Claire’s mouse lemur 111
assessments, inappropriate conservation management deci- sions or the misallocation of limited conservation funds (Elphick, 2008). Here we provide the first reliable estimates of density and
abundance for M. mamiratra using line transects, a system- atic random survey design and best-practice field protocols. Population estimates will inform future status assessments and conservation actions for this threatened primate.We pre- dict that density estimates for M. mamiratra are similar to those reported for other mouse lemur species from the dry and transitional forests of north-westMadagascar, consistent with large-scale regional patterns in mouse lemur densities (Setash et al., 2017). We also predict that encounter rates at Nosy Be are higher in unprotected, anthropogenic habitats than in protected, primary forests, consistent with general patterns in mouse lemur abundance (Hending, 2021).
Study area
Nosy Be is a 321 km2 island in the Mozambique channel to the north-west ofMadagascar, c. 12 km from the mainland. It is part of the Sambirano Domain, a transitional area be- tween the eastern wet and western dry forests (Sawyer et al., 2015). The climate is tropical with a hot, wet season during October–April and a cooler, dry season during May– September (Cutler, 1965; Andreone et al., 2005). Mean daily temperatures range from 23 °C during July–August to 28 °C during January–February (Birkinshaw, 1995), and mean annual rainfall is 2,250 mm (Andreone et al., 2005). Most of the original forest cover on Nosy Be has been con- verted to agricultural land, including rice and ylang-ylang crops (Andreone et al., 2005). The 7.4 km2 Lokobe National Park protects most of the remaining primary for- est, which is classified as low-altitude humid evergreen for- est (Hasiniaina et al., 2018). The Park is surrounded by a mosaic of secondary and degraded forest, crop plantations and small villages (Birkinshaw, 1995; Tinsman et al., 2022). Elevation across Nosy Be is 0–430 m, with the primary for- ests of Lokobe National Park occupying some of the highest slopes (Tinsman et al., 2022). The black lemur Eulemur macaco and the Nosy Be or Hawks’ sportive lemur Lepilemur tymerlachsoni are the only lemurs sympatric with M. mamiratra on the island. Nosy Be has been identified as a priority area for lemur conservation (Schwitzer et al., 2013, 2014) and is also one of the most popular tourist destinations in Madagascar (Jędrusik, 2019).
Methods
Survey design and transect placement We used the survey design function in Distance 7.5 Release 2 (Thomas et al., 2010)tosuperimpose agrid ofpoints with a
randomstarting position across amap of the extent of occur- rence of M. mamiratra on Nosy Be, obtained from the most recent IUCN Red List assessment (Blanco et al., 2020). We then used the coordinates of these grid points to place a sys- tematic set of segmented parallel transect lines in and around Lokobe National Park.We placed 16 transects in the survey area (Table 1), but only surveyed 15 of these because of safety concerns at one location (small flooded areas considered unsafe for nocturnal work; T9, Fig. 1). The mean transect length was 815 m (range: 633–1,125 m), which we measured in the field with an open reel tape measure. Some transects were shorter because they crossed impassable terrain such as ravines. Transects covered areas of primary, secondary and degraded forest, and plantations both within and out- side the National Park boundaries. We cut the transects in straight lines in a north–south direction, only deviating to avoid dangerous (e.g. boulders) or inaccessible areas (e.g. paddy rice plantations) where necessary. We marked the transects with fluorescent flagging tape so that observers could identify the centreline during surveys.We then waited at least 72 h before surveying, to minimize the effects of dis- turbance from cutting the transects (Bessone et al., 2023).
Line transect surveys
Author LDM provided training to all observers on distance sampling theory (e.g. survey design, key assumptions) and field protocols (e.g. equipment use, searching behaviour) at the start of the field season. We conducted nocturnal sur- veys in the wet season during 17 February–4 April 2023. Beginning at sunset (c. 19.00), teams of 2–3 observers walked a transect in single file at amean speed of 1–2 km/h, pausing during heavy rainfall. Observers stopped to scan the survey area at regular intervals, concentrating search effort on and near the line.Weused headlamps to locate mouse lemurs by reflective eye shine and binoculars to distinguish M. mamir- atra from other wildlife. Observers would temporarily leave the transect line to confirm the identification of detections as required. For each mouse lemur detected, we recorded cluster size and perpendicular distance from the transect line on a standardized datasheet. Wemeasured perpendicu- lar distances with a laser rangefinder and paced distances ,4 m (the minimum range of the rangefinder). We re- corded detections of each mouse lemur individually (i.e. cluster size of 1), including where we detected mouse lemurs in groups of 2–3 (Buckland et al., 2001, 2010). We recorded only visual detections. We surveyed each transect 2–5 times. We regularly changed team composition to minimize between-team observer variability.Westored field data elec- tronically and verified the data daily. Although M. mamira- tra is not believed to undergo prolonged periods of torpor (Tinsman et al., 2022), we conducted our surveys outside the dry season, when mouse lemurs typically exhibit this
Oryx, 2025, 59(1), 109–118 © The Author(s), 2025. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605324000772
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