Mosè Nodari

IDENTIFYING BATS FROM TIME-EXPANDED RECORDINGS OF SEARCH CALLS: COMPARING CLASSIFICATION METHODS

Abstract Recording ultrasonic echolocation calls of bats using bat-detectors is often used for wide-scale monitoring in studies on bat management and conservation. In Europe, the most important legal instrument for bat conservation is the Habitat Directive (43/92/EEC), which defines various levels of species (and habitat) protection for different bat species and/or genera. Thus for most management needs, the usefulness of bat-monitoring techniques depends on the possibility to determine to species/genus. We compared the discrimination performances of 4 statistical methods applied to identify bat species from their ultrasonic echolocation calls. In 3 different areas of northern Italy, we made recordings of 20 species of bat (60% of those occurring in Italy), 17 from the family Vespertilionidae and 3 from Rhinolophidae. Calls of bats identified to species level from morphological and genetic characters were time-expanded and recorded on release. We measured 7 variables from each call, and we developed classification models through both conventional tests (multiple discriminant analysis and cluster analysis) that were based on a classical statistical approach, and through 2 nonconventional classifiers (classification and regression trees, and neural networks) that relied on generalization and fuzzy reasoning. We compared the performance of the 4 techniques using the percentage of cases classified correctly in 5 classification trials at various taxonomic levels that were characterized by an increasingly difficult identification task: (1) family level (Rhinolophidae vs. Vespertilionidae), (2) species level within genus Rhinolophus, (3) genus level within Vespertilionidae, (4) species level within genus Myotis, and (5) all species. Multiple discriminant function analysis (DFA) correctly classified marginally more cases than artificial neural networks (ANN; 74–100% against 64–100%), especially at the species level (trial 4, species of genus Myotis; trial 5, all species). Both these techniques performed better than cluster analysis or classification and regression trees, the latter reaching only 56 and 41% in Myotis species and all species trials. Artificial neural networks do not yet seem to offer a major advantage over conventional multivariate methods (e.g., DFA) for identifying bat species from their ultrasonic echolocation calls.

The strong and the hungry: bias in capture methods for mountain hares Lepus timidus

Abstract Estimating density, age and sex structure of wild populations is a key objective in wildlife management. Live trapping is frequently used to collect data on populations of small and medium-sized mammals. Ideally, sampling mammal populations by live capturing of individuals provides a random and representative sample of the target population. Trapping data may, however, be biased. We used live-capture data from mountain hares Lepus timidus in Scotland to assess sampling bias between two different capture methods. We captured hares using baited cage traps and long nets on five study areas in the Scottish Highlands. After controlling for the effects of body size, individuals caught in traps were lighter than individuals caught using long nets, suggesting that the body condition of hares differed between the capture methods. This tendency may reflect an increased risk-taking of individuals in poorer body condition and less aversion to entering traps in order to benefit from eating bait. Overall, we caught more adult hares than juveniles and more female hares than males. Our results show that estimates of density and population structure of mountain hares using live-capture data could be affected by the capture method used. We suggest that live-capture studies employ more than one capture method and test for heterogeneity in capture probability to minimise potential bias and achieve reliable estimates of population parameters.

Space use patterns of mountain hare (Lepus timidus) on the Alps.

Populations on the limits of species’ distribution can show different behavioral adaptations to strong ecological pressure than in the central part of the range. We investigated space use patterns of alpine mountain hare (Lepus timidus) at two areas on the southern edge of the species’ range. We monitored 34 hares between 2005 and 2008, estimating home range size, overlap, and site fidelity, and compared our results with space use in Scottish and North-European populations. Home ranges of mountain hares did not differ between two study areas with different habitat types. Subadult animals used larger ranges than adults and both age groups reduced home range size in autumn, a period that might be critical for hares due to changes in diet and/or high energy expenditure during the previous breeding season. Home ranges in these alpine populations were smaller than in Scandinavian populations but within the range of populations in different habitat types in Scotland. Seasonal home ranges overlapped considerably, but differed among the sexes: male–female overlap was higher than same sex (male–male and female–female) spatial overlap. Seasonal shifts of home ranges were small, and site fidelity remained high over the seasons, suggesting that resource distribution remained constant throughout the year and that the knowledge of an intensively frequented area is an important element of habitat quality. We concluded that habitat structure and availability of mates interact in affecting mountain hare space use in alpine habitats.

Recapture of ringed Eptesicus nilssonii (Chiroptera, Vespertilionidae) after 12 years: an example of high site fidelity

The vespertilionid bat Eptesicus nilssonii (Keyserling and Blasius, 1839) is the only bat species in Italy whose distribution is limited to the Alps, where it occurs above the upper tree-line (Mitchell-Jones et al. 1999, Agnelli et al. 2004). At high elevations in these mountains, populations of this species are predominant over other bats (Chirichella et al. 2003). Long-term site fidelity in bats has been mainly documented for roost sites (Chung-MacCoubrey 2003). However, re-utilisation of sites (roosts, foraging areas, etc.) by bats can be difficult to detect using surveys and high levels of effort are necessary to obtain reliable data on site fidelity. This note reports on a single recapture record for Eptesicus nilssonii, which, because of the scarcity of recapture data for ringed bats (Keen 1988, Gaisler and Chytil 2002), is relevant in increasing our knowledge of bat ecology. On 27 July 2004, we carried out bat captures using eight mist nets, over a total netting surface of 155 m2, that were opened for 4 h (21:00–01:00 h). Nets were placed at foraging sites where high foraging activity was noted (Agnelli et al. 2004). Bats were captured while hunting above pools near the Mallero stream (Pian del Lupo, Val Malenco, Sondrio province, UTM 32N 5128870E 559840N) at 1600 m a.s.l. The area was characterised by mixed subalpine conifer forests with spruce (Picea abies) and larch (Larix decidua). The subjects captured were immediately removed and held in cotton bags until the nets were closed. Species identification was carried out in the field on the basis of several identification guides available (Lanza 1959, Schober and Grimmberger 1997, Roesli and Moretti 2000). We captured a total of 24 different bats, 20 near pools and four along the stream. These included 21 Eptesicus nilssonii (3 females, 1 lactating, and 18 males), and three male Pipistrellus pipistrellus (Schreber, 1774). One male E. nillssonii had been ringed on 14 August 1992 (ring number T 070 UNIV PAVIA; Zilio personal communication), i.e., 12 years previously. The first capture occurred under street lights, 170 m away from the recapture site, in a hamlet called I Casolari in Chiareggio, Sondrio Province. Careful inspection of the bat showed no signs of damage caused by the ring, which was still freely moving on the forearm. Long-term site fidelity is well documented for roosts (Lewis 1995, Kunz and Lumsden 2003, Sgro and Wilkins 2003, Veilleux and Veilleux 2004). However, foraging site fidelity is far less known (Duchamp et al. 2004), so we believe that our observation, although based on one case, may contribute to extending this knowledge. Recently, Schmidt (2004) showed that high site fidelity is often related to an individual’s past breeding success and may have important consequences for (local) population dynamics. To the best of our knowledge, this recapture record of E. nilssonii, generally considered a sedentary species (Gerell and Rydell 2001), although movements of up to 450 km were recently recorded (Hutterer et al. 2005), is the first for this species in Italy and might indicate the occurrence of rather sedentary populations, at least in high-elevation alpine landscapes.