Aerial insectivorous bat activity in relation to moonlight intensity

It is commonly assumed that aerial insectivorous bats in the tropics respond to moonlight intensity by decreasing their foraging activity during bright nights due either to an increase in predation risk, or to a reduction in insect availability.The effect of moonlight on bat activity can be measured both between nights and within a single night. However, few studies have simultaneously used both approaches, and most authors generally compare bat activity with lunar phases. Our main aim was to evaluate how moonlight influences aerial insectivorous bat activity at different time scales: between nights and within the same night. Activity of five bat species was measured using autonomous ultrasound recording stations and moonlight intensity percentages retrieved from the Moontool program nightly throughout a 53-day sampling period. Only one species (Myotis riparius) responded negatively to moonlight, while two species (Pteronotus parnellii and Saccopteryx leptura) increased their foraging activity in moonlight. For Cormura brevirostris and S. bilineata, moonlight intensity did not affect activity level. Bat activity was greater for all species at the beginning of the night, independent of the presence of the moon, indicating that foraging just after the sunset is adaptive. Thus, bat response to the effect of moonlight intensity is more apparent between nights than within a single night and may depend on species-specific traits, such as flight speed, flexibility in habitat use and body size.     

Extracting spatial networks from capture–recapture data reveals individual site fidelity patterns within a marine mammal’s spatial range

1. Estimating the impacts of anthropogenic disturbances requires an understanding of the habitat‐use patterns of individuals within a population. This is especially the case when disturbances are localized within a population''s spatial range, as variation in habitat use within a population can drastically alter the distribution of impacts.
2. Here, we illustrate the potential for multilevel binomial models to generate spatial networks from capture–recapture data, a common data source used in wildlife studies to monitor population dynamics and habitat use. These spatial networks capture which regions of a population''s spatial distribution share similar/dissimilar individual usage patterns, and can be especially useful for detecting structured habitat use within the population''s spatial range.
3. Using simulations and 18 years of capture–recapture data from St. Lawrence Estuary (SLE) beluga, we show that this approach can successfully estimate the magnitude of similarities/dissimilarities in individual usage patterns across sectors, and identify sectors that share similar individual usage patterns that differ from other sectors, that is, structured habitat use. In the case of SLE beluga, this method identified multiple clusters of individuals, each preferentially using restricted areas within their summer range of the SLE.
4. Multilevel binomial models can be effective at estimating spatial structure in habitat use within wildlife populations sampled by capture–recapture of individuals, and can be especially useful when sampling effort is not evenly distributed. Our finding of a structured habitat use within the SLE beluga summer range has direct implications for estimating individual exposures to localized stressors, such as underwater noise from shipping or other activities.

     

Bats in a changing landscape: Linking occupancy and traits of a diverse montane bat community to fire regime

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Differences in seasonal survival suggest species‐specific reactions to climate change in two sympatric bat species

Long‐lived animals with a low annual reproductive output need a long time to recover from population crashes and are, thus, likely to face high extinction risk, if the current global environmental change will increase mortality rates. To aid conservation of those species, knowledge on the variability of mortality rates is essential. Unfortunately, however, individual‐based multiyear data sets that are required for that have only rarely been collected for free‐ranging long‐lived mammals. Here, we used a five‐year data set comprising activity data of 1,445 RFID‐tagged individuals of two long‐lived temperate zone bat species, Natterer's bats (Myotis nattereri) and Daubenton's bats (Myotis daubentonii), at their joint hibernaculum. Both species are listed as being of high conservation interest by the European Habitats Directive. Applying mixed‐effects logistic regression, we explored seasonal survival differences in these two species which differ in foraging strategy and phenology. In both species, survival over the first winter of an individual's life was much lower than survival over subsequent winters. Focussing on adults only, seasonal survival patterns were largely consistent with higher winter and lower summer survival but varied in its level across years in both species. Our analyses, furthermore, highlight the importance of species‐specific time periods for survival. Daubenton's bats showed a much stronger difference in survival between the two seasons than Natterer's bats. In one exceptional winter, the population of Natterer's bats crashed, while the survival of Daubenton's bats declined only moderately. While our results confirm the general seasonal survival pattern typical for hibernating mammals with higher winter than summer survival, they also show that this pattern can be reversed under particular conditions. Overall, our study points toward a high importance of specific time periods for population dynamics and suggests species‐, population‐, and age class‐specific responses to global climate change.     

