Territorial and pair behaviour of the African false vampire bat, Cardioderma cor (Chiroptera: Megadermatidae), in coastal Kenya

Curdioderma hangs from habitual perches to wait for mainly terrestrial prey. Their broad wings provide the lift at low speeds necessary to capture such prey from the ground. Male-female pairs were found in the long dry season, a period when reduced insect availability led to lower body weights and males used song to delineate their feeding territories. Males moved between perches more frequently during the first half-hour of nightly singing. An enlargement of foraging area was associated with earlier singing, as well as an increase in song rate, movement between perches and pair contact-vocalizations. Females are larger than males and the sex ratio favoured the latter. There was evidence of long-term territories and breeding throughout the year. These results are discussed in relation to pair-bonding and environmental seasonality.     

Common principle of guidance by echolocation and vision

1. Using echolocation, bats move as gracefully as birds through the cluttered environment, suggesting common principles of optic and acoustic guidance. We tested the idea by analysing braking control of bats (Macroderma gigas) flying through a narrow aperture with eyes covered and uncovered. 2. Though braking control would seem to require rapid detection of distance and velocity and computation of deceleration, simpler control is possible using the tau function of any sensory variable S that is a power function of distance to aperture. Tau function of S is tau (S) = S/S (the dot means time derivative). Controlled braking is achievable by keeping tau (S) constant. 3. Previous experiments indicated the tau (S) constant procedure is followed by humans and birds in visually controlling braking. Analysis of the bats' flight trajectories indicated they too followed the braking procedure using echolocation. 4. The tau function of echo-delay or of echo-intensity or of angle subtended by directions of echoes from two points on the approach surface could be used to control braking. Aperture size was modulated during flight on some trials in an attempt to test between these possibilities, but the results were inconclusive.     

Passive sound localization of prey by the pallid bat (Antrozous p. pallidus)

Summary The pallid bat (Antrozous p. pallidus) uses passive sound localization to capture terrestrial prey. This study of captive pallid bats examined the roles of echolocation and passive sound localization in prey capture, and focused on their spectral requirements for accurate passive sound localization.Crickets were used as prey throughout these studies. All tests were conducted in dim, red light in an effort to preclude the use of vision. Hunting performance did not differ significantly in red light and total darkness, nor did it differ when visual contrast between the terrestrial prey and the substrate was varied, demonstrating that the bats did not use vision to locate prey.Our bats apparently used echolocation for general orientation, but not to locate prey. They did not increase their pulse emission rate prior to prey capture, suggesting that they were not actively scanning prey. Instead, they required prey-generated sounds for localization. The bats attended to the sound of walking crickets for localization, and also attacked small, inanimate objects dragged across the floor. Stationary and/or anesthetized crickets were ignored, as were crickets walking on substrates that greatly attenuated walking sounds. Cricket communication sounds were not used in prey localization; the bats never captured stationary, calling crickets.The accuracy of their passive sound localization was tested with an open-loop passive sound localization task that required them to land upon an anesthetized cricket tossed on the floor. The impact of a cricket produced a single 10–20 ms duration sound, yet with this information, the bats were able to land within 7.6 cm of the cricket from a maximum distance of 4.9 m. This performance suggests a sound localization accuracy of approximately ±1° in the horizontal and vertical dimensions of auditory space. The lower frequency limit for accurate sound localization was between 3–8 kHz. A physiological survey of frequency representation in the pallid bat inferior colliculus suggests that this lower frequency limit is around 5 kHz.     

The role of the forelimb in prey capture in the Late Triassic reptile Megalancosaurus (Diapsida,Drepanosauromorpha)

The pectoral girdle and forelimb of the Late Triassic drepanosauromorph reptile Megalancosaurus are redescribed and their function reinterpreted. The whole skeleton of this diapsid is highly specialised for arboreal life, and also the peculiarities of the shoulder girdle and forelimb were interpreted as adaptations for a limb-based locomotion using gap-bridging to move from one support to another, as in chameleons. Re-examination of the pectoral girdle and forelimb revealed the presence of clavicles fused into a furcula-like structure, a saddle-shaped glenoid and a tight connection between the radius and ulna that strengthened the forearm but hindered pronation and supination movements at that joint. The new information plus a reconstruction of the pectoral and forelimb musculature suggests that the forelimb was also specialised for grasping and raking in addition to climbing and thus prey capture may have been an important function for the forelimb. The new functional interpretation fits well with the overall body architecture of Megalancosaurus’ skeleton, suggesting that this reptile was an ambush predator that may have assumed a stable tripodal position, secured by the hooked tail and hind limbs, freeing its forelimbs to catch prey by sudden extension of the arm and firm grasping with the pincer-like digits.     

