Avian fauna, palaeoenvironments and palaeoecology in the late quaternary of the Western and Southern Cape, South Africa

Avery, Graham

Avian fauna, palaeoenvironments and palaeoecology in the late quaternary of the Western and Southern Cape, South Africa

Doctoral Thesis

1990

Publisher

University of Cape Town

Department

Department of Archaeology

Faculty

Faculty of Science

Abstract

Avian remains in coastal archaeological samples from Eland's Bay Cave, Die Kelders Cave 1 and Nelson Bay Cave in the Cape Province, South Africa, cover the periods between 80 000 and 40 000 B.P. and 18 000 and 300 B.P. Results of modern comparative surveys indicate that beached birds provide a predictable food supply. Kolmogorov-Smirnov two-sample nonparametric tests confirmed the close resemblance between the relative proportions of seabirds in archaeological and beached assemblages and earlier assumptions that the composition of seabird samples in archaeological sites could not otherwise have been achieved. It is shown that this simple but effective practice has a history going well into the Middle Stone Age. Kolmogorov-Smirnov tests for differences between the relative proportions of skeletal elements of Cape cormorants preserved in archaeological and modern jackal accumulations provided a useful means of drawing attention to possible activity of jackals and/or domesticated dogs. Recognition that diagenesis in some earlier samples may mimic the characteristics of modern jackal samples has established the need to extend the comparison of skeletal elements to additional species and to study the relative durability of avian skeletal elements. Similar comparison with the proportions of modern mammalian and avian predator prey species and size (mass) categories provided no indication that black or martial eagles might have contributed to the samples. Similarly, present knowledge of Cape eagle owls argues against their being likely inhabitants of caves suitable for occupation by people. It is concluded that people were the primary accumulators of the assemblages studied and that the role of small food items in prehistoric subsistence can be addressed with greater confidence. Correspondence analysis was used to determine the existence of seasonality in the modern beached seabird samples. The profiles of the archaeological samples are plotted in relation to months in which they were most likely to have been collected. Seasonal evidence from species not subjected to the correspondence analysis supported these results. The results obtained closely supported the hypothesis for seasonal exploitation of the coast. It was also possible to indicate that visits were probably of short duration and that their timing varied. Exploitation of seabirds did not coincide with the period of maximum availability of beached birds. Comparison of the avian evidence with that from seals, Cape dune mole rats and steenbok/grysbok suggested that small food items comprised part of a seasonal strategy that made maximum use of a range of seasonal resources. Evidence for significant local environmental change in addition to, and in support of, existing information has been obtained. Fluctuations in marine, freshwater and terrestrial birds at Eland's Bay Cave have been related to evidence for changes in terminal Pleistocene and Holocene sea levels and the position of the coast, and in the morphology of Verlorenvlei. At Die Kelders Cave 1 between 80 000 and 40 000 B.P., previously drier conditions were ameliorating and mixed scrub and grass and freshwater existed on the coastal foreland in the vicinity of the cave. Fluctuations in frequencies of seabirds indicate that the sea level rose slightly and then receded during the period of deposition. At Nelson Bay Cave samples indicate the approach of the coast after the Last Glacial Maximum, the disappearance of grassland and its replacement by scrub and bush as significant elements of the vegetation. Freshwater birds did not respond as expected, however, indicating that their interpretation at Nelson Bay Cave is complex and not consistent with evidence for wetter or drier conditions. A possible link has been shown to exist between fluctuations of albatrosses, petrels and shearwaters at Nelson Bay Cave and the intensity of wind patterns which are related to oceanic and atmospheric circulation. Further investigation should establish whether seabirds would provide an index of climatic conditions without support from other sources.