Bidirectional movements of Nathusius’ pipistrelle bats (Pipistrellus nathusii) during autumn at a major migration corridor

Migration is well documented for many species throughout the animal kingdom. Although migration is also a common behaviour in bats, it is rarely studied due to the cryptic nature of the phenomenon. Recoveries of banded individuals have shown that Nathusius' pipistrelles (Pipistrellus nathusii) can fly more than 2000 km between their summer and winter ranges in Europe, but further details of how and where they move between the endpoints of their seasonal journeys remain elusive. Here, we used three-dimensional acoustic tracking at a coastal migration corridor to elucidate the flight behaviour of Nathusius' pipistrelles during late summer. Analyzing 432 recorded flight trajectories, we show that the majority of bats followed the expected southerly direction, parallel to the coastline, on all nights, and flying at the optimal speed for long-distance travel with minimal energy expenditure. However, on one day with stronger winds, about 20 % of the bats flew in the opposite, i.e. northerly, direction. The observation of a proportion of individuals flying antiparallel to the mass of migrating conspecifics within the same movement corridor highlights that individuals may follow contrasting movement strategies at the same time and place, presumably depending on environmental conditions. We argue that it is possible for Nathusius’ pipistrelles to fly back and forth (south and north) during autumn migration, spending more time on this migration corridor than required for a straight one-way flight. This highlights the urgent need to protect migration corridors along coastlines, particularly as wind energy development continues

What a Plant Sounds Like: The Statistics of Vegetation Echoes as Received by Echolocating Bats

A critical step on the way to understanding a sensory system is the analysis of the input it receives. In this work we examine the statistics of natural complex echoes, focusing on vegetation echoes. Vegetation echoes constitute a major part of the sensory world of more than 800 species of echolocating bats and play an important role in several of their daily tasks. Our statistical analysis is based on a large collection of plant echoes acquired by a biomimetic sonar system. We explore the relation between the physical world (the structure of the plant) and the characteristics of its echo. Finally, we complete the story by analyzing the effect of the sensory processing of both the echolocation and the auditory systems on the echoes and interpret them in the light of information maximization. The echoes of all different plant species we examined share a surprisingly robust pattern that was also reproduced by a simple Poisson model of the spatial reflector arrangement. The fine differences observed between the echoes of different plant species can be explained by the spatial characteristics of the plants. The bat's emitted signal enhances the most informative spatial frequency range where the species-specific information is large. The auditory system filtering affects the echoes in a similar way, thus enhancing the most informative spatial frequency range even more. These findings suggest how the bat's sensory system could have evolved to deal with complex natural echoes

Specific recognition of CG base pairs by 2-deoxynebularine within the purine•purine•pyrimidine triple-helix motif

The sequence-specific recognition of double-helical DNA by oligodeoxyribonucleotide-directed triple-helix formation is limited mostly to purine tracts. Within the geometric constraints of the phosphate-deoxyribose position of a purine•purine•pyrimidine triple-helical structure, model building studies suggested that the deoxyribonucleoside 2'-deoxynebularine (dN) might form one specific hydrogen bond with cytosine (C) or adenine (A) of Watson-Crick cytosine-guanine (CG) or adenine-thymine (AT) base pairs. 2-Deoxynebularine (dN) was incorporated by automated methods into purine-rich oligodeoxyribonucleotides. From affinity cleavage analysis, the stabilities of base triplets within a purine.purine.pyrimidine (Pu•Pu•Py) triple helix were found to decrease in the order N.CG approximately N•AT > N•GC approximately N•TA (pH 7.4, 37 °C). Oligodeoxyribonucleotides containing two N residues were shown to bind specifically within plasmid DNA a single 15 base pair site of the human immunodeficiency virus genome containing two CG base pairs within a purine tract. This binding event occurs under physiologically relevant pH and temperature (pH 7.4, 37 °C) and demonstrates the utility of the new base. Quantitative affinity cleavage titration reveals that, in the particular sequence studied, an N•CG base triplet interaction results in a stabilization of the local triple-helical structure by 1 kcal•mol^(-1) (10 mM NaCl, 1 mM spermine tetrahydrochloride, 50 mM Tris-acetate, pH 7.4, 4 °C) compared to an A•CG base triplet mismatch

Vertical sonar beam width and scanning behavior of wild belugas (Delphinapterus leucas) in West Greenland

Echolocation signals of wild beluga whales (Delphinapterus leucas) were recorded in 2013 using a vertical, linear 16-hydrophone array at two locations in the pack ice of Baffin Bay, West Greenland. Individual whales were localized for 4:42 minutes of 1:04 hours of recordings. Clicks centered on the recording equipment (i.e. on-axis clicks) were isolated to calculate sonar parameters. We report the first sonar beam estimate of in situ recordings of wild belugas with an average -3 dB asymmetrical vertical beam width of 5.4°, showing a wider ventral beam. This narrow beam width is consistent with estimates from captive belugas; however, our results indicate that beluga sonar beams may not be symmetrical and may differ in wild and captive contexts. The mean apparent source level for on-axis clicks was 212 dB pp re 1 μPa and whales were shown to vertically scan the array from 120 meters distance. Our findings support the hypothesis that highly directional sonar beams and high source levels are an evolutionary adaptation for Arctic odontocetes to reduce unwanted surface echoes from sea ice (i.e., acoustic clutter) and effectively navigate through leads in the pack ice (e.g., find breathing holes). These results provide the first baseline beluga sonar metrics from free-ranging animals using a hydrophone array and are important for acoustic programs throughout the Arctic, particularly for acoustic classification between belugas and narwhals (Monodon monoceros).publishe