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Show SEXUAL SELECTION : BIRDS. PAitT IL 8~ · f th condi.t i.o ns of l'1~1 0. But with many direct actwn o 0 ] bt that the summer l)ircls thoro can h'a rdly be a <.on 1'1 1 b th sexes arc a I w. . tal even w 1en o · plumage JS ornn.men ' ' . is tho case with many \Vo may ronclurle that t1ns . . their beautiful ~ f , they ncqnne herons, egrets, ~: rc., or b 1' cr season 1\'Ioreovcr, 1 1 : cr tho reecmb-, · Plumes on y C lUll\-, l cr}l l)OSSessed by bot1 l such rlumes, t op-1-~1 l u. ts' ' &. c ., t lOU.o l . o·hly develope d l.1 l · . 11 r a httle more llb sexr s, arc occaswn<t ) ' . 1 they resemble t 11 e h · the female , anc tho male t an m 1 b the males a1 o ne l . outs 1)o:sessoc Y b plumes a.nc omam. l·nown that confinement, y of other birds. It IR also ~ t of male birds, fre-affecting the repro<.l uc tive sv" s emt of th' eir secondary quenUv chec1 .: s tl developmen 10 h 'mmediate influence on sexual • char,a ct er.s , but as ln o I 1 ' 1\f . am informed by l ' r. any other characters ; a~c . us of the Knot . l t or mne speCime Bn,rtlett that e~g 1 . l tl ir unadorned winter plu- . t s) retamec 1e l . (T?·tnr;~ canu ,u l o·icn.l Gardens throughout t lO year, mn.ge m the Zoo ob . f tl at t1le summer plumage . .r t may m or 1 from w hwh J.ac wet both sexes r ar·tal·es of the nature ~ ' though comm.on 0 r plum::we of many other of the oxduslvcly mascu me b l)irds. 75 • f. cts more especially from From the foregor?g . al ' l no·I'ncr colour during f ·t n bm s c 1a b o neither sex o cer ai 1 . g so slightly that the l lt or c 1angm . either mmua mon ' . · to them and from h ·dl be of any servwe ' . change can a1 Y . lting twice yet retam- 1 f ther specws mou the fema es o o l t the "'ear we may con- 1 · throng wu J ' ' ing the samo co our.s f ltino· twice in the year ha elude that the hablt o mou b , t. on moulting, sec, on snipes, -,.-, I n r<:>gmc· l to the. .p rcviou::; :;tntemcu :; . 371 . on Glnrco1ro, l3 ··t Birds, vo1. lV. p. , . • (i30 xc l\Iacgillivray, 'Illst. n . ' ·rei's of India,' vo1. tit. p. G~5,_ . , ~n;·lcwi:!, nntl bustnr~ls.' J ordon, 0 .n~n tllo plumes of ll?rm~s, Ilm1, ~· r ·:~. on 'l'ot:.ums, lbld, p .. 70 ,4"" nm14H an<l 1\ir. Staflord A1lo ' ;38' n,nd 1\'Inegillivray, vo1. lV. p. ..,;J ' {n ~lw 'Ibis,' vol. v. 1SG:3, p. R3. 'C IIAP. XIH. DOUBLE ANNUAL J\IOULT. 83 not been acquired in order that the male should assume during the breeding-season an ornamental character; but that the double moult, having been originally acquired for some distinct purpose, has subsequently been taken advantage of in certain cases for gaining a nuptial plumage. It appears at first sight a surprising circum. tance .that with closely-allied birds, some species should regularly undergo a double annual moult, and others only a single one. The ptarmigan, for instance, moults twice or even thrice in the year, and the black-cock only once: some of the splendidly-coloured honey-suckers (Neetariniro) of Indiaand some sub-genera ofoLscurelycoloured pipits (Anthu ) have a double, whilst others have only a single annual moult. 76 But the gradations in the mannet· of moulting, which are known to occur with vari<ms birds, shew us how species, or whole groups of species~ might have originally acquired their double annual moult, or having once gained the habit, have again lost it. With certain bustards and plovers the vernn.l moult is far from complete, s0me feathers being renewed, and some changed in colour. There is also reason to believe that with certain bustards and rail-like birds, which properly undergo a double moult, ~=:orne of the older males retain their nuptial plumage throughout the year. A few highly modified feathers may alone be added during tho spring to the plumage, as occurs with the disc-formed tail-feathers of certain drongos (Blwinga) in India, and with the elongated feathers on the back, neck, and crest of certain herons. By such steps as these, the vernal moult might Le rcn-iii On tho moulting of the pta11nigan, sec Gould's 'llir<ls of Groat .13rit.aiu.' On the honey-suckers, Jordon, 'Birds of Indin,' vo1. i. p. 359, :10.3, 3GD. On tho moulting of Anthus, see Blyth, in 'Ibi.,,' 1867, p. 32. G ~ |