High temporal resolution data reveal low bat and insect activity over managed meadows in central Europe.

Increasing agriculture and pesticide use have led to declines in insect populations and biodiversity worldwide. In addition to insect diversity, it is also important to consider insect abundance, due to the importance of insects as food for species at higher trophic levels such as bats. We monitored spatiotemporal variation in abundance of nocturnal flying insects over meadows, a common open landscape structure in central Europe, and correlated it with bat feeding activity. Our most important result was that insect abundance was almost always extremely low. This was true regardless of management intensity of the different meadows monitored. We also found no correlation of insect abundance or the presence of insect swarms with bat feeding activity. This suggests that insect abundance over meadows was too low and insect swarms too rare for bats to risk expending energy to search for them. Meadows appeared to be poor habitat for nocturnal flying insects, and of low value as a foraging habitat for bats. Our study highlights the importance of long-term monitoring of insect abundance, especially at high temporal scales to identify and protect foraging habitats. This will become increasingly important given the rapid decline of insects.

Ecosystem engineers in the extreme: The modest impact of marmots on vegetation cover and plant nitrogen and phosphorus content in a cold, extremely arid mountain environment.

Burrowing mammals strongly impact plant communities. One of the main effects is accelerating nutrient cycling and thus promoting plant growth. This mechanism is well-studied in grasslands and alpine habitats, but less is known about this phenomenon in arid, cold mountain environments. We studied ecosystem engineering by long-tailed marmots (Marmota caudata) by measuring the content of plant nitrogen and phosphorus, as well as nitrogen stable isotopes in plant biomass and marmot feces in a distance gradient up to 20 m from marmot burrows in an extremely arid glacier valley in Eastern Pamir, Tajikistan. We also captured aerial images of the area inhabited by marmots to study the spatial distribution of vegetation. There was a weak relationship between the presence of burrows and vegetation cover on soil not covered by burrow material. Burrow mounds were not colonized by plants, as opposed to other studies, where mounds are often microhabitats that enhance plant diversity. A significant increase in N and P in aboveground green plant biomass in the proximity of burrows was found in one out of six studied plant species. Contrary to our expectations, stable N isotopes did not give further insight into N routing. We assume that plant growth is strongly limited by water availability, which prevents them from utilizing the local increase in nutrients, certainly provided by marmot activity. The results are contrary to numerous studies, which showed that the role of burrowing animals as ecosystem engineers increases with increasing abiotic stress, including aridity. This shows a lack of this type of study at the end of the gradient of abiotic factors.

Energy allocation shifts from sperm production to self-maintenance at low temperatures in male bats.

The ability of animals to produce endogenous heat provides a buffer against environmental changes but also incurs high energetic costs. Especially small endothermic mammals have high energy demands. Some temperate-zone species (heterotherms) regularly use torpor, which slows down their entire metabolism but also potentially delays reproduction, to compensate for this. We used a unique experimental approach to test the consequences of extended low and high ambient temperatures on the trade-off in energy allocation to body mass maintenance, thermoregulation effort and seasonal sexual maturation in temperate zone male bats. We showed that long exposure to low ambient temperature shifts energy allocation away from sexual maturation to self-maintenance and results in a delay of sperm maturation by as much as an entire month. This effect was partially buffered by higher body mass. Heavier bats were able to afford more intensive thermoregulation and consequently speed up maturation. Interestingly, bats at constant high temperatures avoided deep torpor and matured faster than those at low temperatures, but sperm production was also slower than under natural conditions. Our results show that not only low, but also constant high ambient temperatures are detrimental during seasonal sexual maturation and the trade-off between investing into self-maintenance and fitness is a finely tuned compromise.

Spatial patterns of bat diversity overlap with woodpecker abundance.

