The marble-burying test was performed according to previously described methods with minor modifications . Briefly, the apparatus consisted of a plastic box (15 × 10 × 10 cm) and 9 clean glass marbles (10 mm diameter) that were evenly spaced (4 cm apart) on sawdust (2 cm deep). The number of marbles that were at least 2/3 buried after 5 min was recorded.