Sharpbills

(Oxyruncidae)

Class Aves

Order Passeriformes

Suborder Tyranni (Suboscines)

Family Oxyruncidae

Thumbnail description
Smallish tyrannid with spotted plumage and sharp bill

Size
6–7 in (15.2–17.8 cm); 1.6 oz (44 g)

Number of genera, species
1 genus; 1 species

Habitat
Humid montane forests

Conservation status
Unknown

Distribution
Tropical Central and South America

Evolution and systematics

The exact affinities of the sharpbill (Oxyruncus cristatus) have been in dispute since the genus Oxyruncus was first described in 1820. Since the late nineteenth century most authors have given the sharpbill family status, despite its widely scattered distribution. Sharpbills are obviously related to the tyrannid passerines, particularly the tyrant flycatchers, cotingas, and manakins. However, the sharpbills' exact relations with these groups remain unclear.

In the 1980s, genetic comparisons seemed to indicate that sharpbills are cotingas and also are closely related to tityras and becards. However, for the purposes of this discussion the sharpbills are treated as a separate family (Oxyruncidae) within the Passeriformes as per Peters checklist.

This monotypic family has been divided into five races, differentiated slightly by color and size, but mainly by their distribution. Oxyruncus cristatus frater, the Costa Rican sharp-bill, ranges from northeastern Costa Rica to western Panama, where it is known by its Spanish name, Pico Agudo. O. c. brooksi is found in the Darien region of Panama. O. c. hypoglaucus inhabits the highlands of southern Venezuela, Guyana, and Suriname. O. c. cristatus and O. c. tocantinsi are both found in Brazil (the latter may be synonymous with O.c. hypoglaucus).

Physical characteristics

Sharpbills are small, stocky birds with a muted but distinctive plumage. The back, scapulars, and rump are olive green. The sides and flanks shade from dull white to greenish yellow. Tear-shape spots fade from buffy on the breast (except in the center of the abdomen, where they are absent) to smaller, darker, and denser on the head. The wings are blackish, with two yellowish bars. The tail is blackish, and the short, stout feet are a dull gray.

The sharpbill's head is marked by a red eye and the straight, gray bill that gives the genus its name. This instrument tapers from a broad base to an unusually pointed tip. Short rictal bristles encircle its conical base. A median crest ranges between races from bright crimson to orange. It is raised only when the bird is excited.

Adult female plumage is more muted, and the crest is less conspicuous. In general, though, write Stiles and Whitney, "the sexes are too similar in appearance to be safely distinguished

in the field under any but the most favorable circumstances." Immature sharpbills resemble mature females, but with an even smaller scarlet crown.

Distribution

Sharpbills are scattered in discontinuous patches in Central America and South America. This curious dispersal may mark the remnants of a more widespread and continuous historical distribution.

In Central America, sharpbills inhabit northwest and central Costa Rica, including the Dota Mountains, and a majority of Panama. In South America, the species ranges from the Pantepui of southern Venezuela, Guyana, and Suriname, to northeastern and southeastern Brazil, including the Amazon. Sharpbills are also found in southern Paraguay and in central and eastern Peru.

Habitat

Sharpbills inhabit rain and cloud forests at 1,300–5,900 ft (400–1,800 m). In these humid montane regions, the birds can be found in dense primary forest, as well as along forest edges and in secondary growth. In some locations they have been observed descending to lowlands during nonbreeding seasons.

Behavior

The few accounts of sharpbills in the wild describe them as "stolid," even "sluggish" birds prone to brief bouts of abrupt movement. In between lengthy periods of branch sitting, sharpbills will launch into fast, direct flights between trees, or make rapid sorties for food.

They are most often solitary birds, and usually hang back even when part of mixed foraging flocks. Owing to their generally inconspicuous coloration and demeanor, sharpbills can be difficult to observe.

