Physiological Ecology of Bat Migration

Migration is perhaps the most poorly understood aspect of bat biology and the underlying physiological basis is virtually unstudied. Although distantly related, bats and birds are both endothermic flying vertebrates and bird migration physiology has been studied for decades. Therefore, I used migratory birds as a model system to make predictions regarding the physiological ecology of bat migration. First, I compared brain size of migratory and sedentary bat species. Migratory species have smaller brains which suggests the costs of carrying and maintaining a large brain are incompatible with the demands of migration. Next, I studied silver-haired bats (Lasionycteris noctivagans) during migratory stopover. Bats arrived at the site with fat stores comparable to migratory birds, rarely foraged, and had short stopover durations. I proposed that bats use daily torpor to minimize energy expenditure during non-flight periods, thus sparing fuel stores for migratory flight. Finally, I compared body composition and flight muscle physiology in migrating and non-migrating hoary bats (Lasiurus cinereus). Changes in digestive and exercise organ sizes, the composition of adipose stores, and increased catabolic enzyme activities all reflected the increased energetic demands of migration. Sex-specific changes in muscle membrane fatty acid composition and the expression of fatty acid transport proteins suggest pregnant females are subject to different pressures than males. The energetic demands of bat migration lead to many physiological changes as observed in migratory birds. However, several factors specific to bats (especially heterothermy and the timing of reproduction) result in bat migration as a distinct phenomenon compared to birds

Seasonal Dynamics of Lipid Metabolism and Energy Storage in the Brazilian Free-Tailed Bat

As small, flying, mammalian endotherms, insectivorous bats are adapted to operate at high levels of energy expenditure. In response to seasonally variable challenges, we predicted that bats should balance energy budgets by flexibly adjusting aspects of their physiology or behavior in ways that elevate metabolic capacity. We examined variation in energy storage and pathways for oxidative metabolism in Brazilian free-tailed bats (Tadarida brasiliensis) related to estimated costs associated with reproduction and migration. We collected pectoral muscle and liver from female T. brasiliensis at six time points during the summer and fall and measured changes in the activity of four enzymes involved with lipid metabolism. Body mass varied substantially with life-cycle stage, suggesting that rapid accumulation and use of fat stores occurs in response to current and anticipated energy demands. Catabolic enzyme activity (carnitine palmitoyltransferase [CPT], 3-hydroxyacyl-CoA dehydrogenase [HOAD], and citrate synthase [CS]) in the muscle was increased during lactation compared with early pregnancy but exhibited no change before fall migration. While there was no temporal change in lipid biosynthetic capacity in the liver, fatty acid synthase activity was negatively correlated with body mass. Variation in body mass and enzyme activity in T. brasiliensis during the summer suggests that stored energy is mobilized and lipid oxidative capacity is increased during periods of increased demand and that lipid biosynthetic capacity is increased with depletion of fat stores. These results suggest that bats are able to flexibly adjust metabolic capacity based on energy requirement to maintain energy balance despite high levels of expenditure

Considerations of Varied Thermoregulatory Expressions in Migration Theory

This is the peer reviewed version of the following article: Considerations of Varied Thermoregulatory Expressions in Migration Theory, which has been published in final form at https://doi.org/10.1111/oik.08178. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.Optimal migration theory has been used for 3 decades to generate predictions of stopover behavior and understand migration ecology. Yet, to date, there have been no attempts to understand the impacts of thermoregulation on migration theory predictions of stopover behavior. Though most migrants are homeothermic, a diverse group of migrants from bats to hummingbirds and warblers make use of some degree of heterothermy. We consider how thermoregulation influences stopover fuel deposition rates, and thus alters optimal migration theory predictions of stopover behavior using a hypothetical migratory bat as a model organism. We update the analytical models of optimal migration theory by considering scenarios of fixed metabolic rate (the current assumption of optimal migration theory) and 3 different mass-specific metabolic rates including homeothermy, shallow torpor heterothermy, and deep torpor heterothermy. Our results predict that heterotherms will make shorter stopovers, have a decreased departure fuel load, and reduce the overall time and energy costs associated with stopovers relative to homeotherms, highlighting that thermoregulation can drastically influence stopover behavior and ultimately play a critical role in population level patterns of migration.Texas Tech University Department of Biological Sciences

