To examine the hydrodynamic propulsion mechanism of a diving great crested grebe (Podiceps cristatus), the three-dimensional kinematics was determined by digital analysis of sequential video images of dorsal and lateral views. During the acceleration phase of this foot-propelled bird, the feet move through an arc in a plane nearly normal to the bird's line of motion through the water, i.e. the toes move dorsally and medially but not caudally relative to the water. The kinematics of the grebe's lobed feet is different from that in anseriforms, whose feet move in a plane mostly parallel to the bird's line of progress through the water. Our results suggest that the foot-propelled locomotor mechanism of grebes is based primarily on a lift-producing leg and foot stroke, in contrast to the drag-based locomotion assumed previously. We suggest that the lift-based paddling of grebes considerably increases both maximum swimming speed and energetic efficiency over drag-based propulsion. Furthermore, the results implicate a new interpretation of the functional morphology of these birds, with the toes serving as a self-stabilizing multi-slotted hydrofoil during the power phase.

REFERENCES

Carbone
C.
,
De Leeuw
J. J.
,
Houston
A. I.
(
1996
).
Adjustments in thediving time budgets of tufted duck and pochard: is there evidence for a mix of metabolic pathways?.
Anim. Behav
51
,
1257
–.
Cooper
A.
,
Penny
D.
(
1997
).
Mass survival of birds across the Cretaceous—Tertiary boundary: Molecular evidence.
Science
275
,
1109
–.
Cracraft
J.
(
1982
).
Phylogenetic relationships and monophyly of loons, grebes and Hesperornithiform birds, with comments on the early history of birds.
Syst. Zool
31
,
35
–.
Dickinson
M. H.
(
1996
).
Unsteady mechanics of force generation in aquatic and aerial locomotion.
Am. Zool
36
,
537
–.
Fish
F. E.
(
1996
).
Transitions from drag-based to lift-based propulsion in mammalian swimming.
Am. Zool
36
,
628
–.
Johansson
L. C.
,
Lindhe Norberg
U. M.
(
2000
).
Asymmetric toes aid underwater swimming.
Nature
407
,
582
–.
Lovvorn
J. R.
,
Jones
D. R.
(
1991
).
Effects of body size, body fat and change in pressure with depth on buoyancy and costs of diving in ducks (Aythya spp.).
Can. J. Zool
69
,
2879
–.
Lovvorn
J. R.
,
Jones
D. R.
,
Blake
R. W.
(
1991
).
Mechanics of underwater locomotion in diving ducks: drag, buoyancy and acceleration in a size gradient of species.
J. Exp. Biol
159
,
89
–.
Norberg
R. Å
(
1973
).
Autorotation, self-stability and structure of single-winged fruits and seeds (samaras) with comparative remarks on animal flight.
Biol. Rev
48
,
561
–.
Rosser
B. W. C.
,
Secoy
D. M.
,
Riegert
P. W.
(
1982
).
The leg muscles of the American coot (Fulica americana Gmelin).
Can. J. Zool
60
,
1236
–.
Stephenson
R.
(
1994
).
Diving energetics in lesser scaup (Aythya affinis, Eyton).
J. Exp. Biol
190
,
155
–.
Stephenson
R.
,
Lovvorn
J. R.
,
Heieis
M. R. A.
,
Jones
D. R.
,
Blake
R. W.
(
1989
).
A hydromechanical estimate of the power requirements of diving and surface swimming in lesser scaup (Aythya affinis).
J. Exp. Biol
147
,
507
–.
Stolpe
M.
(
1935
).
Colymbus, Hesperornis, Podiceps: ein Vergleich ihrer hinteren Extremität.
J. Orn
83
,
115
–.
Tucker
V. A.
(
1993
).
Gliding birds: reduction of induced drag by wing tip slots between the primary feathers.
J. Exp. Biol
180
,
285
–.
Webb
P. W.
(
1988
).
Simple physical principles and vertebrate aquatic locomotion.
Am. Zool
28
,
709
–.
Woakes
A. J.
,
Butler
P. J.
(
1983
).
Swimming and diving in tufted ducks, Aythya fuligula, with particular reference to heart rate and gas exchange.
J. Exp. Biol
107
,
311
–.
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