Category Archives: Bats

Bats drink the sea

Fruit bat resting in a boat, Madang. (Anon)

Fruit bats or Flying Foxes in Seychelles (Pteropus seychellensis) are often seen skimming over the sea and this behaviour has given rise to much speculation. However, there are a lot of field observations and publications over the last 100 years of fruit bats of the genus Pteropus skimming over freshwater bodies such as rivers, lakes, reservoirs and even swimming pools . Close observations show that the bats dip their chests in the water as they fly over and then lick the water off when they roost. They can also dip their feet and then lick at these afterwards (Bergmans, 1978).

Many Pteropus species are found in coastal areas and islands and have been seen drinking salt water (Kingdon, 1974; Kock, 1972; Nelson, 1989; Ratcliffe,1961). It has been said that this is to supplement certain minerals lacking in their diet (Fenton, 2001; Kretschnann and Hayes, 2004). Animals in general actively seek salt as it appears to be a limiting factor for some especially in the tropics. As the fruits and leaves of food plants of fruit bats may be rich in water but poor in salt (Herrera, 1987; O’Brien et al, 1998) it has been assumed that they need to drink seawater. Their kidneys appear adapted to excreting salt (Iudica et al, 1994).

Certainly fruit bats in captivity are given salt solutions in addition to freshwater on the basis of these observations. When Pteropus poliocephalus and P.alecto were given a choice between freshwater and saltwater (at half the concentration of sea water), the bats drank 2 to 8 times more saltwater than freshwater (Nelson, 1989). However, when the salt solution equaled or exceeded the salt concentration of sea water, the bats drank up to 9 times as much freshwater (Barnard 2011).

Like adults in care, fruit bat pups also usually prefer salt water to fresh (Tolga Bat Hospital). At the Tolga Bat Hospital in Australia 1 teaspoon of sea salt (ground up) is mixed with 1 litre of water.

Do the bats drink directly from the sea or do they dip their breasts or chests to lick the salt later? Observations of 3 species of Pteropus in New Guinea showed that they dip their muzzles in the water (Iudica and Bonaccorso, 2003). An observer in Seychelles has noted that Pteropus seychellensis dips its breast (Gerlach, 2003). This observer attributes this behavior to bats trying to rid themselves of parasites.

Mr. R.C. Wood, a naturalist living on Cerf Island  off the main island of Mahe in the 1950’s, observed some 60 to 100 fruit bats wetting their abdomen and feet (Wood, unpublished notes). The process has been dubbed “body-wetting” and has been observed in the Comorian sub-species  (Pteropus seychellensis comorensis) although  it is attributed to thermoregulatory functions (Stobbs 1994). It may be that the bats lick  the salt off their abdomens and feet when at rest and out of sight of observers.

Pteropus vampyrus in the Philippines regularly body-dips in the ocean presumably  to obtain sodium during later grooming  (Stier 2003). This particular study suggests that the behaviour may be integral to the life of the species since the ocean dipping provides the bats with salts, and further, “that this is a critical resource that limits the distribution of some species” (ibid).

Although skimming over the sea may be a risky strategy (Gerlach, 2003) “..flying foxes, often island inhabitants, may have to fly long distances to obtain food. A forced landing or a foray over water to collect fruit which has dropped and floated there may necessitate an unexpected swim. Photographs of the flying fox, Pteropus giganteus, show the animal actually swimming, using its wings and feet to reach land rather than floating or paddling.” (Encyclopedia Smithsonian, 1980). The Australian Spectacled Fruit Bat (Pteropus conspicillatus) risks being caught by saltwater crocodiles (Crocodylus porosus) whilst drinking seawater (Nelson, 1989).

To prove without doubt that fruit bats really need salt for their metabolic balance, one may need “…to demonstrate that species of Pteropus can produce a hypotonic urine while able to conserve salts when fed on a water-rich and salt-poor diets, and alternatively would also be capable of producing hypertonic urine when fed on a water-rich, salt-rich diet”. (Iudica and Bonaccorso, 2003)

Nirmal Shah

Edited 11.4.2012

Refs.:

Bergmans, W. 1978. Review of drinking behaviour of African fruit bats (Mammalia: Megachiroptera). Bull. Carnegie Mus. nat. Hist. 6: 20–25.

Barnard. S.M. 2011. Diet and Feeding (from Bats in Captivity). Small Mammal Mail – Bi-Annual Newsletter of CCINSA & RISCINSA. 3 (2): 17

Encyclopedia Smithsonian. 1980. Bat facts. www.si.edu/Encyclopedia_SI/nmnh/batfacts.htm

Fenton, M. 2001. Bats. Checkmark Books, Revised Edition. New York, NY.

Gerlach, J. 2003. Sea-skimming by Seychelles fruit bats. Phelsuma. 11. 2003: 80.

Hall, L. 1983. Spectacled flying fox. In R. Strahan (ed.). The Mammals of Australia, Reed Books, Chatswood, 282.

Iudica, C.A and F.J. Bonaccorso 2003. Anecdotal observations of seawater ingestion by flying foxes of the genus Pteropus (Chiroptera: Pteropodidae). Mammalia. 67(3): 455-458.

Iudica, C.A, F.J. Bonaccorso, and G. Richard. 1994. Sea water ingestion in Pteropus hypomelanus. Bat Research News. 35(4):102 (Abstr.).

