The Chestnut-crowned Gnateater (Conopophaga castaneiceps), an interesting but little-known member of the Formicariidae (formerly Conopophagidae, see Ames et al. 1968) lives in cool humid mountain forests from Colombia south through eastern Peru. Retiring of habit, nothing has been recorded about its biology. I made the following observations during 1972 and 1973 in the Rio Anchicaya Valley (3"32' N, 76"48' W) on the Pacific Andean slope of Colombia. Chestnut-crowned Gnateaters are plump, dark gray birds with long pale bluish legs and a silvery white post-ocular stripe ending in a tiny tuft. The short tail is carried depressed. Live weights of six birds were 24-30 g (mean 26.8) and measurements were, culmen 11-12 mm (mean 11.7), tarsus 27.5-33 mm (mean 30.2), and wing 67-72 mm (mean 70.5). Only two of the six birds showed wing molt, a male on 24 September and a female on 17 October. The latter, identifiable by its color band, was observed nesting the following January-March. Capture dates for the four non-molting birds-10 May, 9 July, 17 October, and 19 December-suggest no molt pattern. These birds are probably most abundant at elevations of 1000 m and above on the Pacific slope but I frequently found them as low as 680 m in the Anchicaya Valley. Willis (1966) described some of the phytographic features of this foggy, rain-drenched area. Treefalls and a sharply tiered staircase-like canopy permit light to reach the forest floor in many places, resulting in a dense undergrowth of aroids, heliconias, and vines crowding upward around fallen mossy logs and boulders. In other regions, the Chestnut-crowned Gnateater also occurs in more open undergrowth forests; however, "typical" habitat for this species as well as several gnateaters of the Amazon lowlands usually includes older treefalls surrounded by tall saplings or dense second growth (Willis, pers. comm.). Chestnut-crowned Gnateaters appear to show alarm by wing-flicking, uttering a raspy call, and peering intently at the observer, often at close range. When startled by an observer, they may bound up from a low concealed perch to cling adroitly to nearly vertical branches in full view. When alarmed they do not tail-pound or tail-flick in the manner of many antbirds (for a discussion of these terms see Willis 1967). Adults forage singly or in pairs, are relatively sedentary, and are hesitant to cross trails if the clearings are more than 8-10 m. Twenty-four sightings of two banded birds representing two mated pairs were recorded between October 1972 and May 1973. From these data I learned that the maximum width of the foraging area was about 240 m along a plane horizontal to the slope. The foraging zone is low in the undergrowth. Of 48 prey-capture heights recorded, 6 were on the ground, 10 between 0.1 and 0.8 m up, 20 between 0.8-1.5 m, 9 between 1.5-2.5 m, 3 between 2.5-4.0 m, and 1 above 4 m. For 27 foraging perch diameters recorded, 9 were < 1.0 cm, 12 were from 1.0-5.0 cm and 6 were > 5.0 cm. Typically gnateaters choose low sloping stems of aroids or heliconias...
