Do bats use guano and urine stains to find new roosts? Tests with three group-living bats

Abstract

Many animals use social cues to find refuges. Bats can find roosts using the echolocation and social calls of conspecifics, but they might also use scent cues, a possibility which is less studied. The entrances of bat roosts are often marked by guano and urine, providing possible scent cues. We conducted eight experiments to test whether bats use the scent of guano and urine to find potential roosts. In field experiments, we tested if Molossus molossus (velvety free-tailed bats) in Panama and Eptesicus fuscus (big brown bats) in Ohio would investigate artificial roost boxes that were scented with guano and urine more often than a paired unscented control. We did not detect any difference in flights near the scented versus unscented roosts, and we detected only one entrance into any artificial roost (scented). In six captive experiments, we tested for the attraction of Desmodus rotundus (common vampire bats) and Molossus molossus to areas scented with guano and urine, under several conditions. Results were mixed, but overall suggested that the scent of guano and urine does not act as a strong lure for the tested bat species. We suggest that further tests of olfaction-based roost choice in bats should manipulate existing scent cues on familiar roosts.

Do bats use scent cues from guano and urine to find roosts?

“…In the study by Selvanayagam and Marimuthu (1984), for instance, the male bats may have been using urine to locate their own roosting locations, to advertise their roosting locations to other bats, or both. Similarly, Brown et al (2020) appeared to have detected a strong effect of guano and urine on roost selection when bats were seeking a dark refuge, but the effect was not detected in other experiments when the entire experimental arena was dark. Some scent cues clearly do influence roost selection (Englert & Greene, 2009), but even if guano and urine is an indicator of the presence of bats at a roost, it is possible that these cues do not contain sufficient social information to be used in roost selection.…”

“…We found 119 papers on olfaction, sensory ecology, and roosting ecology in bats. Below, in chronological order, we focus on the eight studies (with 12 species from four different families) with data that could address whether bats used guano and urine cues in roost selection (Barclay et al, 1988;Brown et al, 2020;Englert & Greene, 2009;Finn, 1997;Mueller, 1966;Ruczyński & Kalko, 2007;Ruczyński et al, 2009;Selvanayagam & Marimuthu, 1984). For each species in these studies, we also summarized information about diet, social organization, roost type, and olfactory system (Table 1).…”

“…Although it is possible that the felt squares were marked with guano or urine, the source of olfactory cues used for roost choice is not clear. Brown et al (2020) investigated the use of conspecific guano and urine cues in the location of new roosts in three group-living bat species (vampire bats, Desmodus rotundus; velvety free-tailed bats, Molossus molossus; and big brown bats, Eptesicus fuscus; see Table 1). Eight experiments tested a range of situations, all of which offered individual bats the choice between a scented or unscented roosting location either in the field using roost boxes or in captivity using a dark chamber, a lit room with dark refuges, or a y-maze.…”

“…First, although bats clearly use scent in many contexts, the sparse evidence that exists suggests that the scent of guano and urine does not act as a dramatic olfactory beacon that lures bats towards roost locations to the same degree as bat calls can provide an acoustic lure (e.g., feeding buzzes, social calls, or even distress calls; Braun De Torrez et al, 2017;Carter et al, 2015;Gillam, 2007;Samoray et al, 2019). In fact, three of the studies that looked at the effect of guano and urine on roost location also looked at the effect of acoustic cues and found that while guano did not readily attract bats, acoustic cues had strong and clear effects on attracting bats to roosts (Brown et al, 2020;Ruczyński & Kalko, 2007;Ruczyński et al, 2009). This finding is consistent with the hypothesis that scent cues are not as reliable of an indicator of the immediate presence of conspecifics or the current viability of a roost, when compared to the acoustic cues of bat calls.…”

Evaluating odour and urinary sex preferences in the big brown bat (Eptesicus fuscus)

“…Male Indian short-nosed bats (Cynopterus sphinx (Vahl, 1797)) and Mexican free-tailed bats (Tadarida brasiliensis (Geoffroy, 1824) frequently mark their roosts with saliva and gular gland secretions, respectively, during the mating season to attract mates and increase mating success (Keeley and Keeley 2004;Doss et al 2016). However, guano-laced artificial roosts failed to attract more big brown bats than control roosts without guano (Brown et al 2020). To date, the ecological implications of attraction to urinary odour and the urinary patterns of E. fuscus have not been studied.…”