Colonies of some emballonurid species are easily found because these bats emit social calls audible to humans. The roosting posture of emballonurid bats is characteristic as they support their body from the surface by the thumbs of the folded wings.
The social behavior of the greater sac-winged bat can be observed easily from some distance. The mating system has been described as harem-polygynous, but recent studies using molecular genetic techniques proved that harem males father only 30% of the offspring within their harems. However, harem holders have on average a higher reproductive success than non-harem males and, therefore, males benefit from defending a group of females. The courtship of male S. bilineata includes visual, acoustic, and olfactory displays. Besides a large number of social calls that have been described for this species, males emit songs that can last for up to an hour and that include many different syllables. Songs of male S. bilin-eata are partly in the audible range of humans. In addition to singing, males also perform hovering flights during which fragrances are fanned towards roosting females. Males possess
specialized holding sacs in the front wing membrane in which the fragrances are stored. The scents emanating from wing sacs of emballonunrid bats smell differently in different species. Histological studies proved that holding sacs of male S. bilineata and other emballonurid bats do not contain any glandular tissues. Male S. bilineata actively fill fragrances into the wing sacs each afternoon during a stereotyped behavioral sequence. During the first phase, which has been interpreted as cleaning, males swallow their urine and lick the holding
sacs intensively. After approximately 10-20 minutes of cleaning, males rest for a few minutes and then switch to a second phase. During the second phase, males press their chin onto the penis and deposit a small droplet at their chin. Afterwards, males smear this droplet into one of the holding sacs with a sideward movement of the head. This secretion probably originates from the preputial glands. Additional droplets of the gular gland are also added to the holding sacs. When transferring genital and gular secretions to the holding sacs, males alternate between the two sacs, thus refilling almost equal amounts of fragrances into both wing sacs. The second phase of perfume-blending can last up to 20-30 minutes. It is unknown if other emballonurid species with wing sacs in the male sex show a similar behavior.
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