Foraging activity of the free-tailed bat Molossus molossus (Chiroptera; Molossidae) in southeastern Brazil

Abstract

Sunset and sunrise regulate the activities of most studied bat species. To verify patterns of foraging activity, 29 bat sampling nights were carried out over a dam in Rio de Janeiro city, which resulted in 363 hours with 730 captures, representing 13 species of insectivorous bats. Molossus molossus constituted the bulk of the captures (79.9%) and was present in 82.8% of the sampling nights. This bat species exhibited crepuscular and nocturnal activity (from -6 minutes to 900 minutes after the time of sunset). A bimodal activity pattern was observed, and two non-overlapping capture peaks. The first peak lasted from 6 minutes before sunset to 420 minutes after sunset. The second peak began at 564 minutes after sunset and ended just after sunrise. The first capture peak was observed in 75.9% of the nights, and the second peak in 62.1% of the nights. The time of the first capture exhibited a positive linear relationship with sunset and the time of the last capture, a positive linear relationship with sunrise. The existence of a relationship between night length and the difference between first and last captures of each night shows that M. molossus has longer activity the longer the night, showing a seasonal variation in the activity period. Keywords Material and MethodsBetween 1993 and 1999, bat samplings with nets set over a dam were carried out during non-consecutive nights in an urban park "Parque da Gávea" (23° 58' 68.7" S and 43° 14' 54.3" W). This dike has an area of 400 m 2 and neighbors a secondary forest. For further characteristics of the site see Esbérard (2003) and Esbérard and Bergallo (2008). Each night from seven to ten mist nets (7 × 2.5 m, mesh of 20 mm) were set at least one hour before sunset, and remained opened until one hour after sunrise.The exact capture time of each individual was recorded, by using radio communicators operated by the team members who remained next to the nets. Bats were measured, weighed, marked with a tattoo pincher with green India ink, and released from 30 to 60 minutes after capture. Recaptures on the same night were not considered in this analysis.The capture time of each individual was converted in minutes after sunset and minutes before sunrise. Sunset and sunrise local times were obtained with the software Moonphase Southern Hemisphere 3.0. In order to analyse capture frequency, data were grouped in 30 categories in relation to sunset, starting at -30 and finishing at 900 minutes. A linear regression between capture time and local sunset and sunrise times was estimated in Systat 8.0, considering, respectively, the first and the last capture of each night. To test whether M. molossus has a longer activity period during longer nights, a linear regression between the total in minutes from sunset to sunrise and the difference between the first and the last capture of each night was estimated. ResultsSamplings were carried out at 29 nights (total of 363 hours), which resulted in 730 captures of 13 different species of insectivorous bats. Molossus molossus repre...

High manoeuvring costs force narrow-winged molossid bats to forage in open space

“…This dusk peak in prey availability may drive molossids to forage predominantly during the early night, sometimes for only a half an hour interval (e.g. Esbérard and Bergallo 2010;Dechmann et al 2010Dechmann et al , 2011. As a consequence, resting bats may reduce their energy expenditure by remaining inactive or by entering torpor during the remaining hours of the day.…”

“…Among Chiroptera, molossid species belong to the fastest flying bats that cover long distances while hunting for high-flying insects (Vaughan 1986;McCracken et al 2008). Members of this family (Molossidae) hunt predominantly moths and beetles in open spaces such as above the forest canopy (Fenton 1972;Freeman 1979;Esbérard and Bergallo 2010;Jung and Kalko 2011). Molossids have long and narrow wings, and an above average AR and wing loading compared to bats of similar body mass from most other taxonomic families (Norberg and Rayner 1987).…”

Seasonal variation of energy reserves and reproduction in neotropical free-tailed bats Molossus molossus (Chiroptera: Molossidae)

“…The insectivorous bat Molossus molossus consumes a high amount of protein and acts as controller of insect populations preying large amounts each night in the first hours of the night (Esbérard and Bergallo, 2010), playing an important role in the ecological balance. This species has a reproductive cycle defined as seasonal polyestrous by Fabian and Marques (1989) in northeastern Brazil, and as seasonal monoestral by Pacheco (2001) in the southern region of the country.…”

Terrestrial locomotion imposes high metabolic requirements on bats

“…For example, bats may lack the ability for elastic energy storage during quadrupedal locomotion; a mechanism that helps rodents in reaching a high mechanical efficiency during terrestrial locomotion (Biewener et al, 1981). We are uncertain if bats were exhausted after running for ~1min at high speed but, considering that bats of the genus Molossus are capable of flying continuously for 30-60min when foraging (Esbérard and Bergallo, 2010), it seems unlikely that physiological exhaustion prevented them from continuing their sprint. Molossid bats performed well during terrestrial locomotion, yet they seem to lack the high efficiency of rodents in converting muscular work into running speed.…”