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First published online August 18, 2005
Journal of Experimental Biology 208, 3395-3407 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01769

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The kinematics of feeding and drinking in palaeognathous birds in relation to cranial morphology

Sander W. S. Gussekloo^* and Ron G. Bout

Institute of Biology Leiden, Evolutionary Morphology, Leiden University, Kaiserstraat 63, NL-2311 GP Leiden, The Netherlands

View larger version (15K): [in a new window]   Fig. 1. Types of cranial kinesis in birds. (A) Prokinesis, (B) distal rhynchokinesis, (C) central rhynchokinesis. Skull outlines are given in lateral view. Black triangles indicate the main area of rotation, multiple triangles in a single element indicate the boundaries of an bending zone. The triangle in A indicates the nasal–frontal articulation. Arrows indicate the lateral (nasal) bar of the upper bill, which is incomplete in C. Ligament is shown in gray. (Adapted from Zusi, 1984.)

View larger version (17K): [in a new window]   Fig. 2. Digitised points in each frame of the feeding scenes. (1) Rostral edge of the eye, (2) caudal edge of the eye, (3) centre of the ear, (4) centre of the food item, (5) upper bill, near the bill tip (ventral edge), (6) upper bill, rostral of the bending zone (ventral edge), (7) upper bill, caudal of the bending zone (ventral edge), (8) upper bill, caudal part (ventral edge), (9) upper bill, most rostral point with feathers, (10) lower bill, near the bill tip (dorsal edge), (11) lower bill, rostral of the bending zone (dorsal edge), (12) lower bill, caudal of the bending zone (dorsal edge), (13) lower bill, caudal part (dorsal edge), (14) throat, near end rhamphotheca, (15) throat, near end lower jaw, (16) throat, 2 cm below marker 15. In addition to the points shown, three standard points on the background grid were digitised to determine horizontal and vertical axes and to scale the images.

View larger version (14K): [in a new window]   Fig. 3. Outline drawings of feeding behaviour (A) and scoop drinking behaviour (B) of the greater rhea Rhea americana. Horizontal lines represent ground level in A or water level in B.

View larger version (34K): [in a new window]   Fig. 4. A characteristic feeding cycle of the greater rhea Rhea americana. The vertical broken lines indicate characteristic moments in the feeding cycle. In chronological order: (A) picking up the food item (grasp), (B) maximum gape during a repositioning cycle and (C) maximum gape during the transport phase. The graphs show the gape, the vertical (Y) and horizontal (X) positions of the head, the distance between the food item and the bill tips, the depression of the throat and the flexion of the most rostral part of the neck.

View larger version (25K): [in a new window]   Fig. 5. Oropharynx of the greater rhea Rhea americana. (A) Dorsal view of oropharynx floor. (B) Ventral view of oropharynx roof. a, rhamphotheca; b, tongue cushion; c, tongue base; d, opening of the trachea; e, larynx; f, esophagus; g, rhamphotheca; h, bony palate; i, soft palate; k, choana; m, vomer.

View larger version (31K): [in a new window]   Fig. 6. Measurements selected to describe the feeding behaviour of the greater rhea Rhea americana and used in the principal component analysis. Numbers in the graphs refer to parameters listed in Table 3. Measurements from the groups `gape', `lower bill', `prokinesis' and `rhynchokinesis' are correlated to the maximum gape during food pecking (gape 1; no. 1) and the maximum gape in the transport phase (gape 2; no. 2). Graphs of prokinesis, rhynchokinesis and lower bill depression are not given but they strongly resemble the pattern shown in the gape graph.

View larger version (15K): [in a new window]   Fig. 7. Plot of PC1 against PC2 of the analysis, including drinking behaviour. Different food types are represented by different markers, and groups of a single food type are outlined. Circles, large apple; closed squares, small apple; open squares, pellets; triangles, seeds; open circles, drinking behaviour.

View larger version (17K): [in a new window]   Fig. 8. Plot of PC1 against PC2 of the analysis of food types only. Different food types are represented by different markers, and groups of a single food type are outlined. Circles, large apple; closed squares, small apple; open squares, pellets; triangles, seeds.

View larger version (13K): [in a new window]   Fig. 9. Kinesis in the upper bill of the greater rhea Rhea americana. Squares indicate mean values (N=13, except at 0.24 s, where N=12) for each parameter at a certain time for the peck up phase with a medium sized food type (3: pellets). Vertical lines indicate 95% confidence intervals. The gape (A) is represented as the distance between the bill tips. Prokinesis (B), rhynchokinesis (C) and lower bill depression (D) are represented by change in angles (no absolute values). Negative angles for prokinesis and rhynchokinesis indicate elevation of the upper bill. Lower bill depression is represented by positive values.

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