Preferencje help
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 10

Liczba wyników na stronie
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników

Wyniki wyszukiwania

help Sortuj według:

help Ogranicz wyniki do:
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
We examined data sets on dietary composition of a rich (15 species) assemblage of animal-eating Neotropical leaf-nosed bats (Phyllostomidae: Phyllostominae) that occur syntopically on Barro Colorado Island, Panama. Our aim was to test previously postulated trophic structure of phyllostomines in the light of alternative analytical techniques and new data. The trophic structure of this assemblage, according to new results from Correspondence Analysis, has two main trends of variation: a gradient of increased carnivory (axis 1) and a gradient involving plant and arthropod consumption (axis 2). This rejects previous hypotheses of this guild in which the structure was described as a complex of many independent discrete resources. Although all data sets agree that coleopterans as a group are an important food item for most species, Phyllostominae bats are not typically durophageous; i.e., they lack cranial and dental adaptations for rapid processing of hard-shelled arthropods as found in other bat families. Furthermore, insectivory varies inversely with body size, and is gradually replaced by carnivory in association with increasing mass and limited dental modifications. Together with CA results, this suggests that carnivory is an extreme of animalivory rather than a qualitatively distinct feeding habit among Phyllostominae bats. This conclusion fits biomechanical data that indicate that carnivorous bats are bigger and only modestly modified versions of soft-insect specialists.
We analysed the distribution and relative abundance of Myotis daubentonii in the lowlands and uplands around the Lahn river near the city of Giessen (Hessen, Central Germany). We assumed a positive correlation between distribution and relative abundance of the trawling M. daubentonii with the amount of water surface in our study area. We further expected an unequal distribution of male and female M. daubentonii especially during the energy demanding pregnancy and lactation period of females. Daubenton's bats were found at 75% of the 64 ponds and lakes we surveyed by standardized nightly spotlight counts. The number of Daubenton's bats correlated positively with the area of the water surface and negatively with the distance to the nursery colonies. Nursery colonies were located with radio-tracking and existed predominantly in the lowlands close to the Lahn river. Mean flight distance between nursery colonies and foraging areas was 2.3 km (mean ± 1.4 km, range: 0.6–6.3 km). Sex ratio was determined at three sites studied in detail from 1992–2003 by mist-netting along regular used flight paths (n = 1,847 caught individuals). The number of female per male M. daubentonii was unequal and differed significantly between the three sites. In the lowland we found one site clearly dominated by females (median = 4.3 females per male, percentages of females 79.3%, n = 169 individuals) and a second site with an almost balanced sex ratio (median = 1.1 females per male, percentages of females 50.3%, n = 939 individuals). At the third site in the uplands males outnumbered females (median = 0.2 females per male, percentages of females 13.5%, n = 739 individuals). The percentages of females remained largely constant from spring to mid summer and changed at the beginning of September. The study revealed that a detailed knowledge of the spatial distribution of gender specific roost sites and key foraging habitats is necessary for the establishment of meaningful monitoring and conservation measures for bats.
We investigated spatial use and foraging behaviour of the nectarivorous African long-tongued bat, Megaloglossus woermanni (Chiroptera: Pteropodidae), in the Lama Forest Reserve, southern Benin, West Africa. We monitored movement and activity patterns of two males and two females that were fitted with position-sensitive radio transmitters for five to nine nights within a three-month study period. The study site comprised the central patch of relatively undisturbed forest (‘Noyau Central’), and a mosaic of orchards, agroforestry plantations, and degraded forests surrounding the central patch. Spatial use of M. woermanni was characterized by small home ranges and high site-fidelity. Mean home range sizes (minimum convex polygon) were larger in females (139.0 and 146.8 ha) than in males (99.8 and 102.9 ha). Throughout the study period, long-tongued bats were frequently observed visiting flowers of cultivated bananas. The mean foraging areas (95% density kernel) of females (39.0 and 109.4 ha) were much larger than in males (12.3 and 14.1 ha). Difference in core areas (50% density kernel) between the sexes was less marked (both females: 6.8 ha, males: 2.7 and 2.9 hectares). Core areas constituted only a small part of home ranges (2.6-4.9%). Large segments of the home ranges were only used for commuting flights between discrete resource patches. Our study provides, for the first time, information on home ranges and foraging behaviour of the sole obligate nectar-drinking bat in Africa.
The Neotropical fringe-lipped bat, Trachops cirrhosus, is a generalist predator that hunts frogs and insects by homing in on their mating calls. Although research has examined cognition and prey preferences of bats in captivity, little is known of the foraging or roosting behaviour of this species in the wild. We radio tracked six T. cirrhosus individuals on Barro Colorado Island, Panamá. Bat day roosts were all in hollow cashew trees, Anacardium excelsum, in mixed sex groups of three to five T. cirrhosus individuals, with frequent roost switching. Radio tracked individuals flew an average of 218 ± 227 m from their day roosts to 12.0 ± 10.17 ha foraging areas (50% utilization distribution [UD] kernels = areas where bats spent 50% of their time as estimated from a probability distribution). These 50% UD kernels were less than 10% of their average total range use, but larger than previously reported for T. cirrhosus. Radio tracked individuals overlapped in 50% UD kernel foraging areas by only 2.1 ± 5.9 % on average. Foraging behaviour consisted predominantly of short sally flights of less than one minute, indicating bats were likely perch hunting. Bats were more frequently in flight, and had longer flight durations, at the beginning of the night and just before dawn than throughout the rest of the night. These data provide insight into the foraging behaviour of T. cirrhosus in the wild, that is a species fast becoming a model system of cognition in captivity.