The role of stimulus movement patterns in the prey catching behavior ofHydromantes genei (Amphibia,Plethodontidae)

Summary The prey catching responses of the Italian salamanderHydromantes genei (Schlegel) were studied both with respect to continuous stimulus movement and to stepwise stimulus movement. The stimulus consisted of a black square measuring 4×4 mm. The responses to both continuous and stepwise stimulus movement were measured at 3 different basic velocities (0.5, 1.25, and 3.125 cm/s), and to stepwise stimulus movement at 6 different step frequencies (0.25, 0.5, 1, 2, 4, 8 steps/s). The experiments showed that within the measured step frequency range, frequencies of 1 and/or 2 steps/s have proved to be the most efficient in eliciting prey catching behavior. The efficiency of both stepwise and continuous stimulus movement increases with an increase of the basic velocity, but the efficiency ratios of stepwise and continuous stimulus movement have an inverse relationship to each other: at low basic velocities, where continuous stimulus movement is less effective, stepwise stimulus movement of the same basic velocity is considerably more effective; at high basic velocities, where continuous stimulus movement is rather effective, the stepwise stimulus movement of the same basic velocity is either not significantly different or proves to be less effective.     

The use of echolocation by the wandering shrew (Sorex vagrans)

Six wandering shrews (Sorex vagrans) were trained to echolocate the position of a platform and drop to it. They preferentially directed their ultrasonic emissions at the platform. With their ears plugged, they were unable to locate it above chance levels even though they increased their emission rate. Shrews with hollow tubes in their ears performed as effectively as controls. Echolocating shrews, trained on an elevated Y-maze, detected a 15×15-cm flat metal barrier to a distance of 65 cm. The minimum detectable barrier at 20 cm was 3·5×3·5 cm. They detected a target with a 4×4-cm hole to 30 cm. Their dependence on echolocation was inversely related to familiarity with an area. Audition was important for the location of suitable cover in strange areas. The adaptive significance of echolocation to the wandering shrew is discussed.     

Profitability, encounter rates, and prey choice of African lions

The prey preferences of African lions (Panthera leo) in SerengetiNational Park, Tanzania, were examined in three ways. First,lion encounter rates with prey types were measured and comparedwith a random sample of the prey population. Lions encounteredmore wart hogs (Phacochoerus aethiopicus), Grant's gazelles(Gazella granti), wildebeests (ConnochaeUs taurinus), and zebras(Equus burchelli) than expected. Second, preferred prey typesof lions were identified using conditional logit analysis. Lionspreferred to hunt small prey groups, groups that were closerthan 200 m, and groups that contained wart hogs, wildebeests,or zebras. Third, a risk-minimization optimal foraging modeland a rate-maximization model were used to predict lion preferences.The foraging theory models predict that preferences should changewith season and with lion group size. Qualitative support wasfound for most of these predictions.     

Collicular responses to the frequency modulated final part of echolocation sounds in Rhinolophus ferrum equinum

Summary Collicular evoked potentials in Rhinolophus ferrum equinum show very prominent responses to the final frequency modulated part of a acoustic stimulus, simulating the natural echolocation sound.     

A model of the visual localization of prey by frog and toad

In this paper we demonstrate how prey localization can be acheived rapidly and accurately by coupling prey-selection and lens-accommodation processes within a feedback loop. Information derived from prey selection supplies a setpoint for accomodation. In turn, adjustment of the lens modifies the visual input and can alter the prey selection process. The natural feedback of this goal-seeking system automatically corrects for the problem of ambiguity in binocular matching.Although it is of general interest as a depth algorithm, we tie the model to the known anatomy, physiology and behavior of frogs and toads. Instead of building a global depth-map we propose that the goal of catching a prey leads a frog or toad to select a particular region of its visual world for special scrutiny. We suggest that the first step of the prey-catching sequence is to adjust the accommodative state of the lenses and thus lock the visual apparatus on to a stimulus. We identify brain regions that could provide the neural substrates necessary to support the model's various functional stages and present experiments, with a computer simulation, that compare its functioning to animal behavior.     

