Journal of Mammalogy, 86(4):719- 728, 2005 DIETARY HABITS OF THE WORLD’S LARGEST BATS: THE PHILIPPINE FLYING FOXES, ACERODON JUBATUS AND PTEROPUS VAMPYRUS LANENSIS Sam C. Stier* and Tammy L. M ildenstein College of Forestry and Conservation, University of Montana, Missoula, MT 59802, USA The endemic and endangered golden- crowned flying fox (Acerodon jubatus) coroosts with the much more common and widespread giant Philippine fmit bat (Pteropus vampyrus ianensis) in lowland dipterocarp forests throughout the Philippine Islands. The number of these mixed roost- colonies and the populations of flying foxes in them have declined dramatically in the last century. We used fecal analysis, interviews of bat hunters, and personal observations to describe the dietary habits of both bat species at one of the largest mixed roosts remaining, near Subic Bay, west- central Luzon. Dietary items were deemed “important” if used consistently on a seasonal basis or throughout the year, ubiquitously throughout the population, and if they were of clear nutritional value. Of the 771 droppings examined over a 2.5 -year period (1998-2000), seeds from Ficus were predominant in the droppings of both species and met these criteria, particularly hemiepiphytic species (41% of droppings of A. jubatus) and Ficus variegata (34% of droppings of P. v. ianensis and 22% of droppings of A. jubatus). Information from bat hunter interviews expanded our knowledge of the dietary habits of both bat species, and corroborated the fecal analyses and personal observations. Results from this study suggest that A. jubatus is a forest obligate, foraging on fruits and leaves from plant species restricted to lowland, mature natural forests, particularly using a small subset of hemiepiphytic and other Ficus species throughout the year. In contrast, P. v. ianensis has a broader diet, including fruits, leaves, and flowers; forages in both natural and agroforests; and uses a wider variety of fruit than does A. jubatus in natural forest habitats. A small subset of the available Ficus species also is used heavily by P. v. ianensis throughout the year. These results provide insight into the autecology and interspecific relationship of these coroosting species, as well as suggest the prospects of both species’ continued survival given changes in their habitat. Key words: Acerodon jubatus, diet, flying fox, food habits, foraging habitat, fmit bat, giant Philippine fmit bat, golden - crowned flying fox, Philippines, Pteropus vampyrus Large flying foxes (Megachiroptera, Pteropodidae; forearm precipitously in the Philippines over the last century, principally length >110 mm) are one of the most threatened groups of bats, because of the loss of habitat (Heaney et al. 1998). particularly in Southeast Asia (Mildenstein 2002). The golden - The golden -crowned flying fox was the 1 st endemic species to crowned flying fox(Acerodon jubatus) and giant Philippine fruit be described from the Philippines, in 1831 (Utzurrum 1992). In bat (Pteropus vampyrus ianensis) are the world’s largest bats. the intervening some 170 years, no dietary or ecological studies Mature adults of both species weigh nearly 1 kg or more and have have been published of the species. The only mention of dietary wingspans of up to 2 m (Ingle and Heaney 1992; Mildenstein items of the species at all comes from Utzurrum (1984; and see 2002). The golden- crowned flying fox is endemic to the Utzurrum 1995), who concluded that A. jubatus used 4 Ficus Philippine Islands and is classified as endangered; the giant species, although without quantifying this use. Methods used in Philippine fruit bat is an endemic subspecific member of a species Utzurrum’s study (1984— ejecta size and teeth and palatine that ranges throughout Southeast Asia and is considered impressions) could not distinguish between several large vulnerable (Mickleburgh et al. 1992). Colony sizes and the Philippine flying foxes (A. jubatus, P. v. ianensis, and P. numbers of roosts containing these species have declined hypomelanus), whereas mistnetting and sightings in the vicinity of fmiting trees allowed use only to be inferred. Meanwhile, dietary information onP. v. ianensis is tabular, and comes from other countries or areas (see Fujita 1991; Gould 1977; Lim Boo * Correspondent: [email protected] Liat 1966; Medway 1969; Utzunum 1984; Widmann 1996). Thus, more detailed and quantified dietary information is needed © 2005 American Society of Mammalogists to provide a clearer scientific foundation for understanding and www.mammalogy.org developing conservation strategies for these species. 