Seasonal Eidolon helvum colony at Kasanka National Park, Zambia
Excerpt from Peel et al (2017)
Location:
The largest known colony of E. helvum roosts in a 0.4km2 patch of ‘mushitu’ evergreen swamp forest in Kasanka National Park in Central Zambia.
Population size and migration:
The site is empty for most of the year, is populated rapidly from late-October each year, and persists for 2 ½ months. The arrival and departure dates are remarkably consistent annually, and coincide with peak fruit production in the region (Richter and Cumming, 2006). The peak population size has been estimated at between 1.5 million (Sørensen and Halberg, 2001) and 5–10 million (Richter and Cumming, 2006) individuals, giving a density of 4–25 bats per m2. In this study, bats were observed roosting in all three canopy layers of dense vegetation, and often much lower to the ground (5–15 m) than is typically observed in urban colonies. While no further estimations of population size were performed, the population was anecdotally reported by park guards to have declined over the last decade.
Reproductive seasonality:
Almost all (68/69) females sampled here were pregnant, and the majority were in early to mid gestation (56% and 32% respectively). While no females were observed with attached juveniles from 27/11 – 3/12/2008, 5 females (7%) were in late stage of pregnancy, and one female was observed giving birth in the colony on 3/12/2008. Lack of complete synchrony in female reproductive status meant that a ‘phase’ was not estimated for this colony.
Roost structure:
A female bias (63%) was observed in bats caught by hand, in mist nets and by shooting (by another research team in the park at the time).
Bat-human interactions:
The E. helvum roost in Kasanka National Park is a tourist attraction, with tourists visiting the periphery of the colony to watch the bats fly out to feed at dusk and return to the roost at dawn. While close contact is not permitted, the sheer number of bats flying overhead still presents a risk of contact with urine and faeces. Park employees, researchers and film crews are permitted to enter the bounds of the colony, and therefore face an increased risk, however no facemasks or other personal protective equipment are routinely worn. For this, and previous research, bats were caught by hand by park employees, with a high risk of incurring bite wounds. No employees reported any clinical signs believed to be associated with bite wounds.
Refs:
Peel, A. J., J. L. N. Wood, K. S. Baker, A. C. Breed, A. de Carvalho, A. Fernndez-Loras, H. S. Gabrieli, G. Gembu, V. A. Kakengi, P. M. Kaliba, R. M. Kityo, T. Lembo, F. Esono Mba, D. Ramos, I. Rodriguez-Prieto, R. Suu-Ire, A. A. Cunningham, D. T. S. Hayman 2017 How does Africa's most hunted bat vary across the continent? Population traits of the straw-coloured fruit bat (Eidolon helvum) and its interactions with humans. Acta Chiropterologica 19(1)
http://www.bioone.org/doi/abs/10.3161/15081109ACC2017.19.1.006
Richter, H., & Cumming, G. (2006). Food availability and annual migration of the straw-colored fruit bat (Eidolon helvum). Journal of Zoology, 268(1), 35–44.
Sørensen, U., & Halberg, K. (2001). Mammoth roost of nonbreeding straw-coloured fruit bat Eidolon helvum (Kerr, 1792) in Zambia. African Journal of Ecology, 39, 213–215.