Island biogeography theory and the urban landscape: stopover site selection by the silver-haired bat (Lasionycteris noctivagans)

Many migratory bats require forested sites for roosting and foraging along their migration path, but increased urbanization and intensive agricultural practices may reduce the availability of stopover sites. Urban forests may provide important stopover habitat, maintaining landscape connectivity in regions where the majority of natural habitat has been cleared for development. Island biogeography theory can be applied to urbanized temperate forest biomes where small urban forests represent islands separated from the larger “mainland” forest. We used acoustic monitoring during the fall migration period to investigate the use of urban forest habitat by the migratory species Lasionycteris noctivagans Le Conte, 1831. We predicted that recorded activity would have a positive relationship with forest patch area and shape and a negative relationship with isolation from other forest patches, as suggested by island biogeography theory. We observed greater activity at larger forest patches, and although relationships for shape and isolation were not statistically supported the observed patterns were consistent with predictions. Our results demonstrate the need for more in-depth research on the habitat requirements for both migratory and resident bat species and the impact that ongoing urbanization has on local bat populations.Natural Sciences and Engineering Research Council of Canada, RGPIN-2021-02639

Personality Variation in Little Brown Bats

Animal personality or temperament refers to individual differences in behaviour that are repeatable over time and across contexts. Personality has been linked to life-history traits, energetic traits and fitness, with implications for the evolution of behaviour. Personality has been quantified for a range of taxa (e.g., fish, songbirds, small mammals) but, so far, there has been little work on personality in bats, despite their diversity and potential as a model taxon for comparative studies. We used a novel environment test to quantify personality in little brown bats (Myotis lucifugus) and assess the short-term repeatability of a range of behaviours. We tested the hypothesis that development influences values of personality traits and predicted that trait values associated with activity would increase between newly volant, pre-weaning young-of-the-year (YOY) and more mature, self-sufficient YOY. We identified personality dimensions that were consistent with past studies of other taxa and found that these traits were repeatable over a 24-hour period. Consistent with our prediction, older YOY captured at a fall swarming site prior to hibernation had higher activity scores than younger YOY bats captured at a maternity colony, suggesting that personality traits vary as development progresses in YOY bats. Thus, we found evidence of short-term consistency of personality within individuals but with the potential for temporal flexibility of traits, depending on age."Funding was provided by a Natural Sciences and Engineering Research Council (NSERC) Canada Graduate Scholarship to AKM and post-doctoral fellowship to LPM as well as grants to CKRW from NSERC, the Canada Foundation for Innovation, the Manitoba Research and Innovation Fund and Manitoba Hydro Forest Enhancement Program."https://journals.plos.org/plosone/article?id=10.1371/journal.pone.008023

Learning When to Speak: Latency and Quality Trade-offs for Simultaneous Speech-to-Speech Translation with Offline Models

Recent work in speech-to-speech translation (S2ST) has focused primarily on offline settings, where the full input utterance is available before any output is given. This, however, is not reasonable in many real-world scenarios. In latency-sensitive applications, rather than waiting for the full utterance, translations should be spoken as soon as the information in the input is present. In this work, we introduce a system for simultaneous S2ST targeting real-world use cases. Our system supports translation from 57 languages to English with tunable parameters for dynamically adjusting the latency of the output -- including four policies for determining when to speak an output sequence. We show that these policies achieve offline-level accuracy with minimal increases in latency over a Greedy (wait-$k$) baseline. We open-source our evaluation code and interactive test script to aid future SimulS2ST research and application development.Comment: To appear at INTERSPEECH 202

More Continuity than Change? Re-evaluating the Contemporary Socio-economic and Housing Characteristics of Suburbs