Woodpecker diversity is usually higher in natural forests rich in dead wood and old trees than in managed ones, thus this group of birds is regarded as an indicator of forest biodiversity. Woodpeckers excavate cavities which can be subsequently used by several bird species. As a consequence, their abundance indicates high avian abundance and diversity in forests. However, woodpecker-made holes may be also important for other animals, for example, mammals but it has seldom been investigated so far. Here, we examine how well one species, the Great Spotted Woodpecker, predicts species richness, occurrence and acoustic activity of bats in Polish pine forests. In 2011 we conducted woodpecker and bat surveys at 63 point-count sites in forests that varied in terms of stand age, structure and amount of dead wood. From zero to five Great Spotted Woodpeckers at a point-count site were recorded. The total duration of the echolocation calls during a 10-min visit varied from 0 to 542 s and the number of bat species/species groups recorded during a visit ranged between zero to five. The local abundance of the woodpecker was positively correlated with bat species richness (on the verge of significance), bat occurrence and pooled bat activity. The occurrence of Eptesicus and Vespertilio bats and Nyctalus species was positively related with the abundance of the Great Spotted Woodpecker. The activity of Pipistrellus pygmaeus, Eptesicus and Vespertilio bats and a group of Myotis species was not associated with the woodpecker abundance, but echolocation calls of Nyctalus species, P. nathusii and P.pipistrellus were more often at sites with many Great Spotted Woodpeckers. Moreover, the probability of bat presence and the activity of bats was generally higher shortly after dusk and in middle of the summer than in late spring. We suggest that the observed correlations can be driven by similar roosting habitats (e.g., woodpeckers can provide breeding cavities for bats) or possibly by associated invertebrate food resources of woodpeckers and bats. The abundance of Great Spotted Woodpecker seems to be a good positive indicator of bat species richness, occurrence and activity, thus adding a group of relatively cryptic forest species that are indicated by the presence of the Great Spotted Woodpecker.

Food restriction delays seasonal sexual maturation but does not increase torpor use in male bats.

Balancing energy budgets can be challenging, especially in periods of food shortage, adverse weather conditions and increased energy demand due to reproduction. Bats have particularly high energy demands compared to other mammals and regularly use torpor to save energy. However, while torpor limits energy expenditure, it can also downregulate important processes, such as sperm production. This constraint could result in a trade-off between energy saving and future reproductive capacity. We mimicked harsh conditions by restricting food and tested the effect on changes in body mass, torpor use and seasonal sexual maturation in male parti-coloured bats (Vespertilio murinus). Food-restricted individuals managed to maintain their initial body mass, while in well-fed males, mass increased. Interestingly, despite large differences in food availability, there were only small differences in torpor patterns. However, well-fed males reached sexual maturity up to half a month earlier. Our results thus reveal a complex trade-off in resource allocation; independent of resource availability, males maintain a similar thermoregulation strategy and favour fast sexual maturation, but limited resources and low body mass moderate this latter process.

Penis size and sperm quality, are all bats grey in the dark?

Penises play a key role in sperm transport and in stimulating female genitals. This should impact post-copulatory competition, and expose penis characteristics to sexual selective pressures. Studies of male genitalia have repeatedly reported negative static allometries, which mean that, within species, large males have disproportionally small genitals when compared with smaller individuals. Males of some sperm-storing bat species may stand as an exception to such a pattern by arousing from hibernation to copulate with torpid females. The selection for large penises might take place, if a long organ provides advantages during post-copulatory competition and/or if females have evolved mechanisms allowing the choice of sire, relying on characters other than pre-copulatory traits (e.g., penis size). In this study, we measured dimensions of the erected penis in 4 sperm-storing bat species. Furthermore, we collected sperm and evaluated the link between penis dimensions and sperm velocity. Our results revealed steep allometric slopes of the erected penis length in Barbastella barbastellus and an inverse allometry of penis head width in Myotis nattereri. More detailed studies of copulatory behavior are urgently needed to explain the range of observed scaling relations. Furthermore, penis head width correlates with sperm velocity in Plecotus auritus. For this last species, we propose that penis shape might act as a marker of male fertility.