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

Abstract

Cranial kinesis is an important feature in avian feeding behaviour and involves the transmission of quadrate movement to the upper bill by the Pterygoid-Palatinum Complex (PPC). The PPC in Palaeognathae is remarkably different from that found in Neognathae. In this study we analyse whether the special morphology of the PPC is an adaptation to the feeding behaviour of the Palaeognathae. Behavioural analyses of the rhea Rhea americana showed that the feeding behaviour of the rhea is typical 'Catch and Throw' behaviour, independent of the size of the food item. Drinking is achieved by a scooping movement followed by a low-amplitude tip-up phase. During feeding rhynchokinetic movements of the upper bill were observed. However, cranial kinesis was limited and may differ from rhynchokinesis in neognathes as a clear bending zone seemed absent. Since the movement patterns are considered very similar to the basic feeding behaviour in neognathous birds it is concluded that the specific morphology of the PPC is not the result of specific functional demands from palaeognathous feeding behaviour.

Gross anatomical features of the tongue, lingual skeleton and laryngeal mound of Rhea americana (Palaeognathae, Aves): morpho-functional considerations

“…Although the laryngeal mound of ratite species is reported to be smooth (McLelland 1989) and is a feature noted in D. novaehollandiae (Crole and Soley 2010a), many bird species display pharyngeal papillae on the laryngeal mound caudal to the glottis (King and McLelland 1984;Bailey et al 1997;McLelland 1989). The considerable variation in the appearance and number of pharyngeal papillae noted in the present study was a feature not previously reported for R. americana (Faraggiana 1933;Bonga Tomlinson 2000;Gussekloo and Bout 2005). This variability in size, number and appearance suggests that the pharyngeal papillae may be rudimentary in nature and are not an integral part of the functioning of the laryngeal mound.…”

“…A renewed interest has recently been shown in the morphology of the upper digestive tract of commercially important ratite species, particularly Struthio camelus (Linnaeus, 1758) (Tivane et al 2006;Porchescu 2007;Jackowiak and Ludwig 2008;Tadjalli et al 2008, Tivane 2008Guimarães et al 2009) and Dromaius novaehollandiae (Latham, 1790) (Crole and Soley 2009a, b, 2010a, b, 2011, as well as in the feeding mechanism employed by this group of birds (Bonga Tomlinson 2000;Gussekloo and Bout 2005).…”

“…These studies vary from gross morphological descriptions of the tongue of Rhea pennata (Orbigny, 1834) (Cho et al 1984), Casuarius casuarius (Linnaeus, 1758) (Gadow 1879;Pycraft 1900), S. camelus and D. novaehollandiae (Faraggiana 1933;Cho et al 1984;Bonga Tomlinson 2000) to macroscopic and microscopic studies of the tongue of S. camelus (Porchescu 2007;Jackowiak and Ludwig 2008;Tivane 2008;Guimarães et al 2009) and detailed studies (including light and scanning electron microscopy) of the tongue of D. novaehollandiae Soley 2009a, b, 2010b). In contrast, only minimal information on the morphology and function of the tongue (Owen 1835;Faraggiana 1933;Feder 1972;Bonga Tomlinson 2000;Gussekloo and Bout 2005;Santos et al 2011) and laryngeal mound (Owen 1835;Faraggiana 1933;Bonga Tomlinson 2000;Gussekloo and Bout 2005) of Rhea americana (Linnaeus, 1758) has been published. The most extensive study of the lingual skeleton is that of Bonga Tomlinson (2000) although its presence was also mentioned by Feder (1972).…”

“…The feeding method of R. americana has been documented, and the role of the tongue and hyobranchial apparatus during feeding has been described (Bonga Tomlinson 2000; Gussekloo and Bout 2005). However, the morphological peculiarities of the tongue and lingual skeleton of R. americana may reflect additional functions and therefore a more advanced specialisation of these structures, as opposed to representing a basic ancestral form (Bonga Tomlinson 2000) due to their apparent simplicity in comparison with other ratite species.…”

Contrasting morphological evidence for the presence of taste buds in Dromaius novaehollandiae and Struthio camelus (Palaeognathae, Aves)

“…However, it is more probable that the pores represent the openings of underlying glands, as no histological evidence of taste buds was supplied. Ratite species swallow their food whole, employing the 'catch and throw' (Gussekloo and Bout 2005) or cranioinertial feeding method (Bonga Tomlinson 2000), in which the food lands near or within the oesophageal entrance prior to swallowing. As a result of this method of food intake, there would be a limited need or opportunity for taste during the intra-oral transport of food.…”