コビトトラフサギ Zebrilus undulatus

Small, dark, rarely seen heron of forest. Plumage is entirely gray-brown with fine black vermiculations; young birds sport warmer tones. Occurs at low density in swampy forest, especially along densely vegetated riverbanks and in areas with much standing water. Stays close to cover and forages deliberately, walking slowly on the ground or ambushing prey from low perches, flicking tail continuously. May freeze or fly off awkwardly when startled. Heard more often than seen; song is a muffled hoot, repeated at long intervals, usually given before dawn or at dusk. Combination of small size, dark plumage and forest habitat should clinch identification.