Turning to the dark side: LED light at night alters the activity and species composition of a foraging bat assemblage in the northeastern United States

Artificial light at night (ALAN) is a rapidly intensifying form of environmental degradation that can impact wildlife by altering light‐mediated physiological processes that control a broad range of behaviors. Although nocturnal animals are most vulnerable, ALAN''s effects on North American bats have been surprisingly understudied. Most of what is known is based on decades‐old observations of bats around street lights with traditional lighting technologies that have been increasingly replaced by energy‐efficient broad‐spectrum lighting, rendering our understanding of the contemporary effects of ALAN on North American bats even less complete. We experimentally tested the effects of broad‐spectrum ALAN on presence/absence, foraging activity, and species composition in a Connecticut, USA bat community by illuminating foraging habitat with light‐emitting diode (LED) floodlights and comparing acoustic recordings between light and dark conditions. Lighting dramatically decreased presence and activity of little brown bats (Myotis lucifugus), which we detected on only 14% of light nights compared with 65% of dark (lights off) and 69% of control (lights removed) nights. Big brown bat (Eptesicus fuscus) activity on light nights averaged only half that of dark and control nights. Lighting did not affect presence/absence of silver‐haired bats (Lasionycteris noctivagans), but decreased their activity. There were no effects on eastern red bats (Lasiurus borealis) or hoary bats (L. cinereus), which have been described previously as light‐tolerant. Aversion to lighting by some species but not others caused a significant shift in community composition, thereby potentially altering competitive balances from natural conditions. Our results demonstrate that only a small degree of ALAN can represent a significant form of habitat degradation for some North American bats, including the endangered little brown bat. Research on the extent to which different lighting technologies, colors, and intensities affect these species is urgently needed and should be a priority in conservation planning for North America''s bats.     

Roosting and Foraging Behavior of Two Neotropical Gleaning Bats,Tonatia silvicola and Trachops cirrhosus (Phyllostomidae)1

We studied roosting and foraging behavior of two Neotropical gleaning bats, ?Orbigny's round-eared bat, Tonatia silvicola, and the fringe-lipped bat, Trachops cirrhosus (Phyllostomidae). Techniques included radio-tracking in a tropical lowland forest in Panama and analysis of data from long-term studies in Panama and Venezuela. Day roosts of T. silvicola were in arboreal termite nests. T. cirrhosus roosted in a hollow tree. T. silvicola emerged late (ca 60 min after sunset), and foraged close to the roosts (maximum distance 200–500 m). T. cirrhosus emerged early (ca 30 min after local sunset), and foraged farther from its roost (>1.5 km). Both bats used small foraging areas (3–12 ha) in tall, open forest. They foraged in continuous flight (maximum 27–36 min) or in short sally flights (<1 minute) from perches (“hang-and-wait” strategy). The small foraging areas of these bats and their sedentary foraging mode most likely make them vulnerable to habitat fragmentation.     

Optimizing ultrasonic sampling effort for monitoring forest bats

Landscape‐scale monitoring is a key approach for assessing changes in indicators. However, great care needs to be taken to collect rigorous data and avoid wasting resources in long‐term programmes. Insect‐eating bats are diverse, functionally important and are often proposed as indicator species of environmental health. We used acoustic (ultrasonic) data from pilot bat surveys undertaken in forests and woodlands to optimize sampling effort to produce precise estimates of bat activity and occupancy. We also carried out simulations to evaluate the statistical power of different sampling designs to detect changes in activity and occupancy levels of individual bat species. There was little gain in precision for estimates of bat activity by sampling beyond five to six detector nights. To ensure spatial heterogeneity was sampled around a monitoring point, three detectors for two nights or two detectors for three nights would be required. This level of sampling was also sufficient to be 90% certain of recording occupancy for 11 of 12 taxa. Power simulations revealed that a sampling design using two detectors per monitoring point for two nights could detect a 30% decline within 10 years with 90% power for all species, except the white‐striped free tail bat (Tadarida australis), using either changes in activity levels or occupancy. However, fewer years were required when using occupancy. Setting detectors either on‐flyways or off‐flyways contributed only minor differences to the time taken to reach 90% power for both occupancy and activity levels, though sampling both locations has major implications for interpreting trends in bats. We suggest that bat activity levels are more sensitive for detecting change than occupancy because one pass or 1000 passes can be recorded per night by an acoustic detector, and this is not differentiated by occupancy. Bats can be monitored cost‐effectively and should be included in monitoring programmes.     

