Montserrat Bats

Blown in, Blown off, and Blown up: the Bats of Montserrat, BWI.

Scott C. Pedersen

University of Washington, Seattle, WA.; University of Nebraska State Museum, Lincoln, NE

When one thinks of Montserrat, the last thing that comes into most peoples minds are the bats that might live on the island. Yet, to a scientist, bats are incredibly important animals as they are important pollinators, indispensable seed dispersal agents, and critical elements in an island's healthy ecosystem. As such, the bats are absolutely critical to Montserrat's recovery in the years to come and will continue to receive a great deal of attention from scientists. Six surveys (1894, Thomas; 1978, Jones & Baker; 1984, Pierson et al.; 1994, Pedersen; 1995, Morton & Fawcett; 1997, Pedersen) have established a considerable data base that includes nearly 1200 captures of ten species from 45 locations [Fruit bats: M. plethodon, S. thomasi, C. improvisum, A. jamaicensis, A. nichollsi, B. cavernarum; Insectivores: N. stramineus, T. brasiliensis, M. molossus; Carnivores: N. leporinus].

Effects of Hurricane Hugo, 1989

The bat population on Montserrat was devastated by Hurricane Hugo and suffered a 90% decrease in numbers (estimated by bat
captures per net-night. The bat species that were hardest hit on island were those that lived in trees, or fed on fruit from "fragile" trees that had been destroyed by Hugo. The ecosystem and fauna of Puerto Rico was also heavily damaged by Hurricane Hugo. As on Puerto Rico, bats on Montserrat that were able to utilize alternative roosts and alternative food items (Omnivores) survived and recovered much more quickly than their more specialized cousins (e.g., small frugivores - fruit-eating bats). Of interest, omnivorous birds followed this same trend after Hugo, an important observation that underlines the importance of plasticity in habitat and diet in all animals that live in the hurricane belt. Since Hugo, Chiroderma improvisum (an endemic fruit bat) has not been collected on Montserrat. It would of great interest to know if this species was
blown off the island or still exists as very rare species on Montserrat.

Effects of Volcanic activity, 1995+

The bat population on Montserrat has been further devastated by the continuing eruption of the Soufriere Hills volcano. Pyroclastic flows have destroyed major roost sites and foraging habitat for bats. The bat population had not shown signs of recovery from Hugo's devastation in 1995 when the volcano first erupted and things have gotten much worse. The results of the most recent census (July 1997) showed that the bats were exhibiting obvious signs of stress (notably mange and extremely high external parasite loads) that had been at insignificant levels before the eruptions began. Four species are of immediate concern because of the continuing destruction of roosts and habitat.

1) Natalus stramineus (Funnel-eared bat) is a delicate insectivorous bat that has been captured only in the Belham Valley. It is extremely difficult to catch and it's population may well be underestimated. Nevertheless, their only known maternity colony lies at the floor of the Belham Valley and is in clear danger of being destroyed.

2) A small population of Noctilio leporinus (the "Fishing bat"; see photographs) lives along the Belham river and is at great risk because the heavy silt load carried by the Belham Valley River has directly impacted/destroyed their major food sources: minnows, tadpoles, and aquatic insects. With continued destruction of this drainage and it's important roost sites, this population will be lost from Montserrat altogether.

3) A large roost used predominantly by Brachyphylla cavernarum (a large fruit bat) was destroyed by pyroclastic flows in 1996. The mass northward migration of people, livestock, and wildlife (including bats!) has generated severe problems: limited housing, crowding, poor sanitation, social disruption, limited resources, destruction/clearing of land, etc.. Resultant stress on Montserrat's bats, especially this cave-roosting species, may explain why 90% of
Brachyphylla captured in 1997 exhibited mange and all animals carried large numbers of external parasites (Macronyssid mites, Argasid ticks, and Streblid batflies). It is absolutely critical that the remaining caves at the north end of the island are protected.

4) I was very excited in 1994 when I reported the presence of a new species of bat on the island of Montserrat - the medium- sized fruit bat Sturnira thomasi. Two studies later and a tremendous amount of effort have failed to turn up further examples of this rare species. If this species of bat is in fact gone, then Montserrat has lost two endemic species of bat in less than 10 years time. Given that there have been only ten species of bat described on this island, the
loss of two endemics is a frightening blow to the islands biodiversity!

It will be of the greatest importance to monitor the bats on Montserrat over the next decade to see:
1) if population levels and composition of the community recover or continue to decrease,
2) how these recovery events will be distributed across the island, and
3) to what extent the frugivorous bats contribute to the reforestation of devastated areas.

If you have further questions, please feel free to contact Scott C. Pedersen, Ph.D., Department of Orthodontics, University of Washington, Seattle, 98195, USA. 206-543-5798,
bathead@u.washington.edu.

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Both photographs
are of Noctiolio leporinus,
the fishing bat.