From Robert Shaw 16 December 1876
Glassaugh, Portsoy, | Banffshire. N.B.
16 December 76.
Dear Sir
You are hardly logical in rejecting a possible solution of a seemingly mysterious fact without being able to suggest anything more feasible.1 I am very well persuaded that if we could stop up the orifices in the humeri of a Condor or kite, he would ⟨c⟩ease from that moment ⟨t⟩o be a continuously soaring ⟨b⟩ird. All flying birds can ⟨so⟩ar for a little way by the momentum of exerted ⟨f⟩light, which will sustain ⟨the⟩m by forcing them over the underlying air by means of a series of ascending planes—the longer primaries—thus2
Mr. Buckland believes the soaring eagle to be “an animated balloon” by means of rarified air in the hollow bones.3 You think this inadequate but it can surely be partly operative. Now in add⟨ition⟩ to the heated air in the bones, it is a scientifica⟨lly⟩ necessary physiologi⟨cal⟩ fact which cannot be re⟨a⟩sonably contradicted, tha⟨t⟩ every quill throughout t⟨he⟩ whole plumage, from ⟨the⟩ largest to the smallest, must be filled with air rarified by the heat of the body. Take a large live bird in your hands and feel how warm he is. Birds are therefore enclosed from beak to tail in a rarified-air vesture. To enable this you will find in every feather an almost infinitessimal communication with the outer air, at the junction ⟨of⟩ the quill with the pith. ⟨I⟩ have often, (being an old ⟨s⟩portsman) shot land birds which fell on the water, where for a time, ⟨I⟩ never cared to try how ⟨l⟩ong) they floated like a cork, which, having regard to the specific gravity of their bodies, I must assume to have been by means of the warmly-aerated clothing. But I have still stronger inferential proof that Mr. Buckland and I are right. The Albatross, nearly allied to the gulls, is a soaring bird as I can testify.4 To my knowledge also it has hollow bo⟨nes⟩ with an orifice near t⟨he⟩ head of the humerus. ⟨The⟩ common gulls of our coa⟨st⟩ though of ⟨ex⟩ceedingly strong flight d⟨o⟩ not soar, and they hav⟨e⟩ solid bones—i.e. in com⟨mon⟩ parlance, for they are slightly cellular like bones in general.
I believe the gannet is a soaring bird.5 If so I feel assured he has the hollow bones of the albatross and falconidæ6 with the perforated humerus, and that this is a law running through this whole division of the animal kingdom. I have written to Edinburgh to enquire, and shall probably let you know the result, but I can ⟨a⟩lmost predicate it. ⟨T⟩here can be no such ⟨e⟩ffect as we observe in these gracefully soaring birds without an active efficient cause, for they cannot come under any exceptional laws of dynamics, and if the cause I have suggested be rejected recusants are bound in reason to show some other as probable, but I take it they can show no other whatever, and must rest in the bewildered wonderment of King Solomon.7
I have shown what I believe to be a marve⟨l⟩lously beautifull pro⟨vi⟩sion of Nature and ⟨I⟩ should be rather gla⟨d⟩ to see it accepted by men of science, to the glory of God.
I do not know whether the Grouse–Partridge question will have any interest for you. My predecessor in the tenancy of Glassaugh shot two and quite agrees with my view, but there are others who do not. I ⟨a⟩m credibly informed ⟨by⟩ men who have seen the hybrids that the Capercailyce and the phea⟨s⟩ant also have been known to cross with the “grey hen” i.e. the mate of the “blackcock” or “black grouse”.8
Pray excuse this lengthy intrusion on your time.
Yours faithfully | Robert Shaw | Major General
P.S. Unless King Solomon went into the “hill Country” he never saw an Eagle in flight, but he could n⟨ot⟩ look from his palac⟨e⟩ window without seeing scores of Kites I shall be glad if you will keep & reconsider my printed letter.9
Please cite as “DCP-LETT-10723,” in Ɛpsilon: The Charles Darwin Collection accessed on