Acoustic perception of landscape elements by the pond bat (Myotis dasycneme)

What determines the information update rate in echolocating bats

The rate of sensory update is one of the most important parameters of any sensory system. The acquisition rate of most sensory systems is fixed and has been optimized by evolution to the needs of the animal. Echolocating bats have the ability to adjust their sensory update rate which is determined by the intervals between emissions - the inter-pulse intervals (IPI). The IPI is routinely adjusted, but the exact factors driving its regulation are unknown. We use on-board audio recordings to determine how four species of echolocating bats with different foraging strategies regulate their sensory update rate during commute flights. We reveal strong correlations between the IPI and various echolocation and movement parameters. Specifically, the update rate increases when the signals' peak-energy frequency and intensity increases while the update rate decreases when flight speed and altitude increases. We suggest that bats control their information update rate according to the behavioral mode they are engaged in, while always maintaining sensory continuity. Specifically, we suggest that bats apply two modes of attention during commute flights. Our data moreover suggests that bats emit echolocation signals at accurate intervals without the need for external feedback.

Qualitative synthesis of temperate bat responses to silvicultural treatments—where do we go from here?

Most bat species depend on forests for roosting, foraging, and drinking during part or all of their life cycles. Many of the world’s forests are managed using a variety of silvicultural treatments and, over the past 40 years, researchers have studied the responses of bats to these treatments. I carried out a qualitative synthesis of the literature on roosting and foraging responses of temperate insectivorous bats to silvicultural treatments at the stand level to determine what treatments may be most compatible with conservation and to guide future research. Eighty-eight studies from Canada, the United States, Europe, Australia, and New Zealand, met review criteria. Based on my results, foraging and commuting habitat use was less affected by changes in forest structure and composition than roost habitat use. Mid-rotation treatments that reduce clutter while retaining overstory structure (e.g., thinning and fire) had more neutral and positive effects than treatments that removed all or most of the overstory. Based on an examination of the methods and assumptions of the 88 studies included in this review, I conclude that future studies should: 1) strive to account for treatment effects on detection probability of bats when using acoustic detectors; 2) examine responses of bats to silvicultural treatments outside the maternity season; 3) examine demographic and physiological responses to silvicultural treatments in addition to habitat use to fully understand the effects of these treatments on bat populations; and 4) use stand-level data to model forest management effects across large landscapes and over long time periods.

Place recognition using batlike sonar

Echolocating bats have excellent spatial memory and are able to navigate to salient locations using bio-sonar. Navigating and route-following require animals to recognize places. Currently, it is mostly unknown how bats recognize places using echolocation. In this paper, we propose template based place recognition might underlie sonar-based navigation in bats. Under this hypothesis, bats recognize places by remembering their echo signature - rather than their 3D layout. Using a large body of ensonification data collected in three different habitats, we test the viability of this hypothesis assessing two critical properties of the proposed echo signatures: (1) they can be uniquely classified and (2) they vary continuously across space. Based on the results presented, we conclude that the proposed echo signatures satisfy both criteria. We discuss how these two properties of the echo signatures can support navigation and building a cognitive map.

Group size and dispersal ploys: an analysis of commuting behaviour of the pond bat (Myotis dasycneme)

Like most bat species, the pond bat (Myotis dasycneme (Boie, 1825)) lives in roosts more or less in the centre of their foraging habitat and are considered central-place foragers. Commuting routes, or flyways, between roosts and hunting areas have an essential ecological function for bats. We summarize the results of research performed on the commuting routes of pond bats between 2002 and 2009. We give, among others, a description on how bats disperse, how to recognize a commuting route, and details about the effort needed to make a complete survey of one commuting route. Furthermore, we make a relation between number of animals on the route and size of their respective roost. The results suggest pond bats are not completely reliant on waterways for reaching their foraging habitat; they use directional dispersal, following commuting routes over waterways in combination with shortcuts over land. These results provide information that can be used to better understand how bats use their commuting routes. Also, the knowledge can be applied to survey work.

Do predators influence the behaviour of bats?

Many aspects of animal behaviour are affected by real-time changes in the risk of predation. This conclusion holds for virtually all taxa and ecological systems studied, but does it hold for bats? Bats are poorly represented in the literature on anti-predator behaviour, which may reflect a lack of nocturnal predators specialized on bats. If bats actually experience a world with minimal anti-predator concerns, then they will provide a unique contrast within the realm of vertebrate ecology. Alternatively, such predator-driven behaviour in bats may not yet be fully understood, given the difficulties in working with these highly mobile and nocturnal animals. We provide a wide-ranging exploration of these issues in bat behaviour. We first cover the basic predator-prey information available on bats, both on potential predators and the ways in which bats might perceive predators and respond to attacks. We then cover work relevant to key aspects of bat behaviour, such as choice of daytime roosts, the nature of sleep and torpor, evening roost departures, moonlight avoidance, landscape-related movement patterns, and habitat selection. Overall, the evidence in favour of a strong influence of predators on bat behaviour is equivocal, with the picture clouded by contradictory results and a lack of information on potential predators and the perception of risk by bats. It seems clear that day-active bats run a considerable risk of being killed by diurnal raptors, which are able to capture bats with relative ease. Thus, bats taking advantage of a pulse of insects just prior to sunset are likely taking risks to gain much-needed energy. Further, the choice of daytime roosts by bats is probably strongly influenced by roost safety. Few studies, however, have directly addressed either of these topics. As a group, insectivorous temperate-zone bats show no clear tendency to avoid apparently risky situations, such as activity on moonlit nights. However, some observations are consistent with the idea that predation risk affects choice of movement paths and feeding areas by temperate-zone bats, as well as the timing of roost departures. The behaviour of tropical bats, on the other hand, seems more generally influenced by predators; this is especially true for tropical nectarivores and frugivores, but also for insectivorous bats. Presumably there are more serious predators on bats in the tropics (e.g. specialized raptors or carnivorous bats), but the identity of these predators is unclear. More information is needed to assess fully the influence of predators on bat behaviour. There is much need for work on the ways in which bats perceive predators via auditory, visual, and olfactory cues, and whether bats have some knowledge of the risks posed by different predators. Also needed is information on how predators attack bats and how bats react to attacking predators. Difficult to obtain, but of critical value, will be information on the nature of the predation risk experienced by bats while away from roosts and during the full darkness of night.