Sex-related differences in roost-site selection by Daubenton's bats Myotis daubentonii during the nursery period

• 1 We investigated sex-related differences in roost-site selection by Daubenton's bats Myotis daubentonii in their summer habitat in central Germany. We studied whether the location of and landscape structure around nine nursery roosts and seven male-only roosts differed during the nursery period (15 May−31 July). Roosts were located by radio-tracking, and animal numbers and group composition were obtained by trapping and counting at roosts. Landscape structure was evaluated by a GIS-based habitat analysis.
• 2 Marked variation in animal numbers was observed both in nursery roosts (range: 6–144 individuals) and male roosts (range: 1–51 individuals). The surroundings of nursery and male roosts varied significantly in the proportion of areas belonging to different landscape elements. The areas covered by ponds, lakes and rivers, as well as the area covered by coppices were larger in the surroundings of nursery roosts. Moreover, nursery roosts lay closer to a river and at lower altitudes than male roosts. Male Daubenton's bats used more distant foraging sites than gravid or lactating females.
• 3 The differences in roost-site location between the two sexes are suggestive of intraspecific competition for access to productive foraging areas in the surroundings of the summer roosts, with females being dominant over males. We assume that breeding females defend climatically favourable areas with good food supply in order to increase the survival of their offspring.

     

Estimating population density of insectivorous bats based on stationary acoustic detectors: A case study

1. Automated recording units are commonly used by consultants to assess environmental impacts and to monitor animal populations. Although estimating population density of bats using stationary acoustic detectors is key for evaluating environmental impacts, estimating densities from call activity data is only possible through recently developed numerical methods, as the recognition of calling individuals is impossible.
2. We tested the applicability of generalized random encounter models (gREMs) for determining population densities of three bat species (Common pipistrelle Pipistrellus pipistrellus, Northern bat Eptesicus nilssonii, and Natterer's bat Myotis nattereri) based on passively collected acoustical data. To validate the results, we compared them to (a) density estimates from the literature and to (b) Royle–Nichols (RN) models of detection/nondetection data.
3. Our estimates for M. nattereri matched both the published data and RN‐model results. For E. nilssonii, the gREM yielded similar estimates to the RN‐models, but the published estimates were more than twice as high. This discrepancy might be because the high‐altitude flight of E. nilssonii is not accounted for in gREMs. Results of gREMs for P. pipistrellus were supported by published data but were ~10 times higher than those of RN‐models. RN‐models use detection/nondetection data, and this loss of information probably affected population estimates of very active species like P. pipistrellus.
4. gREM models provided realistic estimates of bat population densities based on automatically recorded call activity data. However, the average flight altitude of species should be accounted for in future analyses. We suggest including flight altitude in the calculation of the detection range to assess the detection sphere more accurately and to obtain more precise density estimates.

     

