Characterising the exploitation of avian resources: An experimental combination of lithic use-wear, residue and taphonomic analyses
Introduction
Feathers form a highly complex integumentary appendage found in the avian class, and they are characterised by an organised branched structure that grows according to a unique mechanism (Chuong and Widelitz, 1998). Feathers have always been admired by various cultures around the world and incorporated into both composite tools and garments. In the Americas, for example, indigenous cultures from Alaska to Patagonia employed feathers displaying an astonishing variety of shapes, sizes and colours to create items of both social and ritual significance. Colour plays a particularly important role in the selection of plumage for ornamental purposes. Efforts intended to change or emphasise tonalities have been documented in some native populations (Azevedo Luíndia, 2004) and the predetermined combination of feathers with different colours during the manufacture of artefacts is sometimes connected with deep symbolism (Lívero Sampaio and Pobikrowska Tardivo, 2010). In ecosystems rich in avian species, feathers have repeatedly been used as ornaments in diadems, headdresses, wristbands, earrings, cloaks, capes and sceptres (Levine, 1991, Lívero Sampaio and Pobikrowska Tardivo, 2010). Further, in geographical areas where the same colourful specimens were not available, feathers appear as a constant within the material culture (Levine, 1991, Pearlstein et al., 2012). Feathers have also been technologically important, featuring in complex chaînes opératoires like the fletching of arrows (Bartram, 1997, González-Ruibal et al., 2001) and the making of artificial flies for fishing. Moreover, on the basis of rock art paintings, the worldwide use of plumage throughout prehistory has been extensively documented, from its utilisation in ornaments and rituals to its employment in the fletching activity (Obermaier and Wernert, 1919, Jordá Cerdá, 1971, Pessis, 2003, Borges do Lago, 2008, Martin, 2008, Viñas, 2014). Sometimes pigments with different and lighter tonalities from the substrate of the paintings were used to highlight ornamental feathers (Viñas and Morote, 2013).
Although the ethnographic literature has established that birds have been hunted for both their meat and plumage, the importance of avian resources during prehistory has only recently become a topic of investigation. The exploitation of bird carcasses is usually inferred from taphonomic studies (Fiore et al., 2004, Blasco and Fernández Peris, 2009, Blasco and Fernández Peris, 2012, Peresani et al., 2011, Finlayson et al., 2012, Morin and Laroulandie, 2012, Blasco et al., 2014, Romandini et al., 2014, Radovčić et al., 2015), whereas direct evidence of bird residues, such as feather fragments, is much more difficult to document because of preservation constraints. When they are documented, feathers usually appear as micro-fragment remains on the surfaces of stone tools (Robertson, 2002, Dove et al., 2005, Hardy and Moncel, 2011). Sometimes, the identification of birds from archaeological residues has been performed to the level of either species (Dove and Peurach, 2002, Dove et al., 2005) or order (Hardy et al., 2001, Hardy et al., 2013, Robertson, 2002).
Because this kind of evidence is rarely encountered, a refined methodology for its documentation and description has yet to be formulated. This is why we have focused on the creation of a suitable methodology for identifying the exploitation of avifaunal resources during prehistoric times. Based on the assumption that lithic tools were employed to butcher the animals and, subsequently, to work the plumage (if employing it for ornamental or technological purposes), we considered the two types of evidence most likely preserved in the archaeological record: use-wear and micro-residues of organic matter. Therefore, evidence related to experimental avian bones and experimental flint tools was documented in an attempt to understand whether or not cut marks on the bones were correlated with the identified use-wear on stone tools. The proposed methodology combines lithic and faunal examinations, with special attention to the microscopic characterisation of feather fragments adhered to the lithic surfaces. Especially regarding residue identification, a strong methodological foundation is needed for the analysis of the archaeological material. Researchers have yet to establish an experimental reference for comparison with the archaeological evidence. Before we attempt to identify ancient feather fragments on lithic tools, we need to clearly define their diagnostic attributes that are discernible under the microscope and to select the microscopic techniques that will provide the best results.