Suburbs that developed in metropolitan Canada post-World War II have historically been depicted as homogeneous landscapes of gendered domesticity, detached housing, White middle-class nuclear families, and heavy automobile use. We find that key features of this historical popular image do in fact persist across the nation’s contemporary metropolitan landscape, particularly at the expanding fringes and in mid-sized cities near the largest metropolitan areas. Th e findings reflect suburbanization into new areas, point to enduring social exclusion, and recall the negative environmental consequences arising from suburban ways of living such as widespread automobile use and continuing sprawl. However, the analysis also points to the internal diversity thatmarks suburbanization today and to the growing presence of suburban ways of living in central areas. Our results suggest that planning policies promoting intensification and targeting social equity objectives are likely to remain ineff ective if society fails to challenge directly the political, economic and socio-cultural drivers behind the kind of suburban ways of living that fit popular imaginings of post-World War II suburbs in central areas. Our results suggest that planning policies promoting intensification and targeting social equity objectives are likely to remain ineffective if society fails to challenge directly the political, economic and socio-cultural drivers behind the kind of suburban ways of living that fit popular imaginings of post-World War II suburbs

Lack of Foraging Site Fidelity Between Years by Common Nighthawks (Chordeiles minor)

Birds in the family Caprimulgidae generally exhibit high nest site fidelity, but it is not known if fidelity extends to foraging sites, especially for Common Nighthawks (Chordeiles minor), which are otherwise one of the most studied species. Common Nighthawks are ecologically distinct from other caprimulgids, being one of the few true aerial hawking species and among the longest distance migrants in the group. We predicted these birds would exhibit fidelity between years to a foraging site in British Columbia, Canada, where they forage in large numbers on a nightly basis and the same individuals return nightly. We banded individuals and, for a subset of birds, attached transmitters programmed to activate upon return to the foraging area the next year. We estimate we marked approximately 10% of the birds foraging at the site, but did not recapture a single marked bird despite capturing potentially 50% of birds foraging at that site over the two subsequent years. Furthermore, we did not detect any of the subset of birds with radiotransmitters, indicating they did not return to the foraging site in the year following initial capture. Our data suggest low fidelity between years to a foraging site, in contrast with the published records for nesting by this species and with the general expectations for the group.National Geographic Society || Natural Sciences and Engineering Research Council of Canada || Texas Tech University || Southern Illinois Universit

Light enough to travel: migratory bats have smaller brains, but not larger hippocampi, than sedentary species

Migratory bird species have smaller brains than non-migratory species. The behavioural flexibility/migratory precursor hypothesis suggests that sedentary birds have larger brains to allow the behavioural flexibility required in a seasonally variable habitat. The energy trade-off hypothesis proposes that brains are heavy, energetically expensive and therefore, incompatible with migration. Here, we compared relative brain, neocortex and hippocampus volume between migratory and sedentary bats at the species-level and using phylogenetically independent contrasts. We found that migratory bats had relatively smaller brains and neocortices than sedentary species. Our results support the energy trade-off hypothesis because bats do not exhibit the same degree of flexibility in diet selection as sedentary birds. Our results also suggest that bat brain size differences are subtler than those found in birds, perhaps owing to bats' shorter migration distances. Conversely, we found no difference in relative hippocampus volume between migratory and sedentary species, underscoring our limited understanding of the role of the hippocampus in bats

Long-distance Movement over a Period of Days by a Female Myotis lucifugus in Newfoundland, Canada

Myotis lucifugus (Little Brown Myotis) is a regionally migrating bat, widely distributed throughout North America. Through long-term monitoring systems deployed in 2 locations in Newfoundland, Canada, we recorded the movement of an adult female of at least 375 km over a period of 4 nights. Although not the longest travel distance recorded for this species, this observation emphasizes the capabilities of Little Brown Myotis for long-distance flights, the potential connectivity among distant maternity groups, and the value of long-term monitoring programs. To fully understand the movement patterns of Little Brown Myotis, advancements in technology and greater research effort are needed.Natural Sciences and Engineering Research Council of Canada || Newfoundland and Labrador Wildlife Division || Saint Mary’s University || University of Waterlo