Resource selection by Indiana bats during the maternity season

Little information exists on resource selection by foraging Indiana bats (Myotis sodalis) during the maternity season. Existing studies are based on modest sample sizes because of the rarity of this endangered species and the difficulty of radio-tracking bats. Our objectives were to determine resource selection by foraging Indiana bats during the maternity season and to compare resource use between pregnant and lactating individuals. We used an information theoretic approach with discrete choice modeling based on telemetry data to evaluate our hypotheses that land cover, percent canopy cover, distance to water, and prescribed fire affected the relative probability a point was used by a foraging Indiana bat. We fit models for individual bats and a population-level model based on all individuals with a random factor to account for differences in sample size among individuals. We radio-tracked 29 individuals and found variation in resource selection among individuals. However, among individuals with the same supported covariates, the magnitude and direction of the covariates were similar. Eighteen bats selected areas with greater canopy closure and 5 of 6 bats that had areas burned by low-intensity prescribed fire in their home range selected burned areas. Resource selection was related to land cover for 13 individuals; they selected forest and shrubland over agricultural land, which composed >50% of the landscape within 10 km. We found no support for our hypothesis that resource selection was related to individual reproductive condition or Julian date in our population-level model indicating habitat selection was not determined by reproductive status or date within the maternity season. Land use or forest management that greatly reduces canopy cover may have a negative impact on Indiana bat use. Maintaining forest cover in agricultural landscapes is likely critical to persistence of maternity colonies in these landscapes. Sites managed with low severity prescribed fire may be selected by some individuals because of reduced understory vegetation. © 2013 The Wildlife Society.     

Behavioural context of multi-scale species distribution models assessed by radio-tracking

Incorporating ecological processes and animal behaviour into Species Distribution Models (SDMs) is difficult. In species with a central resting or breeding place, there can be conflict between the environmental requirements of the ‘central place’ and foraging habitat. We apply a multi-scale SDM to examine habitat trade-offs between the central place, roost sites, and foraging habitat in Myotis nattereri. We validate these derived associations using habitat selection from behavioural observations of radio-tracked bats. A Generalised Linear Model (GLM) of roost occurrence using land cover variables with mixed spatial scales indicated roost occurrence was positively associated with woodland on a fine scale and pasture on a broad scale. Habitat selection of radio-tracked bats mirrored the SDM with bats selecting for woodland in the immediate vicinity of individual roosts but avoiding this habitat in foraging areas, whilst pasture was significantly positively selected for in foraging areas. Using habitat selection derived from radio-tracking enables a multi-scale SDM to be interpreted in a behavioural context. We suggest that the multi-scale SDM of M. nattereri describes a trade-off between the central place and foraging habitat. Multi-scale methods provide a greater understanding of the ecological processes which determine where species occur and allow integration of behavioural processes into SDMs. The findings have implications when assessing the resource use of a species at a single point in time. Doing so could lead to misinterpretation of habitat requirements as these can change within a short time period depending on specific behaviour, particularly if detectability changes depending on behaviour.     

The spatial ecology of the whiskered bat (Myotis mystacinus) at the western extreme of its range provides evidence of regional adaptation

Although widespread, the ecology of the whiskered bat, Myotis mystacinus in Europe remains poorly understood. Ireland is positioned at the most western extreme of this species’ range. To ascertain the ecology of M. mystacinus at its geographic range extreme, the roosting behaviour, home range and habitat use of females in a maternity roost in Ireland was investigated by radio-tracking. M. mystacinus were active in a diversity of habitats: namely, mixed woodland, riparian vegetation, arable land and rough grassland. However, only mixed woodland and riparian habitats were selected as core foraging areas. This is in contrast to a previous study from Britain where only pasture was utilised but is in agreement with data from Slovakia, where woodland was also selected, whilst riparian areas were also utilised by this species in Germany. A high degree of overlap in the foraging areas of individuals was observed. A total of seven roosts were utilised by tracked bats and roost switching behaviour was observed. We discuss our contrasting results in respect to range limitations, regional variability in landscape structure and the composition of bat communities. The present results have implications for the conservation of M. mystacinus within Ireland and other parts of its range, highlighting the need for range wide ecological studies. Regional variability in the ecology of bats related to landscape factors is an important consideration for bat conservation and therefore must be incorporated into future management plans.     

