3i6 



KNOWLEDGE & SCIENTIFIC NEWS. 



[January, igc6. 



The Colora.tion of 

 MaLmmoLls OLiid Birds. 



By J. Lew] 



Uonhote, M.A., K.L.S., F.Z.S., 

 .M.B.O.U., etc. 



I Continued from page 294.) 

 Ixt us now stufly for a short time the migrant birds 

 that breed in Pohir regions. These may be divided 

 into two chisses : — 



(i.) Those from tlie temperate regions, which 

 gradually breed as far north as is consistent 

 with their wants. 

 (2.) Tho.se that winter in the tropics and breed in 

 the extreme north, but not in the inter- 

 vening region. 

 We need not notice the first class here, as they 

 belong properly to the north temperate region, from 

 whicli they are stragglers. 



The second class consists, for the most part, of 

 bright-coloured birds that assume their bright livery in 

 the tropics, and that wear in winter a duller dress, 

 assumed in northern regions*. The Lapland bunting 

 (Calcanm lappouicus) is a good example, for the cock 

 ha.s n bright black and red breeding plumage, much 

 brighter than that of its near ally, the snow bunting 

 (Ph'clroplicnax nivalis), which has a much more north- 

 erly \\ inter habitat. 



.Another good instance of a bright-coloured northern 

 breeding bird is the red-breasted swallow [Hirundo 

 erythogaster), which passes the summer in North-East 

 Siberia, and the winter in Burma, and countries to the 

 south. This bird does not, as far as I am aware, 

 moult in these northern regions, and, consequently, 

 as we should expect, retains its bright red colour, 

 which was ;issumed in the tropics (where the tempera- 

 ture and food are conducive to high vigour) throughout 

 the year. 



It would be impossible to enumerate all the birds 

 which may be considered in this class ; the Limicolse 

 offer many examples, and the knot (Tringa caiiuius) may 

 be taken as very typical. 



This bird assumes in early spring, when in the 

 tropics, a very deep chestnut plumage. It then 

 migrates to the extreme north to breed. After breed- 

 ing it moults and becomes a dull greyish white bird, so 

 that both its plumages are in keeping with the colour 

 characteristic of the regions in which they are assumed. 

 \ow it has long been a puzzle to me whyf the young 

 knot, bred and reared in the north, should yet be able 

 to assume a browner and pinker plumage than its 

 parents, although in Arctic regions. The explanation 

 may, however, possibly be due to the fact that when 

 the old birds moult they have had a long journey im- 

 mediately followed by the strain of the breeding season, 

 compressed into the short .Arctic summer, so that we 

 would expect their vigour in autumn to be very 

 low; whereas, on the other hand, the young bird has 

 only had to grow, which is probably n" far less strain 



* It has been pointed out to me that some birds migrate in 

 autumn before tliev moul'. which is sometimes undoubtediv the 

 case, although I believe that in the majority of instances this is due 

 to their being driven south by early storms before the moult has 

 been completed. In any case the moult would follow so soon after 

 migration that their svslem would not have had time to respond to 

 the more generous influences of a southern clime. 



t For further suggestion on this point see P.Z.S. 1901, p. 325. 



on its system than that undergone by the parents. The 

 result is that the young are enabled, although in Arctic 

 regions,* to assume, to a slight extent, a colour belong- 

 ing rather to the tropics. 



This case is, to my mind, of considerable importance 

 as showing that " colour " is dependent far more on 

 " vigour " than on the particular latitude in which it 

 is produced. 



Knots, when kept in captivity, rarely, if e\er, assume 

 the full deep chestnut which they do when wild, the 

 amount of change depending largely upon the 

 individual. For two winters I endeavoured, by keep- 

 ing these birds at a fairly high temperature, to induce 

 them to assume their full red colour, but it produced no 

 appreciable effect, showing, therefore, that heat has, in 

 this species at all events, but little power. 



The golden plover at first sight offers rather a puzzle, 

 for in this species the birds, which nest in the southern 

 limit of its range, are duller and in less perfect plumage 

 than those to the north, which is apparently exactly 

 the reverse of what ought to take place. It ihas, how- 

 ever, been proved for some species of birds, e.g., 

 Geothlypis, that those individuals of a species that 

 breed the furthest north, winter furthest south, and, 

 consequently, the full plumaged golden plovers that 

 breed in the far north may presumably have wintered 

 in the tropics, while those that breed with us have never 

 entered the torrid zone. 



Further evidence in support of this suggestion is 

 given by that nearly-allied species, the grey plover, 

 whose breeding range is entirely in the north, and that 

 only occurs in the temperature zone on migration, for in 

 this species all individuals assume their full summer 

 dress. 



To take a further example. The ducks may be 

 roughly divided into two groups : — 



(i.) Those in which the male assumes a dull 

 plumage after the breeding season. (Re- 

 stricted entirely to those species in which 

 the sexes are markedly distinct.) 

 (2.) Those in which the male and female are simi- 

 larly coloured. (Chiefly found in the 

 tropics.) 



Of this latter group, the long-tailed duck (Harelda 

 glacialis] is the only species which occurs in Arctic 

 regions. 



This bird, moreover, differs in its plumage from all 

 other members of the .Vnatidae by the fact that there is 

 a summer and w-inter plumage common to both sexes. 

 -According to our present theory, this is quite easy of 

 explanation. The light-coloured winter plumage is 

 assumed in Arctic regions after the breeding season ; 

 the winter is spent in temperate regions, and the sum- 

 mer plumage produced there (imder conditions which 

 must be very mild to an .Arctic species) is brown. 

 II. — The Tropical Regions. 



Leaving the Polar regions, where the contrasts of 

 the seasons are greatest, let us now turn to the tropics, 

 where the contrasts are least. 



In the first place, the conditions are such that life 

 can be carried on in a high state of " vigour " during 

 all seasons of the year, and abundance of food in the 

 shape of fruit and insects may be had in every month, 

 the only seasonal differences being those of wet and dry. 



.Although these naturally have a considerable effect in 



* Of course the tendency of the species to assume red must be 

 taken into account, as it causes the bird to be pink instead of brown 

 on the breast, though the brown colour appears on the back. As I 

 previously pointed out (loc. fit. ante), the red plumage is in this 

 case probably the older plumage. 



