[72] “On the Flight of Birds, of Bats, and of Insects, in reference to the subject of Aërial Locomotion,” by M. de Lucy, Paris.
[73] M. de Lucy, op. cit.
[74] The grebes among birds, and the beetles among insects, furnish examples where small wings, made to vibrate at high speeds, are capable of elevating great weights.
[75] “The wing is short, broad, convex, and rounded in grouse, partridges, and other rasores; long, broad, straight, and pointed in most pigeons. In the peregrine falcon it is acuminate, the second quill being longest, and the first little shorter; and in the swallows this is still more the case, the first quill being the longest, the rest rapidly diminishing in length.”—Macgillivray, Hist. Brit. Birds, vol. i. p. 82. “The hawks have been classed as noble or ignoble, according to the length and sharpness of their wings; and the falcons, or long-winged hawks, are distinguished from the short-winged ones by the second feather of the wing being either the longest or equal in length to the third, and by the nature of the stoop made in pursuit of their prey.”—Falconry in the British Isles, by F. H. Salvin and W. Brodrick. Lond. 1855, p. 28.
[76] The degree of valvular action varies according to circumstances.
[77] Of this circle, the thorax may be regarded as forming the centre, the abdomen, which is always heavier than the head, tilting the body slightly in an upward direction. This tilting of the trunk favours flight by causing the body to act after the manner of a kite.
[78] I have frequently timed the beats of the wings of the Common Heron (Ardea cinerea) in a heronry at Warren Point. In March 1869 I was placed under unusually favourable circumstances for obtaining trustworthy results. I timed one bird high up over a lake in the vicinity of the heronry for fifty seconds, and found that in that period it made fifty down and fifty up strokes; i.e. one down and one up stroke per second. I timed another one in the heronry itself. It was snowing at the time (March 1869), but the birds, notwithstanding the inclemency of the weather and the early time of the year, were actively engaged in hatching, and required to be driven from their nests on the top of the larch trees by knocking against the trunks thereof with large sticks. One unusually anxious mother refused to leave the immediate neighbourhood of the tree containing her tender charge, and circled round and round it right overhead. I timed this bird for ten seconds, and found that she made ten down and ten up strokes; i.e. one down and one up stroke per second precisely as before. I have therefore no hesitation in affirming that the heron, in ordinary flight, makes exactly sixty down and sixty up strokes per minute. The heron, however, like all other birds when pursued or agitated, has the power of greatly augmenting the number of beats made by its wings.
[79] The above observation was made at Carlow on the Barrow in October 1867, and the account of it is taken from my note-book.
[80] It happens occasionally in insects that the posterior margin of the wing is on a higher level than the anterior one towards the termination of the up stroke. In such cases the posterior margin is suddenly rotated in a downward and forward direction at the beginning of the down stroke—the downward and forward rotation securing additional elevating power for the wing. The posterior margin of the wing in bats and birds, unless they are flying downwards, never rises above the anterior one, either during the up or down stroke.
[81] That the elytra take part in flight is proved by this, that when they are removed, flight is in many cases destroyed.