112 L. D. Martin et al.


TABLE 1 Summary of transects surveyed, including predominant habitat type, whether the transect was within the boundaries of Lokobe National Park (Nosy Be, north-western Madagascar; Fig. 1), transect length, number of times the transect was surveyed, total survey effort (L), total number of Microcebus mamiratra detected (n) and encounter rate (n/L).


Transect ID


T1 T2 T3 T4 T5 T6 T7 T8


T91 T10 T11


T12 T13 T14 T15 T16


Total 1Not surveyed after placement because of safety concerns. Predominant habitat type


Secondary/degraded forest and plantation Secondary/degraded forest and plantation Plantation Plantation


Secondary/degraded forest and plantation Secondary/degraded forest and plantation Secondary/degraded forest and plantation Secondary/degraded forest Secondary/degraded forest


Secondary/degraded forest and plantation


Primary forest, secondary/degraded forest and plantation


Within Lokobe National Park boundaries?


No No No No No No No No No No No


Primary forest and secondary/degraded forest Yes Primary forest Primary forest


Yes No


Primary forest and secondary/degraded forest No Secondary/degraded forest and plantation


No


Length (m)


961 773 855 845 792 805 925 775


1,125 717


633 684 838 713


Number of times surveyed


2 5 3 2 5 5 4 4


780 NA 812


5 4


3 3 3 5 4


L (km) nn/L 1.92


3.87 2.57 1.69 3.96 4.03 3.70 3.10


0 0.00 26 6.73 3 1.17 0 0.00 3 0.76 19 4.72 17 4.59 0 0.00


NA NA NA 4.06 4.50


2.15 1.90 2.05 4.19 2.85


46.53


1 0.25 7 1.56


3 1.39 2 1.05 3 1.46 7 1.67 1 0.35 92 1.98


behaviour (Dausmann & Warnecke, 2016), hence there should be no torpor-related availability bias (Hending et al., 2023).


Data analysis: distance software


We used theconventionaldistancesamplingenginein Distance to estimate M. mamiratra density and abundance. We pooled individual surveys and detections for each transect line, and recorded effort as line length multiplied by the num- ber of times the line was surveyed (Buckland et al., 2008).We plotted histograms of the perpendicular distances as part of an exploratory data analysis phase. We then grouped distance data into suitable distance cut points for analysis and right- truncated 10% to remove outliers and facilitate modelling (Buckland et al., 2001;Thomasetal., 2010). We then fitted the following model and adjustment combinations: uniform key function with cosine series expansion, half-normal key function with cosine and Hermite polynomial series expan- sion, and hazard-rate key function with simple polynomial series expansion. We visually assessed the candidate models andcomparedthemusing χ2 goodness-of-fit tests and the Akaike information criterion (Akaike, 1973).


Analysis of habitat on Nosy Be


The geographical range maps in the IUCN Red Lists are minimum convex polygons of the extent of occurrence of


a species and not necessarily its area of occupancy, and as a result could include areas of unsuitable habitat (e.g. non- forest, villages; Schwitzer et al., 2014). We therefore esti- mated forest cover within the extent of occurrence of M. ma- miratra on Nosy Be using Global ForestWatch (2023), and we used this forested area as a proxy for suitable mouse lemur habitat in our abundance extrapolation. Forest cover was calculated as the tree cover extent in 2000 (.30% canopy density; Hansen et al., 2013; see also Estrada et al., 2018; Mekonnen et al., 2020; Markolf et al., 2022) within the range data shapefile obtained from the IUCN Red List (Blanco et al., 2020) plus or minus net tree cover change during 2000–2022 (Potapov et al., 2022).


Results


We recorded 92 M. mamiratra detections in a total survey effort of 46.5 km (Table 1). This exceeds the recommended minimum sample size of 60–80 detections (Buckland et al., 2001).


Since 2000,c. 14.5 km2 (28%) of forest cover has been


lost within the range of M. mamiratra on Nosy Be. We estimate that 37.3 km2 of forest cover remains, an area similar to the maximum area of occupancy of the species on the island. Our distance analyses generated amean density estimate


of 125.1 individuals/km2 (95%CI 65.3–239.5, coefficient of variation 0.32). The half-normal key function with cosine


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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