174 



KNOWLEDGE. 



[ArousT, 1901. 



western Europe, no colour-chauge takes place in the 

 mountain hares of Ireland, while it is reported that in 

 those introduced into Ayrshu'e and the neighbouring 

 counties of south-western Scotland the change is much 

 less complete and regular than in those inhabiting the 

 northern parts of the country. 



An impression appeai-s to be prevalent that in the 

 more northern portion of their range both the mountain 

 hare and the ermine (or stoat) are white at all seasons, 

 but this does not seem to be authenticated. 



Obsei-v'ations are wanting as to whether the changes 

 of coat and colour in the mountain hare bear any 

 relation to the appearance and disappearance of snow, 

 or whether they occur regularly at the same season of 

 the year. In the case of the ermine in the Adii'ondack 

 region of Xew York. Dr. C. H. Mennam tells us that 

 in this animal the white livery is assumed only after 

 the first fall of snow, while the resumption of the brown 

 does not take place till the snow begins to melt. 

 Unfortunately, he says nothing in regard to change of 

 coat. The late Dr. Coues stated, however, that in the 

 case of the ermine the bi-annual change of coat takes 

 place at the same season, but that it depends upon the 

 condition of the temperature at the time whether the 

 new coat differs in colour from its predecessor. In other 

 words, the change from brown to white might be due 

 either to shedding the coat or to bleaching of the hair 

 subsequent to such shedding. The case of the mountain 

 hare is, however, stronglv suggestive that the colour- 

 change is in all instances coincident with the shedding 

 of the coat. 



It is, of course, quite evident that the assumption of 

 a white winter livery by mountain hares and ermines 

 living in regions where the snow lies on the ground for 

 a considerable portion of the year is for the pui-pose of 

 rendering such animals as inconspicuous as possible 

 when in their native haunts. And, so far as we know, 

 such a change is universal among the species named 

 when dwelling in high northern latitudes. 



There is, however, another animal inhabiting the 

 north polar regions of both hemispheres in which the 

 change to a pure white winter dress is limited to certa.in 

 individuals. The species in question is the Aixtic fox, 

 of which the beautiful fur, in both the white and the 

 blue phase, is now much affected by ladies. That both 

 the white and the blue individuals of this species are 

 in the winter dress, will be evident to every one who 

 examines such furs carefully; the length and thickness 

 of the hail- being quite decisive on "this point. 



As it has been stated in several works that the white 

 IS the winter and the blue the summer phase of the 

 Ai-ctic fox, it may be well to quote from a letter written 

 to me in answer to enquiries on this subject by Dr. Einar 

 Lonnberg. of Upsala, whose observations are based on 

 jjersonal experience : — 



" The ' blue ' foxes," he writes, " are uniformly dark- 

 coloured summer and winter, and do not change to white 

 at any time. In the summer they are very dark — dark 

 brown in fact; in winter they are also da'rk, but more 

 bluish. The individuals which turn white in winter are 

 during the summer ashy giey on the upper-parts and 

 limbs, but have the tail, under-parts, more or less of the 

 flanks, and the eais and muzzle white. The distribution 

 of the gi-ey and white is, however, subject to individual 

 variation. The 'blue' fox is, in fact, merely an 

 individual variety of the white one. Both breed 

 together, and sometimes there are dark and light 

 individuals in the same litter. A friend of mine 



observed on Bear Island a pair in which the female was 

 white and the male blue. In Iceland it is stated that 

 all the Arctic foxes are blue. 



With this single exception it appears that the white 

 and the blue phase are met with throughout the habitat 

 of the species. In other words, the animal is 

 ■■ dimorphic," if it be permissible to apply this term 

 to a case where the difference between the two phases 

 of a species is restricted to coloration. 



"What makes the matter so puzzling is that if " blue " 



I foxes are able to thrive during winter in a snow-clad 



country, what necessity is there for their fellows — and, 



indeed, for any species — to turn white at that season 



of the year? 



THE WHITE NILE-FROM KHARTOUM TO 

 KAWA. 



AN ORNITHOLOGISTS EXPERIENCES IN THE SOUDAN 

 By Harry F. Witherby, f.z.s., si.B.o.r. 



j III— THE COUNTRY AND THE PEOPLE. 



My last article^ treated of the river and the stretches 

 of grass and mud bordering upon it. Fringing the mud 

 j and stretching inland, for half a mile or so in most 

 i parts, but in some places for two miles, is a belt of wooded 

 I country. The trees composing this belt are chiefly of 

 the acacia familj-, many of them being of a gum-bearing 

 species, and under and around them is a thick under- 

 growth of mimosae, cacti, and other bushes. At the 

 time of our visit the trees and shrubs, with few 

 exceptions, were practically bare of leaves, so that, had 

 it not been for the thickness of the trees there would 

 have been but little cover. 



Vegetation seemed entirely at a standstill, and the 

 hot season might well be termed the winter in this 

 district, especially as the general breeding season for the 

 birds was over. Of the 141 species of birds which we 

 identified only four or five appeared to be nesting. A 

 small lark, which lived on the ground and continually 

 sought the shade of some bush, made the neatest little 

 nest in the diy mud by the river. The nest was a small 

 shallow ■■ cup ' composed of dry grass and a few bits 

 of cotton, while round the cup was a compact and neatly- 

 arranged layer of particles of mud. Only one egg was 

 laid. Two species of doves were also nesting. The nest 

 and eggs of onej of them were much like those of our 

 Turtle Dove. The other,§ which was a pretty little long- 

 tailed bird, built an exceedingly slender nest even for 

 a dove. It was round in shape and only 3i inches in 

 diameter. The two eggs were of a dark creamy colour. 

 The young were most quaint objects lightly covered 

 with whitish down. The smallest-{i of the many shrikes 

 which we found was the only one breeding. I watched 

 a pair at work on their neat chafiinch-like nest, which 

 was placed in a fork of a horizontal bough some 30 feet 

 uji an acacia. The birds brought material at intervals 

 of a minute or less during the considerable time I 

 watched them. They invariably sat in the nest and 

 turned rapidly round in it as they built in each mouthful 

 of stuff which they brought. The outside of the nest 

 they plastered with cobwebs. 



As the diy season affects the foliage of the trees, so 

 does the river influence their grovsi:h. When the river 

 is at its greatest height many of the trees on its flat 



* Knowledge, June, 1901. 

 § Oena capen-fU (Linn.) 



+ Turlur ambiguus, Boc, 

 II Nilatis affr (Lath,) 



