Bats Come Home to Roost to Home Come Bats Where Do Nighttime Prowlers Go in the Day?

ACADEMIA Where do nighttime prowlers go in the day? Chiropterology Bats Come Home to Roost Focus on WIESŁAW BOGDANOWICZ Despite the considerable ecological diver- Museum and Institute of Zoology, Warsaw sity present among bat species, a vast major- Polish Academy of Sciences ity are unable to build their own shelters and [email protected] have to make use of available roosting sites. It comes as no surprise, therefore, that these Prof. Bogdanowicz very sociable animals are most keen to popu- specializes in the ecology, IRENEUSZ RUCZYŃSKI late areas that offer plenty of feeding sites functional morphology, Mammal Research Institute, Białowieża and hideaways of various kinds. Their winter evolution, Polish Academy of Sciences roosts include all sorts of cosy subterranean and genetics of bats [email protected] nooks: most frequently caves, underground shelters, mines, and basements, although bats can also hibernate in such strange places as Because bats live clandestine lives, rodent holes or alongside hibernating snakes, many of their customs remain 0.7m under the surface. Their summer roosts understudied. Yet research has can be located in hollows and under the uncovered that their criteria bark of trees, inside rock fissures, the attics Dr Ireneusz Ruczyński in choosing homes are very similar of people’s homes, church towers, breeding studies the ecology and boxes set up for birds or bats, inside cracks in behavior of bats to those of humans: they prefer dry, bridges or under window shutters. in natural-growth forests sturdily built, warm There are more than 1,100 bat species and safe places to live in the world, 22 of which occur in Poland. Hans–Peter Stutz/8. European Hans–Peter Bat Stutz/8. Night Common noctule bats are not very dexterous in flight, and so most frequently hunt over clearings and treetops 4 4 (8) No. 2005 No. 4 (8) No. 2005 Krzysztof Skrok Simplifying things considerably, in terms of of two bat species: the common noctule bat Even though echolocation the type of roosts they inhabit bats can be (Nyctalus noctula) and the lesser noctule or constitutes bats’ main classified into two types: sylvan bats (which Leisler’s bat (Nyctalus leisleri). These two source of information almost exclusively inhabit natural roosts) types were chosen because they have much about their surroundings, and synanthropic bats (which predominantly in common: they are closely related, inhabit they have not lost live in man-made shelters). The former the forests of Eurasia and North Africa, and the ability to see group is more interesting in scientific terms, usually choose tree hollows as their repro- because it can be seen as a kind of litmus test duction sites. They form their reproductive for the changes that have taken place in our colonies in May, with the young being born environment over the past several thousand years. But most of the existing research on bats’ choice of roosts in European forests has been carried out in forested areas that have been greatly affected by man, are young, or (2004) Ruczyński I. exhibit low diversity. Our research, on the other hand, was carried out in the Białowieża Forest - a 1,500km2 area of the Polish- Belarusian borderland that has long been famous as the best-preserved deciduous and mixed forest in the European lowland. Distribution of roost trees In search of a good home occupied by colonies The research we carried out in both the of Leisler’s bats in fully-protected and managed-use portions of Białowieża Forest, located the Białowieża Forest compared the behavior using radio telemetry 5 4 (8) No. 2005 ACADEMIA Where do nighttime prowlers go in the day? Chiropterology Ireneusz Ruczyński Focus on Nets set up over rivers and ponds are the best way to catch bats in mid-June. They are migratory species that their energy expenditure. Bats then lower winter outside the Białowieża Forest. Of their body temperature, and thereby the pace course, aside from their similarities they also of their life processes. show some differences: the smaller Leisler’s bat (8-20g in body mass) is considered to be Outwitting predators closely associated with old-growth forests, The hollow occupied by a bat colony has while the larger common noctule (17-44g) to protect them not only from unfavorable also lives in considerable numbers in rela- weather conditions, but also from the numer- tively young forest stands. ous predators present in the Białowieża One might imagine that one tree hollow Forest, such as the pine marten and perhaps differs little from the next, and that when also such nest-robbers as woodpeckers and choosing where to dwell bats are more con- dormice. To protect themselves bats choose cerned with a hollow’s “floor-space” than the hollows with small exit holes, usually less conditions inside. It turns