ZCA interfaces and DOS laptop computers were used. The data show that Furipterus horrens feeds extensively on moths, as predicted from the features of its echolocation calls. Gleaning bats, whose echolocation calls are much less conspicuous to moths take a wide range of insect (and other) prey.

Nutrient Preferences of Brazilian Hummingbirds

Abstract The Stripe-tailed Hummingbird (Eupherusa eximia) prefers nectar that is highly supplemented in both vitamins and minerals, when offered the choice of no, low, or high supplemented nectar. We tested the responses of hummingbirds in southern Brazil to four solutions: nectar, nectar supplemented with vitamins, nectar supplemented with minerals, and water with both vitamins and minerals added. Hummingbirds spent less time at and made fewer visits to the supplemented water than to the different nectar solutions, suggesting that nutrients alone are not enough to attract birds. One of eight species, the Violet-capped Woodnymph (Thalurania glaucopis), visited the mineral supplemented nectar more often than both nectars and one unidentified hermit species (Phaethornis sp.) visited the mineral treatment more than straight nectar. The Black-throated Mango (Anthracothorax nigricollis) made more visits to the vitamin supplemented nectar than to mineral-rich nectar whereas the Glittering-bellied Emerald (Chlorostilbon aureoventris) avoided the vitamin treatment, preferring straight nectar. A general pattern of preference was not found among species.