FIG. 8 in Adaptation of seedsnipes (Aves, Charadriiformes, Thinocoridae) to browsing: a study of their feeding apparatus

FIG. 8. — Forces in action when a fixed plant item is taken off; A, a plant item is pulled along the axis of the bill; B, a plant item is torn off by moving the head downward towards the breast. Abbreviations:F (= F' at equilibrium), clamping forces respectively exerted by the mandible and the upper jaw; Fr, resistance force of the item, labelled Fra when this item is pulled along the axis of the bill and Frb when this item is torn off by moving the head downward towards the breast (Fra = Frb); Ff, friction force which depends on the clamping forces: Ff = 2 k F (k = coefficient of friction); the lever arms of Fra and Frb are respectively indicated l and h, with l> h; so Fra has a less favourable lever arm than Frb: the action of these forces depending on their respective momentum, we have Fra × h