Genus Micrustur

The genus Micrustur is a distinct group of six species of small to large falcons with long tails and short wings that inhabit forests from southern Mexico to Central Argentina. Little information exists on the natural habits of its members; indeed even nidification remains unknown (Brown and Amadon, Eagles, hawks and falcons of the world, I discovered a nest of the Collared Forest Falcon (M. semitorquatus) in a canopied forest (estimated to be 20-40 m high) in southwestern Guarico state, Venezuela. The nest was 12 m from the ground in the cavity of a 38-m tree (determined from a clinometer).

The Cuarico River was 200-300 m east of the nest. I found the nest around IO:00 h on 20 August 1978 and returned four hours later with three companions and tree climbing gear. I discovered one nearly fledged chick inside the nest cavity. I estimated the cavity to be about 0.50 m deep and 0.60 m wide. There were two openings into the hollow, both well sheltered from the rain and on opposite sides of the tree trunk.

One was round, about 20-30 cm in diameter and at the top of the cavity. The hole appeared to be the place where a limb had broken off and since rotted. I first located the nest by hearing the chick calling and then seeing it peering out through this hole; it was probably the entrance used by the adults. The second entrance to the cavity was a vertical slit about 30 x 20 cm. Looking into the cavity from this opening, I could see no evidence of nesting material on the floor of the cavity so presumably this species of falcon, like most others, lays its eggs in a bare scrape.

The floor of the cavity had vines growing across it while the sides of the cavity were white-washed from falcon droppings. Although I could not see any prey remains, the nest smelled heavily of decaying animal matter. When I tried to grab the chick to obtain measurements and photographs it jumped to the round entrance hole and clumsily flew about 30 m to a tree. After climbing down I looked at the chick through 10 x 50 binoculars. The primaries and rectrices were noticeably short and not fully grown. I believe that this chick was the only one because I did not hear any others calling. I first found this pair of falcons on 16 July. Although

I saw an adult, presumably the female (with an obvious brood patch) I failed to find the nest. This bird walked along horizontal tree limbs and called at me. On subsequent visits I saw little of the adults but often heard them. They uttered two calls. The first appeared to be an alarm call aimed at me and sounded like “ho, ho, ho.” The second call sounded like a single long “ho.” At times an adult gave this call and the chick returned it, but at a different pitch. On other occasions the adults gave this call back and forth to one another.

The fact that the falcons nested roughly between June and August suggests that breeding may usually occur in the wet season (April-November in Guarico). Other forest hawks such as the Roadside Hawk (Buteo mugnirostris), Crane Hawk (Gerunospiza caerulestens), and Bicolored Hawk (Accipiter bicolor) also breed in the wet season (pers. observ.).