State‐space modeling reveals habitat perception of a small terrestrial mammal in a fragmented landscape

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Activity patterns of long‐tailed bats (Chalinolobus tuberculatus) in a rural landscape,South Canterbury,New Zealand

Abstract

The temporal and spatial activity patterns of long‐tailed bats (Chalinolobus tuberculatus) were assessed between January and July 1995 by automatic monitoring of echolocation calls, radio‐telemetry and direct observation at Hanging Rock, South Canterbury. Automatic bat detection units recorded 8728 bat passes and 933 feeding buzzes during 272 nights of sampling. In addition, five radio‐tagged post‐lactating female bats were each followed for an average of 13.0 ± 3.2 (SE) days. Home range size averaged 471.4 ± 50.9 ha (95% median minimum convex polygons) but core areas of activity (50% of fixes) were 54.4 ± 5.4 ha (11.6 ± 3.1% of the home range size). Patterns of activity varied in relation to time of year, time of night, temperature, invertebrate activity and habitat. Between January and March, long‐tailed bats consistently emerged from day roosts at sunset and flew throughout the night, with peaks of activity shortly after sunset and before sunrise. After the beginning of April, long‐tailed bats no longer flew throughout the night, but they had one peak of activity between the first and third hour after sunset. Both automatic monitoring and radio‐telemetry showed extensive use by long‐tailed bats of river and riparian habitats. Radio‐tagged bats avoided foraging over open farmland, and repeatedly returned to the same sites on consecutive nights.     

Behavioural plasticity and trophic niche shift: How wintering geese respond to habitat alteration

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Activity Pattern of the Trawling Phyllostomid Bat,Macrophyllum macrophyllum,in Panamá1

We studied activity patterns of long‐legged bats, Macrophyllum macrophyllum (Phyllostomidae), in the Barro Colorado Nature Monument, Panamá, using radio‐telemetry. Activity of four males and five females equipped with radio‐transmitters were monitored for 4–7 entire nights each between April and July 2002. Bats exhibited maximum activity around dusk and high activity during the night. Males and females foraged for equal amounts of time in continuous flight (mean: 7 min, maximum 1 h) with interspersed resting phases (mean: 15 min, maximum 3 h). Activity of M. macrophyllum was sensitive to several factors. Time of emergence and return to day roost were correlated with time of sunset and sunrise, respectively. Maximum bat activity coincided with high abundance of aerial insects. Finally, heavy rain caused bats to reduce or cease flight activity. Direct observations and field video recordings support the assumption that M. macrophyllum employs two distinct foraging modes: trawling of insects from and capture of aerial insects at low heights above water. Combination of foraging modes gives M. macrophyllum high flexibility and efficiency in prey search. Activity, foraging mode, and morphology, which are similar to trawling bats from other families, distinguish M. macrophyllum from all other phyllostomid species and grant it access to open habitat above water, a habitat no other phyllostomid bat has conquered.     

Seasonal variation in the diet of the serotine bat (Eptesicus serotinus): A high-resolution analysis using DNA metabarcoding

Bats play an important role as predators of insect populations but are threatened by a variety of factors, including the loss of foraging habitat and insect declines. Knowledge on trophic interactions, foraging strategies, and hunting areas is key to understanding the ecology of bat species, to assess their impact on ecosystems and to optimize conservation strategies. We investigated seasonal trends in the diet of two nursery colonies of the serotine bat, Eptesicus serotinus, from an intensively farmed agricultural landscape in Germany. Using DNA-metabarcoding of food remains in bat droppings collected from May to July 2018, we identified 254 taxa of 13 arthropod orders to species or genus level, including numerous pest species. Our results indicate an equal use of Coleoptera, Diptera, and Lepidoptera, contradicting previous morphological dietary analyses that had shown beetles to be the most frequent prey. The dietary composition was seasonally highly variable and mainly determined by prey phenology. Dietary richness significantly increased throughout the sampling period, reflecting increasing insect activity with progressing season. Our findings demonstrate that E. serotinus is a generalist forager, linking different habitat types through trophic interactions.     

