Habitat associations of the Manchurian Reed Warbler Acrocephalus tangorum wintering on the Tonle Sap floodplain and an evaluation of its conservation status

Abstract

Sixty tape playback trials and 17 net rides were used to investigate the habitat associations of Manchurian Reed Warbler Acrocephalus tangorum at what is potentially its most significant wintering site, the Tonle Sap floodplain in Cambodia. Fieldwork in March 2006 concentrated at three sites within the inundation zone during the dry season when floodwaters are at their lowest. This corresponds with the non-breeding season, when Palearctic migrant Acrocephalus warblers visit. We analysed cover of different habitat types at two scales: close to and broadly surrounding playback locations. Detections within broad habitat types differed significantly from random (c2 = 32.8, d.f = 5, P < 0.001) with an apparent bias towards grass habitats represented in the study area by tall ( > 1.0 m) grassland. A principal component analysis (PCA) of the proportionate abundance of different habitats within 10 m of playback locations generated just two PCA axes, correlating strongly with the abundance of grassland and wet habitat features (PCA1) and woodland and scrub (PCA2). Logistic regression with both axes as predictor variables revealed a significant effect of PCA1 (z = -2.566, P = 0.010), but no significant effect of PCA2 (z = 0.088, P = 0.419). All sites with detections had a low loading on PCA1, suggesting a strong association with grasslands. Capture rates were extremely low compared with one wintering location in Thailand, so while our study suggests the Tonle Sap is of global importance for the species, we cannot find sufficient evidence to warrant revising the species's IUCN Red List status from Vulnerable to a lower category of threat.