Feathers are highly ordered, branched structures that are intricately formed in order to endure the aerodynamic forces involved in flight. They also play a fundamental role in the thermo-regulation of birds. A combination of stiffness and lightness is necessary to confer the ability to fly, converging in a singular structure. Feathers are composed of two main portions, a central shaft and the vanes extending from it (inner and outer vanes) (Fig. 1). The shaft must be resistant to damage and consists of two segments, the calamus and the rachis. The calamus is a relatively short tubular structure with a slight elliptical cross-section, which is attached to the skin of the bird. The remainder of the shaft is termed the rachis and bears the vanes of the feathers.
There are different types of feathers. The major ones are contour feathers. They have the same basic structure exhibited by all feather types, with barbs branching out from the rachis, as well as barbules, which in turn branch from the barbs. The barbs resemble microscopic feathers in appearance, meaning that they are composed, as feathers are in general, of a central shaft named the ramus (or rachilla) to which the barbules (the smallest division of feathers) are attached (Fig. 1: 1–4). Two barb/barbule types are recognised: downy (or plumulaceous) ones located in the proximal portion of the vanes (at the proximal part of the feather) near the calamus, and pennaceous ones located in the central and distal portions of the vanes. Barbules consist of a base and a pennulum (Fig. 7: F). The base is located near the ramus, whereas the pennulum displays different microscopic features depending on the barbule type. Pennaceous barbules are interlocked by tiny structures called hooklets, whereas downy ones bear diagnostic features used for the identification of bird orders and even species. In fact, the morphology and distribution of the nodes, which are the junctions of the cells composing plumulaceous (downy) pennulum barbules, vary depending on bird species (Dove, 2000, Dove and Koch, 2010).
The main constituent of the compact parts (rachis and rami) of avian feathers is keratin, a polypeptide common in the structural components of the body tissues of other vertebrates, such as mammalian fur, hoofs, horns, beaks and claws. Keratin (from the Greek keras, meaning horn) refers to a family of fibrous proteins composed mainly of 20 different amino acids (among them glycine, alanine and cysteine). Cysteine deserves special mention for being rich in sulphur and playing an important role in the stability and cohesion of keratins (McKittrick et al., 2012). There are two primary groups of keratins, α-keratins and β-keratins, which are distinguished from each other in terms of their structure, composition and properties. The α-keratins are present mainly in mammalian hair, horns and claws, whereas the tougher β-keratins are the main components of reptile scales, beaks and feathers (Huggins, 1980).
Section snippets
Experimental series
A series of pilot experiments involving two bird species, griffon vulture (Gyps fulvus) and short-toed snake eagle (Circaetus gallicus), was conducted. Two carcasses, one for each species, were butchered using five non-retouched flint flakes. All the flint flakes were obtained from a unique chert nodule probably originated in calcareous lithofacies/formation. The chert nodule was collected on the floodplains of the Francolí River (Tarragona, Spain).
The experiments were designed with the
Use-wear patterns
Use-wear was poorly developed on the experimental flakes we analysed, even if, as in some cases, they were used for a considerably long time. The butchering of large mammals does not usually result in major changes to the lithic micro-surfaces, although differences in wear development on experimental and ethnological artefacts have been described (Beyries, 1993). A lower degree of use-wear development should be expected subsequent to butchering small game animals, considering the shorter
Residues on archaeological record
Usually, when we analyse micro-residues, we are dealing with a set of methodological problems. First, many residues display overlapping morphologies. Particularly when we consider single fibres, we frequently find very similar morphologies and colourings, no matter which residue types we are looking at. Difficulties in discerning residue types as a result of using optical light microscopy (OLM) alone have been reported elsewhere (Lombard and Wadley, 2007, Monnier et al., 2012, Monnier et al.,
Conclusions
By combining data from different disciplines, we presented preliminary experimental data intended to suggest an innovative method for better determining the degree of exploitation of avifaunal resources by prehistoric human groups. A major effort was made to establish the base for a solid experimental method, in order to be further able to interpret the avifaunal impact in the diet of prehistoric human groups. After an initial phase comprising the performance of pilot experiments, we plan to
Acknowledgements
We thank all those involved in the experiments for helping us to perform the study reported here, especially Jordi Rosell, Maite Arilla, Jordi Fàbregas, Ignacio Martínez, Laura Llorente and Ignacio Aguilar for their comments and very useful assistance during the series. Special thanks go to Clive Finlayson and the Gibraltar Museum for providing us with the necessary materials for our study and allowing us to use some of their photographs (Fig. 2 B and C). The authors also thank Andreu Ollé for
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