Survival of reintroduced pygmy slow loris Nycticebus pygmaeus in South Vietnam

Abstract

From 2009 to 2012 thirteen wild-born pygmy slow lorises Nycticebus pygmaeus (in this paper referred to as pygmy lorises), confiscated from illegal trade, were radio-collared and released into secondary forest in South Vietnam. Pygmy lorises were monitored until death, recapture, or loss of collar; the longest monitoring period was 73 d. The mean (±SD) distances between consecutive sleeping sites were recorded for 324 consecutive days and averaged 122 ± 108.0 m. Mean distances between sleeping sites for males and females were similar at 110.7 ± 92.6 m for males and 128.8 ± 116.7 m for females, with the greatest distance covered by a female (793 m). Mean height of the sleeping sites was 8.54 ± 4.46 m (n = 60), in trees with a mean diameter at breast height of 75.2 ± 58.4 cm (n = 225). Mean height of the trees where lorises slept was 20.2 ± 9.0 m (n = 230). The pygmy lorises slept mostly in the >8 m band, the area of highest tree connectivity. Of the pygmy lorises studied 38% (5/13) were found dead, 7% (1/13) were returned to captivity due to severe loss of condition and for 23% (3/13) the outcome is unknown due to early collar loss. Causes of death included hyperthermia and natural predation. The remaining 30% (4/13), 2 males and 2 females, were in good condition when last tracked before premature collar drop-off, up to 73 d after release. From this limited data set, a 'soft' release, wet season release and consideration of predator density at the release site are recommendations for increasing chances of survival.