November 1, 1897.] 



KNOWLEDGE. 



267 



identified by reference, or it is entirely a new species. In 

 any case the object carries its own credentials : no collateral 

 evidence is necessary. With an egg, however, the case is 

 different. Suppose a collector finds a nest on the ground, 

 say, with four or five bluish white eggs. They can only 

 be harriers'. True ; but which of the three ? Size is the 

 only criterion, and then they may be large Montagu's or 

 small hen harriers'. In no case would a conscientious 

 collector feel justified in admitting the clutch to his 

 collection without a very conspicuous query on the label. 

 Had he secured the bird, no doubt would have remained 

 to mar his triumph. But it is not always in the power, 

 nor, let ns hope, in the heart, of a collector to procure 

 evidence by these drastic means. He can, neverthe- 

 less, generally obtain the testimony afibrded by a clear 

 and repeated view of the bird, the position and structure 

 of the nest, and the locality. All these data he should 

 most carefully note. United to the character of the eggs 

 themselves, they will furnish tolerably conclusive evidence. 

 It must be noted, however, that the identification of an 

 egg from seeing the bird rise apparently from off the nest 

 is not invariably certain. Prof. Xewton cites the instance 

 of a purple sandpiper and a dunlin which had nested within a 

 few yards of each other. The sandpiper rose, and the col- 

 lector found the dunlin's eggs, whereat he was much amazed ; 

 but he searched further, and found the nest of the sand- 

 piper hard by. A less experienced individual would have 

 been contentei with his first find, and set down the dunlin's 

 eggs as varieties of the purple sandpiper. It is also a fact 

 that many birds wiU lay in old nests of other species. 

 Eider ducks' eggs have been found in gulls' nests. The 

 smaller Faleoni'lce are not above occupying the nests of the 

 crow tribe. The sparrow will oust the martin from her 

 laborious edifice. Then we have the parasitic birds — 

 cuckoos, and the cowbird of America. As a rule, the 

 intruder's egg can be readily enough distinguished from 

 those of the lawful inmate, but — with some of the cuckoos 

 at any rate — it is a fact that their eggs have come to 

 resemble those of the foster parents in an astonishing 

 manner, possibly because the parasite will always quarter 

 its eggs upon individuals of its own foster species. Mr. 

 Howard Saunders told me that when nesting in Malaga, 

 he was surprised to find numerous nests of the Orphean 

 warbler with one, or even two, apparently double-yolked 

 eggs ; but noting the prevalence of cuckoos (C. lanorus) in 

 that neighbourhood, he soon satisfied himself that this 

 bird was responsible for the large eggs. They resembled 

 those of the Orphean warbler so closely that it was only by 

 microscopic examination of the texture of the shell that 

 Mr. Sorby, F.R.S., was enabled to corroborate Mr. 

 Saunders' supposition. Having thus exposed a few of the 

 snares that beset the collector in his efforts after identifi- 

 cation, it now remains to discuss the light thrown on 

 ornithology, and even the wider domain of natural selection 

 with its side issues, by a study of fully authenticated eggs. 

 Oology as a Guide in Classification. — Prof. Newton 

 avers that ornithologists achieved a signal triumph when 

 the study of eggs led them to appreciate the intimate 

 relation of the snipes and plovers (Limicolce) with the gulls 

 {(iavicB) before any taxonomer had arrived at that con- 

 clusion, which, now that other testimony has assured it, 

 appears obvious on a casual comparison of eggs and 

 nidification. The one marked distinction appears to lie in 

 the number of eggs laid, which, with the tiavia, rarely 

 exceeds three, while the Limicolm generally lay four. But 

 this numerical difference is by no means constant, and, 

 apart from it, the likeness between some of the terns' and 

 sandpipers', godwits', curlews', gulls', and skuas' eggs is 

 remarkable enough to make an amateur wonder that, on 



that evidence alone, there could have been any hesitation 

 in accrediting the orders with the closest affinity. But 

 when one remembers that the owls and woodpeckers, also 

 of diS'erent orders, resemble each other very closely in the 

 absence of nidification, and the number and appearance of 

 their eggs, one feels it well to pause before relying entirely 

 on that evidence. For all that, eggs have proved most 

 useful finger-posts. Witness the Icterine warbler, classed 

 by Linnoeus with the Motacillidie. Not until the unmis- 

 takable and intensely characteristic eggs of the bird were 

 found was it relegated to its proper genus. Perhaps in no 

 other family do the egg variations correspond so uniformly 

 with the generic divisions as in the Sylricula. 



It is remarkable, too, how sharply the Falconidw are 

 separated by the character of their eggs, both as an order 

 and in their genera. The peculiar rusty, dried- blood 

 colour of their markings rarely varies in hue, though it 

 does so in tone ; and although the spots or splashes may 

 be of the faintest, as in the griffon vulture, the white-tailed 

 eagle, and others, yet they are nearly always present. I 

 need not point out the sharp distinction between the deep- 

 red eggs of the falcons proper and the greenish white 

 products of the harriers, except to suggest that the 

 sparrowhawk, with its clouded eggs, occasionally suffused 

 all over, would seem to form a connecting link between 

 the two. Also it is pleasing to note how closely the 

 magnificent individuality of our own honey buzzard's 

 eggs is reproduced in those of his Transatlantic brethren, 

 the American Pernis. 



Again, all the owls, without exception, lay pure white 

 eggs, and build no manner of nest. In these particulars, 

 but in no others, they resemble the woodpeckers and 

 parrots, especially the latter. It is possible that a similarity 

 of eggs may point to some remote relationship, some 

 common ancestry ; and it is not improbable that birds 

 laying glossy, globular eggs may be descendants from a 

 common ancestral centre, partaking of the nature of owl, 

 parrot, woodpecker, and kingfisher. 



The eggs of Pallas's sand grouse are similar to those of 

 certain species of goatsucker. The bird itself is a most 

 distracting blend of grouse and pigeon, but its eggs are 

 quite distinct from those of the game birds, in that they 

 possess a second set of markings — hke those of the plovers 

 — which the eggs of true game birds (grouse, etc.) do not. 

 The plovers mostly lay four eggs, the sand grouse and 

 pigeons two. But of the plovers, several — the coursers and 

 pratincolss to wit — rarely lay more than two eggs, and the 

 dotterel always three ; whQe the sand grouse, frequently, 

 and the pigeon, exceptionally, lay three. The nightjars, 

 or goatsuckers proper, invariably lay two eggs on the 

 ground, with no pretence at a nest. The sand grouse does 

 the same. But the owlet nightjars lay white eggs in holes 

 of trees, and the Australian frogmouths (PoiUuyiila) form 

 a kind of pigeon-like nest, in which they deposit two white 

 eggs. Here we have a strong link 'twist goatsucker and 

 pigeon, while, in the respect of colouring, there is a 

 wonderful resemblance between the eggs of goatsucker and 

 sand grouse. Certain Indian nightjars lay eggs which 

 could be easily mistaken for those of sand grouse. Then 

 the eggs of aU three families are so similar to each other 

 in shape, so distinct from all besides. The sides are straight, 

 or nearly so, and the ends equally rounded. The pigeon's 

 eggs curve slightly more than those of the other two. 

 To form a deduction from these data as to the possible 

 relationship between birds so dissimilar in their structure, 

 appearance, and habits, is one of the many problema that 

 confront him who would classify birds by their eggs. 



I would add a few remarks on the decided way in 

 which a bird will vindicate its individuality by its nidifica- 