719 720 JOURNAL OF MAMMALOGY Vol. 86, No. 4 from the capital city of Manila (Magdaraog 1992). The Reserve lies on the northwestem slopes of Mt. Natib (elevational range: 0 1,287- m), 20 - and is approximately 9,856 ha in size (Magdaraog 1992). Mean annual 2 0 0 km rainfall is 324.6 cm (135.3 inches— Department of the Navy 1981). The majority of the mean annual rainfall (83.4%) occurs from June to H Old (irovMh I'oresl September, with the rest falling over the remaining 8 months of the year (URS 2001). More detailed biophysical description of the study site can be found in Stier (2003) and Mildenstein (2002). The Reserve contains mangrove, beach, riparian, and lowland dipterocarp (Dipterocarpaceae) formations; the latter comprises the Republic of the Philippines majority of the area. Classic description of the lowland dipterocarp L u zo n Islan d formation can be found in Whitmore (1984; and see Richards 1952), but a reference more specihc to the study site and its peculiarities can be Subic Bay Forest — > found in Whitford (1906, 1911). Whitford (1911) subdivides the Reserve lowland dipterocarp formation in the Philippines into several types, '5 f placing much of the study area into the Lauan Apitong- type, a dipterocarp formation extending from sea level to 300M00 m, distinguished climatically by its relatively long dry season, and sub­ sequently differing both floristically and structurally from other dipterocarp formations. Floristically, apitong {Dipterocarpus grandi- florus) codominates the dipterocarp component of this forest type with white lauan {Shorea contorta), along with many species adapted to seasonally dry conditions and often exhibiting deciduous habits (e.g., 10 _ kupang [Parkia roxburghii}). Structurally, this is the most open of the dipterocarp subtypes, and large trees are often interspersed with groves of bamboos (Graminae), creating a savannah or parklike matrix (Whitford 1906). The study area had been selectively logged during the United States Navy’s use of the area from 1898 to 1991 (see Stier 2003 for further historical description). Fecal collection and analysis.—Given the short food passage­ rates of flying foxes (Wolton et al. 1982), we assumed that each bat voided its last meal once, so that each dropping collected at the day roost represented the food choice of a different individual. Observation of bats at the roost appeared to support this assumption. However, fecal material dropped on collection plastic may result in a multiple, rather than a single, deposit (e.g., from splattered material or discontinuous deposition). To address this, collection of splatters was minimized by Fig. 1 .— ^Location of study site within the Philippine archipelago not collecting fecal matter immediately adjacent (within 5 cm) to (modihed from Wildlife Conservation Society of the Philippines a collected dropping having the same appearance. Shilton et al. (1999) [1997]). found that Old World fruit bats could have extended gut retention times (e.g., >12 h; see also Okon 1974:36) and A. jubatus was at We studied the diets of these species at Subic Bay, times observed in this study to defecate after 3 h at the roost after night foraging. However, this was rare, and droppings defecated after an Philippines, in an effort to better understand the autecology extended period, which have a characteristically dark color (Shilton and interspecific relationship between these 2 similarly sized, et al. 1999; see also Okon 1974:36), were rarely encountered on coroosting bats and to develop information useful for their collection plastic sheets. conservation (see Stier 2003). Foraging habitat is one of the Despite roosting together in the same colony, A. jubatus and P. v. most fundamental limiting resources for wildlife, including for Ianensis generally select separate trees or distinct areas within a shared bats (Findley 1993). This is specifically suggested by the fact canopy to roost (S. Stier, in litt.), making it possible to collect their that there is a strong, positive relationship found throughout the droppings separately with adequate observation of a roost and careful Philippines between the area of natural forest remaining and placement of collection plastic. Droppings of each bat species were colony sizes ofA. jubatus and P. v. Ianensis (T. Mildenstein, collected undemeath their respective roosting areas and stored S. C. Stier, and A. Cariho, in litt.). Less clear is why, within individually for processing. Droppings were rinsed individually these mixed- roost colonies, population sizes of P. v. Ianensis through a 0.3-mm mesh and the material remaining on the mesh was characteristically dominate those of A. Jubatus by 10 to 1 (T. examined through a magnifying glass. We described this material by its botanical identity (e.g., anther, insect gall, seed, funicle, or leaf Mildenstein, S. C. Stier, and A. Cariho, in litt.). fragment) and gross morphological features (e.g., size, shape, and color). M a t e r i a l s a n d M e t h o d s We compared seeds from each dropping with a reference collection, Study area.—^The Subic Bay Forest Reserve (14.45 14.51°N,­ which was assembled from fruiting trees throughout the study area 120.09- 120.22°E) is in the west-central region of the large northem (particularly Ficus species), and seeds from herbarium samples. We island of Luzon, Philippines (Fig. 1), 130 km by road and 65 km by air identihed trees from which the seeds came by using a combination August 2005 STffiR AND MILDENSTEIN— DIETS OE THE WORLD’S LARGEST BATS 721 of field guides and lexicons (Guzman et al.