Use of vision in prey detection by brown long-eared bats, Plecotus auritus

We investigated the ability of brown long-eared bats to make use of visual cues when searching for food. By using petri dishes containing mealworms that were subjected to different levels of illumination, we presented four bats with different sensory cues: visual, sonar and a combination of these. The bats preferred situations where both sonar cues and visual cues were available, and the visual information was more important than the sonar cues. The bats did, however, emit echolocation calls throughout the experiments. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

The energy cost of echolocation in pipistrelle bats (Pipistrettus pipistrellus)

Summary A positive relationship was established between energy expenditure and pulse rate of echolocation for 8 pipistrelle bats (Pipistrellus pipistrellus) when hanging at rest in a respirometry chamber at 28 °C. The least squares fit equation: Energy expenditure (J·^–1·h^–1)=110.09+ 40.3 pulse rate (n/s) explained 14% of the minute by minute variation in energy expenditure. For a 6 g bat therefore each pulse costs approximately 0.067 Joules to produce. The net cost of echolocation at 10 pulses per second for a 6 g pipistrelle bat was predicted to be 9.5 × BMR with a range of 7.0–12.2 × BMR. We suggest that since a major portion of the cost of echolocation may result from contraction of the pectoralis and scapularis groups of muscles, the cost of echolocation is reduced for flying animals which contract these muscles anyway during flight. This may account for the high incidence of echolocation systems amongst flying vertebrates, when compared with terrestrial species.     

Predation by xanthid crabs on early post-settlement gastropods: the role of prey size, prey density, and habitat complexity

Small predators in marine benthic communities create a hazardous environment for newly settled invertebrates, especially for the smallest individuals. To explore the effects of predation on a newly settled gastropod, queen conch (Strombus gigas Linnaeus), by a xanthid crab (Micropanope sp.), prey size, prey density, and habitat complexity were manipulated in five laboratory experiments. All crabs >3.1 mm CW killed all conch <2 mm SL when individual crabs (<14 mm carapace width (CW)) were offered individual conch that were 2–35 days old after metamorphosis (1.2–8.8 mm shell length (SL)). Only 10% of the crabs >5.0 mm CW, however, killed conch that were >5.0 mm SL, suggesting that conch may reach a size refuge from xanthid crabs at 5 mm SL. Furthermore, when given a choice, crabs (4.8 mm CW) preferred smaller conch (2.0 mm SL) to larger (3.7 mm SL), suggesting that 1 week of additional growth in shell length is advantageous to survivorship. Proportional mortality decreased as conch density increased when crabs were offered conch at seven different densities (two to 96 individuals). Crabs proved to be effective predators regardless of the amount of seagrass structure provided in a microcosm experiment, and could consume two conch in 10 s. The high densities of xanthid crabs that occur in the wild, their effectiveness as predators, and their large appetites point to the important role that small predators may potentially play in structuring the population dynamics of their small prey immediately after settlement.     

The role of olfaction and vision in the foraging behaviour of an echolocating megachiropteran fruit bat,Rousettus leschenaulti (Pteropodidae)

Many mammals use multimodal sensory information to find their food in complex environments. We studied the roles of olfactory and visual cues in the foraging behaviour of Rousettus leschenaulti, a tongue-clicking megachiropteran bat. We conducted experiments by offering a whole fruit, mashed fruit without shape and an artificial fruit to R. leschenaulti in dim light as well as in total darkness. R. leschenaulti responded to whole guava fruit and mashed guava fruit even in total darkness, whereas, artificial fruit similar to real fruit in size, shape and structure was ignored even when illuminated. These results reveal that odour may act as the primary cue for R. leschenaulti in finding fruit.     

The role of the medial geniculate bodies in analyzing sounds]

Elaboration and manifestation of motor alimentary conditioned reflexes were studied after a lesion of medial geniculate bodies (MGB) in adult cats. No substantial disturbance were recorded of the capacity for pitch analysis. In the case of more extensive MGB lesions, there were some difficulties in the elaboration of tone differentiations but not in their achievement. Additional temporo-parietal cortical ablation drastically reduced the animals' capacity for anlysing sound frequencies and more profoundly disturbed their capacity for inhibitory reactions.     

Sperm whale behaviour indicates the use of echolocation click buzzes "creaks" in prey capture

During foraging dives, sperm whales (Physeter macrocephalus) produce long series of regular clicks at 0.5-2 s intervals interspersed with rapid-click buzzes called "creaks". Sound, depth and orientation recording Dtags were attached to 23 whales in the Ligurian Sea and Gulf of Mexico to test whether the behaviour of diving sperm whales supports the hypothesis that creaks are produced during prey capture. Sperm whales spent most of their bottom time within one or two depth bands, apparently feeding in vertically stratified prey layers. Creak rates were highest during the bottom phase: 99.8% of creaks were produced in the deepest 50% of dives, 57% in the deepest 15% of dives. Whales swam actively during the bottom phase, producing a mean of 12.5 depth inflections per dive. A mean of 32% of creaks produced during the bottom phase occurred within 10 s of an inflection (13x more than chance). Sperm whales actively altered their body orientation throughout the bottom phase with significantly increased rates of change during creaks, reflecting increased manoeuvring. Sperm whales increased their bottom foraging time when creak rates were higher. These results all strongly support the hypothesis that creaks are an echolocation signal adapted for foraging, analogous to terminal buzzes in taxonomically diverse echolocating species.