BIRDS (AVES) AS PALEOENVIRONMENTAL INDICATORS IN THE PLIO-PLEISTOCENE CAVE DEPOSITS OF GAUTENG PROVINCE, SOUTH AFRICA

The Plio-Pleistocene cave deposits of Gladysvale Cave and the Sterkfontein area have produced a large number of hominid fossils, and as a result have been the focus of intense paleoenvironmental study. While various types of data, including the mammalian fauna, palynological analysis, and isotopes, have been used to reconstruct the paleoecologic and paleoenvironmental context of these deposits and their biotas, most of the non-mammalian fauna, in particular the birds, have been underutilized for this purpose. The lack of their study is despite the presence of abundant and diverse bird bone assemblages.

Birds exhibit a wide variety of distinctive ecologic and habitat specific morphologies, and many clades have narrow ecologic and habitat preferences and/or requirements. These traits make birds an indispensable tool for reconstructing environments elsewhere. Here, I use bird faunas to reconstruct the paleoenvironments in South Africa. Some of the more common birds in these localities include mousebirds, pipits/wagtails, buttonquail, francolins, starlings, kestrels, rails, and estrildid finches. The bird faunas differ among the various cave deposits, and also indicate a heterogeneous paleoenvironment. None of these birds are inhabitants of caves (except perhaps the kestrels), and therefore the faunas likely represent the surrounding environment, not just areas adjacent to the caves. Comparison of the fossils with the preferences and occurrences of extant species in the same genera indicate the past presence of open grassland, marshy wet areas, thornveld/scrub, and thick dense brush/undergrowth. Buttonquail prefer grassy areas that are neither too dense nor too sparse, but patchy. The pipits and wagtails (Motacillidae) prefer grass with flowing water or rocky areas. The rails and other aquatic birds indicate presence of open bodies of water with shallow water (less than 30 cm deep) areas and deeper water (one meter or more), ringed by denser vegetation or reeds. These interpretations are consistent with that derived from other paleoenvironmental proxies, especially micromammals, and provide additional details not obtainable from analysis of other organisms.