Stiles and Whitney observed male Costa Rican sharpbills (O. c. cristatus) alternate between vocalizing from conspicuous perches and active, but silent, defense of overlapping territories from other males. Noting that the defenders seemed happy to welcome females into those same territories, the authors concluded that the cluster of ranges functioned as an exploded lek (mating ground).

The sharpbill call is a high, rough, slightly descending trill, transcribed by one observer as "eeeeuuuurrrr." It has been likened to the call of cicadas, certain cotingas, and the three-toed sloth.

Feeding ecology and diet

Sharpbills mainly eat fruit and invertebrates. They either hop about the densely leafed canopy, or make short sallies among the outer twigs and leaves. In South America, sharp-bills have been observed feeding alone, in pairs, and in mixed flocks alongside tanagers, cotingas, woodpeckers, wood-creepers, and other small birds. Spiders, ants, berries, and seeds have been found in sharpbill stomachs.

To find its food, a sharpbill will often hang upside down from a branch, like a tit. It will also probe with its bill into tufts of moss, epiphytes, fruit pods, and tightly rolled leaves. Often the bird will then open its bill to reveal arillate seeds, or insect egg cases concealed inside the leaves.

This foraging behavior, known as "pry-and-gape," has been observed in other members of the Icteridae family. Still, it is considered a unique specialization among the Neotropical tyrannids, and it may provide an evolutionary explanation for the sharpbill's namesake appendage.

Reproductive biology

As late as the 1980s, the sharpbill was one of the last avian families whose mating and nesting habits remained a mystery. The first nest was not found until 1980, and courtship behavior has been rarely, if ever, observed. In their observations of the Costa Rican sharpbill, Stiles and Whitney concluded that some of the male activity, including perching hopefully next to females and following them into the foliage, qualified as courtship behavior.

The sharpbill breeding season probably occurs at the same time as its singing season. This extends from late February or early May, to late May, or early June.

The nest described by Brooke, Scott, and Teixeira was built by a female near the top of a 100-ft (30-m) tree in southeastern Brazil, 30 mi (50 km) from Rio de Janeiro. It consisted of a simple, shallow cup 3 in (7.8 cm) in diameter, slung underneath a slim horizontal branch. A thin outer surface of mosses, spider's webs, liverworts, and leaves may have been held together and suspended by dried saliva. Two eggs were incubated for 14–24 days, and the female fed the young by regurgitation. Observations suggested a nestling period of 25–30 days.

Conservation status

Since the species has yet to be studied in any depth, sharp-bills' conservation status and population size remain unknown. They have been described as uncommon or rare over much of their range. However, sharpbills are regularly seen in primary forests near Rio de Janeiro.

Significance to humans

Sharpbills have no known significance to humans.

Resources

Books

Perrins, C. M., ed. The Illustrated Encyclopedia of Birds. New York: Prentice Hall, 1990.

Sibley, C. G., and B. L. Monroe Jr. Distribution and Taxonomy of Birds of the World. New Haven: Yale University Press, 1990.

Wetmore, A. The Birds of the Republic of Panama. Vol. 3. Washington, DC: Smithsonian Institution, 2000.

Periodicals

Brooke, M., D. Scott, and D. Teixeira. "Some Observations Made at the First Recorded Nest of the Sharpbill Oxyruncus cristatus." Ibis 125, 2 (1983): 259–261.

Da Silva, J. M. C. "The Sharpbills in the Sierra dos Carajas, Para, Brazil, With Comments on Altitudinal Migration in the Amazon Region." Journal of Field Ornithology 64, 3(1993): 310–315.

Lanyon, S. M. "Molecular Perspective on Higher-Level Relationships in the Tyrannoidea Aves." Systematic Zoology 34, 4 (1985): 404–418.

Sibley, C. G. "The Relationships of the Sharpbill." Condor 86 (1984): 48–52.

Stiles, F. G., and B. Whitney. "Notes on the Behavior of the Costa Rican Sharpbill." Auk 100, 1 (1983): 117–125.

Julian Smith, MS