How citizen science could improve species distribution models and their independent assessment

1. Species distribution models (SDM) have been increasingly developed in recent years, but their validity is questioned. Their assessment can be improved by the use of independent data, but this can be difficult to obtain and prohibitive to collect. Standardized data from citizen science may be used to establish external evaluation datasets and to improve SDM validation and applicability.
2. We used opportunistic presence‐only data along with presence–absence data from a standardized citizen science program to establish and assess habitat suitability maps for 9 species of amphibian in western France. We assessed Generalized Additive and Random Forest Models’ performance by (1) cross‐validation using 30% of the opportunistic dataset used to calibrate the model or (2) external validation using different independent datasets derived from citizen science monitoring. We tested the effects of applying different combinations of filters to the citizen data and of complementing it with additional standardized fieldwork.
3. Cross‐validation with an internal evaluation dataset resulted in higher AUC (Area Under the receiver operating Curve) than external evaluation causing overestimation of model accuracy and did not select the same models; models integrating sampling effort performed better with external validation. AUC, specificity, and sensitivity of models calculated with different filtered external datasets differed for some species. However, for most species, complementary fieldwork was not necessary to obtain coherent results, as long as the citizen science data were strongly filtered.
4. Since external validation methods using independent data are considered more robust, filtering data from citizen sciences may make a valuable contribution to the assessment of SDM. Limited complementary fieldwork with volunteer''s participation to complete ecological gradients may also possibly enhance citizen involvement and lead to better use of SDM in decision processes for nature conservation.

     

Interspecific competition in bats: state of knowledge and research challenges

1. Interspecific competition (IC) is often seen as a main driver of evolutionary patterns and community structure. Bats might compete for key resources, and cases of exaggerated divergence of resource-related characters or trait overdispersion in bat assemblages are often explained in terms of current or past interspecific competition. However, other pressures leading to patterns that mimic the outcome of competition cannot always be ruled out.
2. We present the state of knowledge on IC among bats, providing a critical evaluation of the information available and identifying open questions and challenges.
3. We reviewed 100 documents addressing potential or actual IC in bats and categorised them in terms of the resource for which bats compete (food, foraging habitat, roosts, water, and acoustic space). We also examined the ecomorphological and behavioural traits considered therein to highlight responses to IC or niche partitioning.
4. We found that: although resources should be limiting in order for competition to occur, this is seldom tested; sympatry is sometimes taken as synonymous of syntopy (yet sympatric species that are not syntopic will never experience competition); comparisons between sympatry and allopatry are rare; and testing of objective criteria exploring the existence of niche partitioning or character displacement is not commonly adopted.
5. While morphological examination of food remains in droppings has often led to coarse-grained analysis that proved insufficient to establish the occurrence of food niche overlap or partitioning, new frontiers are being opened by state-of-the-art molecular dietary analysis.
6. A better understanding of IC in bats is paramount, since distributional changes leading to novel bat assemblages driven by climate change are already taking place, and the dramatic decline in insect availability, as well as the global loss or alteration of foraging habitat, may generate new competitive interactions or exacerbate existing interactions in the Anthropocene, and into the future.

     

Roosting and Foraging Social Structure of the Endangered Indiana Bat (Myotis sodalis)

Social dynamics are an important but poorly understood aspect of bat ecology. Herein we use a combination of graph theoretic and spatial approaches to describe the roost and social network characteristics and foraging associations of an Indiana bat (Myotis sodalis) maternity colony in an agricultural landscape in Ohio, USA. We tracked 46 bats to 50 roosts (423 total relocations) and collected 2,306 foraging locations for 40 bats during the summers of 2009 and 2010. We found the colony roosting network was highly centralized in both years and that roost and social networks differed significantly from random networks. Roost and social network structure also differed substantially between years. Social network structure appeared to be unrelated to segregation of roosts between age classes. For bats whose individual foraging ranges were calculated, many shared foraging space with at least one other bat. Compared across all possible bat dyads, 47% and 43% of the dyads showed more than expected overlap of foraging areas in 2009 and 2010 respectively. Colony roosting area differed between years, but the roosting area centroid shifted only 332 m. In contrast, whole colony foraging area use was similar between years. Random roost removal simulations suggest that Indiana bat colonies may be robust to loss of a limited number of roosts but may respond differently from year to year. Our study emphasizes the utility of graphic theoretic and spatial approaches for examining the sociality and roosting behavior of bats. Detailed knowledge of the relationships between social and spatial aspects of bat ecology could greatly increase conservation effectiveness by allowing more structured approaches to roost and habitat retention for tree-roosting, socially-aggregating bat species.