out, however, that than 4.5cm in radius - i.e. smaller than the many factors have an influence over which head of the pine martin, thereby minimizing of the available hollows are indeed chosen. A the risk of the hollow being ravaged by at dominant role here is played by weather con- least this one very dangerous type of intrud- ditions. Relatively low ambient temperatures er. At the same time, the preferred hollows and large diurnal fluctuations cause bats are located deep enough from the entrance- to choose warmer roosts, with smaller exit way that predators do not stand much chance holes. Bat homes also have to be dry and have of dragging bats out with their paws. sturdy walls. These flying mammals clearly There are also interesting differences prefer oak and ash trees, more rarely making between the two species in terms of how the use of hollows in alder, linden, hornbeam, hollows they choose were created. Common maple, and pine trees. Interestingly, these noctules most frequently employ hollows preferences varied depending on the bats’ carved out by woodpeckers, while Leisler’s physiological state: the females of both spe- bats most eagerly inhabit what are called nat- cies most frequently occupied warmer oaks ural hollows, formed by decomposition proc- when pregnant or feeding their young, yet esses in the wood. Ornithological research, in eagerly chose hollows in colder ash trees at turn, shows that the risk of losing a roost is the end of July, when their young had already greater in hollows carved out by woodpeck- taken wing. There is a logical explanation for ers than in the case of natural hollows - this this - bat pregnancy and growth proceed is probably because of the woodpeckers more rapidly in higher temperatures, but themselves, who recognize “their” hollows moving into colder hollows after the rearing and revisit them in successive years. They period allows them to significantly reduce then destroy the roosts of other species: birds 6 No. 4 (8) No. 2005 ACADEMIA Focus on Chiropterology Lesser noctules or Leisler’s bats are small and weigh some 15 grams Robert Mysłajek and bats. We surmise that common noctules, the pied flycatcher (Ficedula hypoleuca) build being a larger and more aggressive species, no more than 10 meters above ground. So are able to defend themselves from wood- why do birds choose the upper portions of peckers, while the small Leisler’s bats may trees, while birds prefer hollows lower down? be vulnerable to direct attack. For the latter, Research in the Białowieża Forest has shown the best strategy is to avoid encountering a that the higher portions of tree trunks are potential enemy in the first place. warmed by the sun more strongly, and thus the hollows there are warmer. Birds protect Higher means warmer? their chicks from heat-loss by lining their For their reproductive sites, bats choose nests with down - the temperature of the hol- hollows situated an average of 19 meters low itself is thus not as crucial as it is for bats, above the ground. This is much higher than for whom the degree of sunlight and height of birds that nest in tree hollows. By way of a hollow are of key significance. comparison, the marsh tit (Parus palustris) builds its nests at somewhat above 5 meters On the hunt on average, while the great tit (P. major) and We installed miniature transmitters (weigh- ing 0.5g) on more than 50 bats and monitored In order to take their location night after night for at least measurements of treetop several days. All of them chose roosts within hollows, researchers 6km of their hunting grounds. Nevertheless, have to employ climbing bats moved from one place to another every techniques. This gives 2.5 days on average, switching to new homes them a chance to take a across a distance of some 700m. The factors “bat’s-eye” glimpse usually seen as underlying such behavior of the Białowieża Forest include the lower risk of being discovered by predators, fewer parasites in the roosts, and greater opportunities to find roosts with a bet- ter microclimate. As long as we are talking about the hunting grounds of the bats we studied, we can mention that the diets of the two species chiefly include beetles, small flies and moths, although the proportion of beetles is somewhat smaller for Leisler’s bats than for common noctules. A more interesting European representative of the Nyctalus genus in terms Claire Duriez 7 4 (8) No. 2005 ACADEMIA Where do nighttime prowlers go in the day? Ecology The wild backwoods of the Białowieża Forest are a Focus on refuge not only for bison and wolves, but also for “winged” mammals Where do bats of the genus Nyctalus occur in the world? Definitely in those countries, at least, that commemorate them on their postage stamps! Ireneusz Ruczyński of diet is the giant noctule (Nyctalus lasiopt- Jędrzejewska, J.M.

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