Street lighting disturbs commuting bats

Anthropogenic disturbance is a major cause of worldwide declines in biodiversity. Understanding the implications of this disturbance for species and populations is crucial for conservation biologists wishing to mitigate negative effects. Anthropogenic light pollution is an increasing global problem, affecting ecological interactions across a range of taxa and impacting negatively upon critical animal behaviors including foraging, reproduction, and communication (for review see). Almost all bats are nocturnal, making them ideal subjects for testing the effects of light pollution. Previous studies have shown that bat species adapted to foraging in open environments feed on insects attracted to mercury vapor lamps. Here, we use an experimental approach to provide the first evidence of a negative effect of artificial light pollution on the commuting behavior of a threatened bat species. We installed high-pressure sodium lights that mimic the intensity and light spectra of streetlights along commuting routes of lesser horseshoe bats (Rhinolophus hipposideros). Bat activity was reduced dramatically and the onset of commuting behavior was delayed in the presence of lighting, with no evidence of habituation. These results demonstrate that light pollution may have significant negative impacts upon the selection of flight routes by bats.

Flight and echolocation behaviour of three vespertilionid bat species while commuting on flyways

This study compares the flight and echolocation behaviour of three vespertilionid bat species while they commute on flyways. We measured the bats' spatial position relative to vertical background contours and relative to the ground while recording their echolocation behaviour. In Myotis daubentonii, we found a significant influence of spatial context on the position and dimensions of flyways as well as on echolocation behaviour. In gap situations, flyways tended to be narrower and located closer to background structures, flight speeds were lower and the bandwidth of echolocation signals was larger than in edge situations. Differences in background structure did not affect flight and echolocation behaviour. When commuting in the same gap situation flyway positions and dimensions for M. daubentonii and Myotis brandtii were similar but differed from those of Pipistrellus pipistrellus, which were slightly higher and further out than those used by the Myotis species. In M. brandtii, flyway positions and dimensions remained constant over 3 years. We found species-dependent differences in signal structure, but pulse interval and flight speed were similar across all species. The influence of available space on the position of flyways, on flight speed and on echolocation behaviour is discussed.

Spatial orientation in echolocating harbour porpoises (Phocoena phocoena)

Studies concerning the echolocation behaviour of odontocetes focus mainly on target detection and discrimination, either in stationary animals or in animals approaching a specific target. We present the first data on the use of echolocation for spatial orientation or navigation. Synchronised video and high-frequency recordings were made of two harbour porpoises trained to swim from one position to another across an outdoor pool in order to correlate swimming and echolocation behaviour. Both porpoises showed a clear range-locking behaviour on specific positions near the end of the pool, as indicated by a decrease in click interval with decreasing distance. The decrease in click interval followed the two-way-transit time, which is the time interval between the outgoing click and the received echo from the focal object. This suggests that the porpoises used focal objects as landmarks. The lag time, defined as the time between the arrival of an echo from a landmark and the emission of the next click, was task specific. The lag time was longer for difficult tasks (26–36 ms) and shorter for simpler tasks(14–19 ms), with some individual differences between the two animals. Our results suggest that echolocation by odontocetes is used not only for target detection, localisation and classification but also for spatial orientation.

Effects of food abundance and wind on the use of tree lines by an insectivorous bat, Pipistrellus pipistrellus

We tested the hypotheses that the distance bats fly from tree lines depend on food abundance and protection from wind. We monitored the activity of pipistrelle bats (Pipistrellus pipistrellus) and measured insect abundance and wind speed and direction at fixed distances up to 50 m from tree lines. We compared bat behaviour in different situations: with and without wind and with low and high insect abundances in adjacent open areas. In all situations, pipistrelle bats' activity decreased with increasing distance from the tree line. Within nights, we found no effect of wind speed on bat activity (sound recorded per 5 min) on the leeward side of the tree lines. Between nights, however, bats concentrated their activities closer to the tree lines at high wind speeds or angles of incidence of wind from 45° to 90°. A significant relationship between bat and insect abundances was found only when the tree line was bordered by insect-rich grassland. Since wind and insect abundance only partly explained the distances bats flew from tree lines, two alternative explanations, namely predator avoidance and the use of tree lines as acoustic landmarks, are discussed. Pipistrelle bats using a double row of trees as a commuting route at dusk flew mainly between the tree lines, regardless of insect abundance or wind speed. It is argued that predator avoidance explains this behaviour, being a constraint on movements of bats at relatively high light levels. At high wind speeds and angles of incidence greater than 45°, the proportion of pipistrelle bats commuting on the leeward side of the tree lines increased.