Kingdon, J. 1974. East African mammals. An atlas of evolution in Africa. II, A (insectivores and bats). Academic Press, London and New York.

Kock, D. 1972. Fruit-bats and bat-flowers. Bull. E. Afr. nat. Hist. Soc. 1972:123–126.

Kretschnann, K and R.L. Hayes. 2004. Old world fruit bats- Pteropus 1. http://www.Jiffynotes.com/a_study_guides/book_notes/grze_13/grze_13_00825.html

Nelson, J.E. 1989. Pteropodidae. In Walton, D.W. and B.J. Richardson (eds.). Fauna of Australia, Vol. 1B. Australian Government Publishing Service, Canberra, ACT, Australia. 852–856.

O’Brien, T.G, M.F. Kinnard, E.S. Dierenfeld, N.L. Conklin, R.W. Wrangham and S.C. Silver. 1998. What’s so special about figs? Nature. 292:668.

Ratcliffe, F.N. 1961. Flying foxes drinking sea water Journal of Mammalogy. 42: 252–252.

Stiers, S.C. 2003. Dietary habits of two threatened co-roosting Flying Foxes (Megachiroptera), Subic Bay, Philippines. Unpublished MSc Thesis. University of Montana, USA.

Stobbs, R.E.1994. Piscivory in the Comoro Islands flying fox Pteropus seychellensis comorensis – A refutation . South African Journal of Science.  90 (5): 264-265.

Tolga Bat Hospital, Australia. http://www.tolgabathospital.org/hospital_orphans.htm

 

Bat monitoring update

terence-studying-insects

If looking at this picture you think that Terence is moonlighting at another job, possibly at a lab, then you are forgiven. In fact this is our office and Terence is looking at slides of insects retrieved from recently laid insect traps around the roosts occupied by the endangered Seychelles sheath-tailed bat. The traps were set up to collect insects within foraging and non foraging areas of the bat in order to help us study  insect density and diversity.

insects

Terence is counting and grouping insects into families. The study is part of Nature Seychelles’ monitoring of the remaining roosts – with 32 individuals – of the Seychelles sheath-tailed bat on Mahe.  Apart from keeping a tally of the numbers at the roosts on Mahe, Nature Seychelles’ is keen to uncover information about food abundance. The bat is insectivorous and a past project  had identified food shortages as a possible reason for the decline in numbers. Although the study doesn’t pin point exactly what the bat eats, it helps to show what is present around the roosts.

malaise-trap

The malaise traps were laid in the beach and woodland areas but with similar vegetation. Ian, setting up the trap here, is one of the Nature Seychelles team working on the project. We will be sharing more information on the progress of study.

Seychelles Sheath-tailed Bat monitoring at Baie Lazare

On July 15, 2009 I accompanied Terence for a monitoring exercise for the Seychelles Sheath-tailed bat Coleura seychellensis carried out by Nature Seychelles at Baie Lazare, Mahe.

Baie Lazare has one of three roosts on Mahe occupied by the endemic and very rare Seychelles Sheath-tailed Bat. So rare is the bat and so limited its range that it has been listed as Critically Endangered on the IUCN Red List, and is considered close to extinction. The bat is also listed by EDGE (the edge of existence programme), the global conservation initiative which focuses on threatened and unique species.

seychelles-sheath-tailed-bat

The Seychelles Sheath-tailed bat was once abundant on Praslin, La Digue, Mahé and Silhouette. It suffered a dramatic decline during the mid-late 20th Century. The exact cause of the population decline is unknown, but it’s been linked to habitat destruction, human disturbance, decline in insect density, and possible predation by barn owls. Recent studies failed to detect any bats at previously known roosting sites on the islands of La Digue and Praslin, and the species is now thought to be extinct on both islands. This bat is now only known to roost on Mahe and Silhouette, with an estimated 50-100 individuals believed to exist. Past records show 32 individuals at La Passe on Silhouette, and 36 individuals at three roosts on Mahé: Cap Ternay, Baie Lazare, and Anse Major.

The monitoring is being done with the help of two volunteers and on this day we were accompanied by Ian Valmont.  Ian and the others have been recording dusk emergence of individuals at the roosts on Mahe. We sit outside the roost where we can see bats emerge. Ian and Terence are carrying ultrasonic detectors (Bat box) set to 37 kHz to detect when a bat is approaching. However, the counts are based on actual visuals of the bats. At this roost, 7 individuals have been recorded and all were seen on this day. Other observations on  the bats behavior and the status of the habitat are also recorded.

The bats are difficult to photograph at emergence as they fly past rather fast. My amateur skills produced very poor quality video from our digital camera. I am hoping that at the next monitoring I will be more successful. However we did manage to record some audio files on Terence’s phone picked up by the “Bat box” as they emerged (Terence is photographed here climbing to the cave with Ian Valmont, carrying the bat detector). I have uploaded it here for your listening pleasure.

seychelles-sheath-tailed-bat

Very little is known of the bat’s status and ecology, so this monitoring, part of a project that started in 2006, helps to contribute to existing data and  identify threats to its continued existence. The threat to the bats is real and present due to its unprotected status and the fact that it relies on coastal habitats which have come under intense pressure from housing and tourism development on both Mahé and Silhouette.

Find more information on the bat at EDGE