ICHNOLOGY OF HOLOCENE AVIAN TRACKS, CAICOS AND SAN SALVADOR ISLAND, BAHAMAS ARCHIPELAGO

Many shorebirds spend time moving over unconsolidated carbonate sediments along the coasts of islands in the Bahamas Archipelago. Innumerable tracks and trackways with the potential for preservation in the rock record are created during the lifetime activities of each bird. The Bahamian ichnofossil record comprises a rich diversity of invertebrate and plant traces, yet few fossil tracks attributed to an avian trace-maker have been reported.

Studies of modern avian species and their track-generating behaviors provide information that can aid in the discovery and elucidation of ancient trackways. Two examples are described of Holocene tracks preserved during the early lithification of carbonate sands.

A single tridactyl track occurs in beachrock at Turtle Cove, Caicos. The track lacks a hallux or metatarsal pad and is asymmetric with robust digits. Track length (T_L) is 43 mm and track width (T_W) is 34 mm. This track size overlaps those of three shorebird species that are known to reside on Caicos: Willet, Greater Yellowlegs and American Oystercatcher. In modern tracks, Greater Yellowlegs register slim toes while those of Willets and American Oystercatchers are more robust. Oystercatcher tracks are more asymmetric than those of Willets and Greater Yellowlegs, with toe 2 being shorter than toe 4. These observations suggest that an American Oystercatcher may have been the trace-maker of the Caicos track.

A trackway comprising two complete and three partial tracks occurs in lithified sediments at the backshore/dune interface at French Bay, San Salvador. The tracks are tridactyl, nearly symmetrical and lack hallux or metatarsal pad. Maximum divarication angle of 120˚, T_L 18-30 mm, T_W 29-30 mm and stride 126-143 mm indicate that a medium-sized shorebird made these tracks. Comparison with the characteristics of tracks of shorebirds that commonly occur in The Bahamas suggests either a plover or a sandpiper as the most likely trace-maker.