SCIENCE-GOSSIP. 



17 



ON COLOURING OF BIRDS' EGOS. 

 By Reginald J. Hughes. 



MR. WHELDON in his last article (Science- 

 Gossip, vol. vi., N.S., p. 362) shows very , 

 clearly the difficulties and anomalies which arise 

 in attempting to account for the markings on 

 birds' eggs, either by the nature of their food or 

 the theory of protection, and I agree to a con- 

 siderable extent with many of his remarks. 



With permission, I will attempt to review the 

 present state of our knowledge of this subject as im- 

 partially as possible. I consider Mr. Wheldon has 

 proved that the nature of the food can have no effect 

 in the case of, at any rate, those pigments whose 

 principal basis is carbon, and which do not contain 

 iron. Carbon is an important constituent of all 

 organic substances, and it can form colouring 

 matters of many tints, so that animals with similar 

 diets could produce differently coloured pigments, 

 and vice versa. Thus we have on many eggs, besides 

 the blue oocyan, brown, red, and yellow pigments — 

 named by Mr. Sorby " rufous ooxanthine, lichen 

 ooxanthine, and yellow ooxanthine " — which are 

 carbonaceous and contain no iron. Again, the 

 dark skin of negroes is caused by melanin, a com- 

 pound of carbon, oxygen, hydrogen, and nitrogen, 

 and hence cannot be affected by their diet, since 

 all food-substances contain these elements. The 

 case of iron seems to me somewhat different. It 

 will hardly be disputed that some foods contain 

 a larger proportion of iron than others. A 

 herbivorous animal must consume less of it 

 than a carnivorous one, and a granivorous 

 bird gets even less from the seeds it eats than 

 it would from a diet of, for instance, grass. 

 Yet, as Mr. Wheldon points out, the amount in 

 the haemoglobin of all warm-blooded animals 

 is approximately the same. It is evident that the 

 surplus iron is got rid of in some manner, and the 

 simplest explanation of iron-containing pigments 

 on feathers or eggs seems to be that some is carried 

 by the blood as impurities into the radii of each 

 feather while young, and into the glands that 

 secrete the shell-staining matter. I do not think 

 . that every radius has a special gland to extract 

 the pigment ; the deposit is chiefly mechanical, 

 aided probably by the action of light. Glands, 

 however, no doubt, do take an important part in 

 the formation of the colour destined for the eggs, 

 and modify it to a great extent. There are many 

 instances of the deposit in extremities of the body 

 of impurities in the blood. A botanical analogy 

 is the secretion of superabundant silica in the 

 edges of blades of grass, and the readiness of blood 

 to perform this function is shown by the liability 

 of poisons to affect the tint of the feathers. It 

 should be noticed that carbonate of iron does not 

 act like poisons, as, instead of discolouring, as in 

 the case of hemp-seed, it intensifies the natural 

 colours. It is known that the blood of birds con- 



tains more iron at one time than at others, especially 

 before the egg-laying period, as is well shown by 

 the reddening of fowls' combs. The primary 

 reason is, no doubt, that an extra quantity is 

 required to furnish the contents of the eggs, the 

 yolk especially containing much iron. In spring 

 birds obtain a more abundant supply of food 

 furnishing this element. The surplus appears in 

 the male in the brighter colours of his spring dress : 

 in the hen it is used among granivorous birds 

 entirely for the contents of the eggs ; but I believe, 

 in the case of insectivorous species and others 1 hat 

 obtain a large supply of iron, some of that still 

 remaining unused is deposited on the shell. 



It seems to me that any argument on the relation 

 of diet to the colour of eggs must apply equally 

 well to that of the feathers ; so, although the pig- 

 ment, of birds marked -principally by melanin and 

 other carbonaceous substances may not be the 

 same as that on their eggs, and neither may bear 

 any relation to the food — yet the majority with 

 feathers containing zoonerythrin, the pigment, 

 which most probably contains iron, should, if my 

 theory is correct, have eggs coloured chiefly by 

 oorhodine and should feed on matter containing 

 comparatively much iron. That this is the case 

 we have at present insufficient evidence, and some 

 apparent exceptions, though there are certainly a 

 great many instances of it, and I hope to return to 

 this subject at some future time. Possibly there is 

 no general rule for explaining the colours of birds' 

 eggs, and the best way to do so will turn out to be 

 by examining the case of each species in detail, 

 and considering all the causes — such as habits, sur- 

 roundings, heredity, and food — which may have 

 influenced the result. 



Norman Court, Southsea. 



HONOURS FOR MEN OF SCIENCE. 



Among the honours commemorating her Majesty 

 Queen Victoria's birthday in 1900 several men of 

 learning and science are included. Professor Richard 

 Calverhouse Jebb, Litt.D., D.C.L., LL.D., Regius Pro- 

 fessor of Greek, and Conservative Member of Parlia- 

 ment for Cambridge University since 1891, has re- 

 ceived a knighthood. Sir Richard Jebb was born 

 in 1841 at Dundee. Dr. David Gill, C.B., J.P., LL.D.. 

 F.R.S., H.M. Astronomer Royal at the Cape of Good 

 Hope since 1879, becomes a K.C.B. Sir David Gill was 

 born in 1843 in Aberdeenshire. Prof essor Thomas 

 Edward Thorpe, Ph.D.,D.Sc, LL.D., F.R.S., Director 

 of Government Laboratories, London, is created a 

 C B. He is President of the Chemical Society. 

 Dr. Thorpe was educated at Owens College, Man- 

 chester and the Universities of Heidelberg and 

 Bonn. Dr. Thorpe was born near Manchester in 

 1815. Major-General Thomas Fraser, C.B., C.M.G.. 

 Commandant of the School of Military Engineering 

 at Chatham since 1896, and General Officer com- 

 manding Thames District, is promoted to K.C.B. 

 He was born at Chilham Castle. Kent, in 1840. 



