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abundance ofmostMalagasy frogs (Andreone&Luiselli, 2003; Andreone et al., 2008b), resulting in poor baselines fromwhich to elucidate population trends. Isolated populations of two Critically Endangered
frogs, Anodonthyla vallani and Anilany helenae, persist in Ambohitantely Special Reserve but little information is available to inform their management and any conservation interventions. Both species are endemic to a few forest frag- ments in and around Ambohitantely Special Reserve, the largest of which is 1,284 ha and is located within the pro- tected area. They are restricted to high-elevation habitats (A. vallani recorded at 1,590 m and A. helenae at 1,500 m), with an estimated extent of occurrence of 29 km2 for both species (IUCN SSC Amphibian Specialist Group, 2016, 2020). Here we provide a first estimation of population sizes and occupancy rates for both species, using acoustic surveys, and examine the ecological relationships driving these key parameters. These baseline population estimates will support establishment of conservation priorities and examination of extinction probabilities (Andreone et al., 2008b).
Study area
Ambohitantely is a Special Reserve, created in 1982, on the central plateau of Madagascar (Fig. 1a), 135 km north-east of the capital Antananarivo. The Reserve covers 5,600 ha, less than half of which is natural forest. Forest remnants are dis- tributed patchily and consist of c. 42 fragments that vary in shape and size (range 0.16–1284 ha; Fig. 1b). Together these forest fragments encompass an area of 1,627 ha (based on recent satellite data). Altitude range is 1,300–1,650 m. The subhumid climate is typical of a montane forest, with two defined seasons (wet and dry) and mean temperatures of 12.5–23 °C (Goodman et al., 2018). The area has a mean annual rainfall of 1,461 mm, of which 86% falls in the warm season (November–April).
Methods
Survey design Although A. vallani and A. helenae have been recorded in five and four fragments, respectively, in and around Ambohitantely Special Reserve (Vallan, 2000b; K.E. Mullin, unpubl. data, 2019, 2020), we collected data only in the largest fragment (1,284 ha), a forest remnant that is large enough to contain a representative number of individ- uals of both species (Vallan, 2000b). In this fragment we placed six blocks of two transects each (12 transects in total; Fig. 1). The distance between blocks was 120–1,500 m. Each transect was 300 m long and contained seven mon- itoring sites, each 50 m apart, resulting in a total of 84 sites
FIG. 1 (a) Ambohitantely Special Reserve in north-east Madagascar, with the forest fragments within the Reserve, and (b) the largest forest fragment (1,284 ha) where we conducted our study to estimate the population sizes of two Critically Endangered frogs (Anodonthyla vallani and Anilany helenae; Plate 1). Monitoring sites were in six blocks, each with two transects; each transect was 300 m long and had seven monitoring sites.
across the study area (Fig. 1). At each monitoring sitewe car- ried out a 5-minute acoustic point count survey during the night (18:00–23:00) and recorded the presence or absence of A. vallani and A. helenae (Plate 1a,b). Acoustic surveys were carried out on 8–28 December 2018, during the wet season, and each monitoring site was visited at least three times (with a 5-minute acoustic point count survey at each visit), to create a detection history. In our study area both target species could potentially be misidentified as Platypelis pollicaris (K.E. Mullin, pers. obs., 2019; Plate 1c), but they can be differentiated by an experi- enced observer (J.H. Razafindraibe, pers. obs., 2018). To en- sure that target species were being correctly identified and to control for variation in detection, a single experienced observer (JHR, who has .6 years of amphibian survey ex- perience in Madagascar) performed the acoustic surveys and species identifications. Additionally, recordings of A. vallani and A. helenae were available for comparisons in the field; JHR listened to these prior to each acoustic point count and when there was uncertainty regarding species identification. Spectrograms are available for A. vallani, A. helenae and
Oryx, 2022, 56(6), 897–903 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001034
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