Mat 25, 1883.] 



♦ KNOWLEDGE • 



30i 



. MAGAZINE . ^I^CE 



FLAfNlYl|QRD£D-£XACT 4BlSCRI B£D, 



LONDON: FRIDAY, MAY 25, 1883. 

 Contents op No. 82. 



PAGB 

 A Solurelisfs Tear. XIII. The 



Blaikop Sings. By Grant Allen 303 

 Lsvrs uf Bristatness. {llltutmUd) 



Bv K. A. Proctor 3M 



Our Bodies. XII. The Bodr's 



Income and Expenditure. 87 



l)r. Andrew ■Wilson, F.R.S.E , 



4c. 



The Libraries of Babjlo: 



and 



306 



The Chcmistnr of Cookery. IX. 



Bt W. Mattieu Williama i 



Baldness I 



?jlgi 

 Sun Views of the Earth. (//;«»- 



Iratrd.) Bv R. A. Proctor 310 



Reviews: Ge'oloey Afield— WTlere 

 10 find Ferns ^ Guid.nce f..r 

 Youth— Paradoxical Fhilosophv 3'1 

 The Face of the Skv. By F.R.A.S. 312 



Editorial Gossip ...'. 313 



Correspondence: To Destroy 

 Aphides — A Discount Dodge — 

 A Musical Question— The Di- 



Tided Skin, 4c 311 



Our Chess Column 317 



Our Mathematical Column 318 



A NATURALIST'S YEAR. 



By Graxt Allex. 



XIII.— THE BLACKCAP SIXGS. 



\ JIONG the greening red-currant trees in the garden a 

 ^1. noisy wee bird sits perched invisibly under the shade 

 «£ the lush young foliage, and sings away in changeful 

 notes, which make it at first very hard to distinguish for 

 what it really in the end turns out to be. When it began, 

 it whistled gaily like a blackbird, and I thought for a 

 moment it must be one of those light-heartod strawberry- 

 coving thieves come to look up the chance of a ripe berry 

 or two on the blossoming vines in the early bed. Then it 

 struck out a plaintive note or so, like the nightingale's ; 

 and after that it glided off incontinently into the liquid 

 treble of the thrush and the garden warbler. Presently, 

 hopping from one bough, which it had fully cleared of the 

 £at black and yellow banded caterpillars, to another one, 

 as yet unweeded of its insect foes, it showed enough of its 

 head and wings above the broad currant-leaves to disclose 

 the fact that it was really our English mockingbird, the 

 lively little garden-haunting blackcap. Plain and unnotice- 

 able as he is in plumage, there are so many odd small points 

 of form or habit about him which cast light upon the origin 

 and history of specific distinctions that I shall make no 

 apology for taking him as the te.xt of this morning's 

 , «volutionary discourse. I can watch him through the 

 window as I write, and so make sure that I am keeping 

 my description of his appearance and manners thoroughly 

 true to the facts of nature. 



Your blackcap is Viy family one of the thrush kind, and, 

 by further restriction, he belongs to that lesser group, 

 justly known as the warblers, distingui-'hed (so far as outer 

 appearance goes) from the true thrushes mainly by the fact 

 that the young birds are unspotted on the upper part of 

 the body. This seems, no doubt, at first sight, a very small 

 and unimportant difference ; but then we must remember 

 that among such a closely similar class as birds generally, 

 the specific, and even the generic and family differences are 

 usually but slight ; and, further, that resemblances between 

 tlie young are almost always of high genealogical value, 

 because they presumably represent a common ancestral 



form, from which the adult creatures proceed to vary in 

 different directions. Thus, we may fairly conclude that at 

 some early period the original thrush group split up into 

 two minor divisions, one with spotted backs, and the other 

 with unspotted ; while in the course of time each of these 

 minor divisions once more subdivided itself, under stress 

 of more special selection, into the thrushes, blackbirds, and 

 field-fares on the one liand, and the nightingales, blackcaps, 

 and whitethroats on the other. ]Mr. Seebohm, one of our 

 greatest authorities on such subjects, believes that these 

 two main groups ought even to be ranked as separate 

 families, and points out that the diversity indicated by the 

 difference in the plumage of the young liirds is correlated 

 with other diversities in the mode of moulting, and in the 

 peculiar shape of the bone known as the /nrsiix. It must 

 be borne in mind that variations in the plumage are com- 

 paratively important as indicating specific separateness in 

 birds, and that the only marked difference (for example) 

 between a thrush and a blackbird is that the one is spotted 

 and the other uniformly black. Under such circumstances, 

 the constant presence of spots upon the back of the young 

 blackbird, which die away with the mature plumage, must 

 be regarded as a good hint of the original derivation of the 

 race. 



Our friend the blackcap, again, differs from the re- 

 mainder of his own relations, the restricted warblers, in the 

 possession of that little dark crest on the top of his head, 

 from which he has acquired his popular English name. 

 The hen birds, however, have the crest brown, instead of 

 black — a sort of distinction which commonly occurs in 

 similar cases. Here, in all probability, we have a very 

 simple instance of those decorative adjuncts -whose origin 

 Mr. Darwin ascribed to the selective preferences of the 

 female birds. In the closely-allied garden warblers the 

 sexes are indistinguishable, but in the blackcap a dis- 

 tinction of some importance has been set up ; and it is 

 interesting to learn from Mr. Harting, a close observer, 

 that till.' male blackcaps always arrive in England some 

 days before the females. The natural consequence must 

 be that the first and strongest females, when they arrive, 

 will be able to take their choice of the heartiest and 

 raost-decorated mates, as well as the best singers. Now, 

 it so happens that among the garden warblers, too, the 

 cock birds are the first to come ; and an objector might 

 easily ask why they also are not similarly decorated. 

 That is just the sort of objection which it is always 

 easy to raise against evolutionary reasoning, and the 

 answer to which is very simple. E%-erything must 

 have a Vieginning. However much decorated any 

 class may now be, there must have been a time when 

 it first began to acquire its earliest ornaments. Thus the 

 garden warblers may, perhaps, even now be starting on the 

 road toward the acquisition of a distinctive male topknot. 

 But, on the other hand, selection of this sort must be con- 

 stantly subordinated to natural selection of the strongest or 

 the bestrprotected individuals. Thus, it may also happen 

 that among the very civilised garden warblers, any extra 

 decoration might be harmful rather than useful. In short, 

 it is always relatively easy to account for what is — easy to 

 show why Englishmen with firearms get the better of Red 

 Indians with bows and arrows ; it is not always so easy to 

 account for what is not — to explain why Red Indians did 

 not invent gunpowder before the English. I may add that 

 the little white-throats also come to our shores before the 

 ladies of their kind, and skulk about in the hedges till the 

 hens arrive ; but as soon as this happens, they take their 

 stand conspicuously on the topmost branches by the way- 

 side, and sing emulously against one another for the attrac- 

 tion of their listening mates. To my mind, these incipient 



