The white-tipped sicklebill (Eutoxeres aquila) is a member of the diverse hummingbird clade Trochilidae, the most speciose group of non-passerine birds with over 300 species in over 100 genera (Sibley and Ahlquist, 1990). Hummingbirds are unique among birds in their small size (2 to 20 grams), elevated mean body temperature (~40° C), and rapid heart rate (up to 1,260 beats per minute) (Johnsgard, 1983). In fact, hummingbirds have the largest heart relative to body size of all endothermic vertebrates.

Hummingbirds have large sterna to support robust wing muscles, which contribute nearly 30% of an individual’s body weight. They fly by rotating the entire wing with little or no wrist and elbow flexing. Hummingbirds are capable of both forward and backward flight, and they even can sustain a hover. They can beat their wings up to 200 times per second, and the upstroke of a hummingbird produces as much power as the downstroke (Johnsgard, 1983).

Both traditional classifications based on morphology and more recent molecular data group hummingbirds and swifts (Apodiformes) together in the clade Apodimorphae (Sibley and Ahlquist, 1990). Trochilidae can be further broken into two smaller clades, Phaethornithinae (hermits) and Trochilinae (non-hemits); Eutoxeres is a member of the former. Monophyly of Phaethornithinae and Trochilinae are supported by both morphological (Hinkelmann and Schuchmann, 1997) and molecular data (Bleiweiss et al., 1994, 1887, 2004). These data also recover Eutoxeres as the sister taxon to all other Phaethornithinae.

Although living hummingbirds are restricted to the Western Hemisphere (they occur from Tierra del Fuego to Alaska; Sibley and Ahlquist, 1990), recent fossil evidence suggests that the group may have originated in the Old World. Recent paleontological research has recovered several European and Asian fossil taxa that lie just outside the crown clade Trochilidae (Mayr, 2003a,b, 2004, 2005). Eutotrochilus inexpectatus, collected from Oligocene deposits in Germany, is the sister taxon to the crown (Mayr, 2004).

Eutoxeres aquila ranges from Costa Rica to northern Peru. It is easily distinguished from all other hummingbirds by its extremely curved bill, which it uses to exploit the curved corollas of wild plantains and heliconia flowers. The bill is wide at the base, narrowing quickly near the terminus. In life, the maxilla is black and the mandible is yellow. Although E. aquila and its sister species, E. condamini, are not as brightly colored and iridescent as many hummingbirds, they do possess green and purple feathers on their wings, dorsum, and tails. In addition, their tails are tipped with white (Elliot, 1878; Hilty and Brown, 1986; Fjeldså and Krabbe, 1990).

Females lay two elliptical eggs in cup-like nests attached to the underside of leaves. The nests are typically small, with a diameter of around 50 mm, and one nest was reported to have been attached to a leaf by nothing more than cobwebs (Vigle, 1982).

Additional Information on the Skull

Click on the thumbnails below for labeled images of the skull in standard anatomical views.

Dorsal view	Lateral view	Ventral view

This specimen, a male, was collected 1 mile north of San José de Lourdes, Cordillera del Condor, Depto. Cajamarca, Peru by N. K. Johnson on 10 July 1983. It was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Timothy Rowe of The University of Texas at Austin. Funding for scanning and image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Rowe.

Lateral view of skull	Dorsal view of skull	Ventral view of skull

The specimen was scanned by Richard Ketcham on 21 December 2005 along the coronal axis for a total of 758 slices. Each slice is 0.053 mm thick, with an interslice spacing of 0.053 mm and a field of reconstruction of 20 mm.

Literature

Bleiweiss, R., S. L. Hendrickson, M. E. Berres, Y. O. Willis, and E. O. Willis. 2003. Affinities of the saw-billed hermit (Ramphodon naevius) determined by cytochrome-b sequence data. Wilson Bulletin 115:1-10.

Bleiweiss, R., J. A. W. Kirsch, and J. C. Matheus. 1994. DNA-DNA hybridization evidence for subfamily structure among hummingbirds. The Auk 111:8-19.

Bleiweiss, R., Kirsch, J. A. W. and J. C. Matheus. 1997. DNA hybridization evidence for the principal lineages of hummingbirds (Aves: Trochilidae). Molecular Biology and Evolution 14:325-343.

Fjeldså, J. and N. Krabbe. 1990. Birds of the high Andes. Zoological Museum, University of Copenhagen and Apollo books, Svendborg, Denmark, 876 pp.

Elliot, D. G. 1878. A classification and synopsis of the Trochilidae. Smithsonian Contribution to knowledge 317:1-277.

Hilty, S. L. and W. L. Brown. 1986. A guide to the birds of Colombia. Princeton University Press, Princeton, NJ, 836 pp.

Hinkelmann, C. and K. –L. Schuchmann. 1997. Phylogeny of the hermit hummingbirds (Trochilidae: Phaethornithinae). Studies of Neotropical Faunas and Environment 32:142-163.

Johnsgard, P. A. 1983. The hummingbirds of North America. Smithsonian Institution Press, Washington, D.C., 303 pp.

Mayr, G. 2003a. Phylogeny of early Tertiary swifts and hummingbirds (Aves: Apodiformes). The Auk 120:145-151.

Mayr, G. 2003b. A new Eocene swift-like bird with a peculiar feathering. Ibis 145:382-391.

Mayr, G. 2004. Old World fossil record of modern-type hummingbirds. Science 304:861-864.

Mayr, G. 2005. Fossil hummingbirds in the Old World. Biologist 52:12-16.

Sibley, C. G. and J. E. Ahlquist. 1990. Phylogeny and classification of birds: a study in molecular evolution. Yale University Press, New Haven. 976 pp.

Vigle, G. O. 1982. A nest of Eutoxeres aquila heterura in western Ecuador. The Auk 99:172-173.

Front page image.