To assess the influence of habitat fragmentation on small bats, we determined home range size and mobility of the frugivorousArtibeus watsoni Thomas, 1901 and the gleaning insectivorousMicronycteris microtis Miller, 1898 by radiotracking on different-sized islands (2.7–17 ha) in Lake Gatún, Panamá. The two species differed in their response to fragmentation. Home range size was highly variable in the five trackedA. watsoni, ranging from 1.8 to 17.9 ha with a mean of about 9 ha. Some individuals flew regularly between islands and/or the mainland, thereby traversing up to 180 m of open water. In comparison, home ranges of threeM. microtis were with about 3.8 ha only half as large. All ofM. microtis exhibited sedentary foraging behaviour and did not cross open water, suggesting that they might persist at least on some of the islands as resident populations. Our findings are consistent with radiotracking data from a previous study and indicate that small habitat patches are still used by small bats, provided the degree of isolation is low and that sufficient resources and larger habitat patches exist in close vicinity, potentially acting as additional feeding grounds and source populations.
The decision on when to emerge from the safety of a roost and forage for prey is thought to be a result of the trade off between peak insect abundance and predation pressure for bats. In this study we show that the velvety free-tailed bat Molossus molossus emerges just after sunset and just before sunrise for very short foraging bouts (average 82.2 min foraging per night). Contrary to previous studies, bats remain inactive in their roost between activity patterns. Activity was measured over two complete lunar cycles and there was no indication that phase of the moon had an influence on emergence time or the numbers of bats that emerged from the roost. This data suggests that M. molossus represents an example of an aerial hawking bat whose foraging behaviour is in fact adapted to the compromise between the need to exploit highest prey availability and the need to avoid predation.
Although recognized as highly diverse, the bat fauna of the Amazon basin has been only patchily sampled. This paper combines data from five short surveys conducted between 1998 and 2001 in Jaú National Park, 220 km east of Manaus, central Amazônia. We used mistnets, recordings of echolocation calls and roost visits to provide the first bat inventory for this area. A total of 53 bat species in 33 genera and five families were documented, including several species that are regarded as rare, in particular Saccopteryx gymnura, Vampyriscus brocki, Molossops neglectus, and Promops centralis. The Chao 1 index indicates that sampling is about 72% complete, suggesting that around 73 bat species might co-exist in Jaú. We compare the composition of Jaú's bat fauna to those of other sites in Amazônia and interpret the resulting patterns of diversity. Data on reproduction are given for 14 species.
Noack's round-leaf bat Hipposideros cf. ruber is widely distributed in sub-Saharan Africa. Here, we present some aspects of its ecology from two caves in central Ghana. Our main objective was to assess the nightly and annual flight activity and to examine the influences of ambient temperature on flight activity. We tested the hypothesis that flight activity of the species is concentrated at certain periods of the night and the year using mist-netting data from 2,712 captured bats. We found no evidence for annual fluctuations in flight activity, probably due to no distinct seasonal limitation of food resources, no migration, and the lack of extreme environmental conditions in the study area. Our hypothesis of concentrated nightly flight activity was confirmed for one cave but not for the other. Flight activity was concentrated early in the night (20:00, 21:00 and 22:00 hours) at one cave, possibly to take advantage of locally available early active prey insects, while it was uniformly distributed throughout the night at the other. Lastly, we found a reduction in the flight activity of H. cf. ruber when there was a distinct drop in temperature over the night. We therefore suggest the reduction in flight activity may result from the direct effects of temperature on prey abundance as the bats responded by reducing activity to avoid excessive prey search costs.
Thirteen individuals of Noack's round-leaf bat, Hipposideros aff. ruber, were radio-tracked for 38 nights in an agricultural landscape in Kwamang, Ashanti Region, Ghana. Local convex hulls were used to estimate home range sizes of the bats. Based on 1,192 fixes, the mean (± SD) home range size was 36 ha ± 35 ha. Individual home range size ranged from six to 95 ha and frequently overlapped among individuals. The foraging area covered 50% of the home range while the core area formed 2%. The mean maximum foraging distance was 1.1 km, with individual distances up to 2.6 km, suggesting Hipposideros aff. ruber is capable of covering relatively long distances. Male bats returned to the cave more often than females during the night. Although the cave was the main roost, each bat also had individual night roosts on trees.
Pierwsza strona wyników Pięć stron wyników wstecz Poprzednia strona wyników Strona / 1 Następna strona wyników Pięć stron wyników wprzód Ostatnia strona wyników
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.