Vol. XIII. 



1913 



j Hull, The Eggs of Gymnorhina, spp. i^ 



The Eggs of Gymnorhina, spp. 

 By a. F. Basset Hull, R.A.O.U., Sydney. 



The eggs of the Australian Magpie {Gymnorhina, spp.) exhibit a 

 greater variation in colour and markings than those of any 

 other bird. Although amongst the eggs of the Guillemots, 

 Terns, and Gulls great variation is found in ground colour and 

 markings, there is a general similarity in the type, the variation 

 consisting largely in degree of intensity of ground colour or 

 quantity and disposition of the markings. The eggs of the Magpie 

 differ in actual colour, class and disposition of the markings, 

 shape, and size. At the same time these differences are not local, 

 or the result of food or environment, nor are they, except as to size, 

 known to exist in the units of a clutch or the successive layings 

 of an individual bird. In the case of the sea-birds marked 

 differences often exist between the separate units of a clutch, or, 

 where the bird usually lays only one egg for a sitting {e.g., 

 Onychoprion fiiliginosa) ^ and that egg is taken, the next laid varies 

 markedly from the first. The Magpie, on the other hand, is 

 consistent in that the units of a clutch are all of the same colour 

 scheme, varying slightly only in the disposition of the markings 

 and dimensions of the eggs, and the successive layings are of the 

 same type. Further, the known extreme departures from the 

 normal in the case of the sea-birds, such as the blue or red 

 mutations of Lams novcB-hollandice, are very rare. 



Taking No. 5 on the accompanying plate as a typical Magpie's 

 egg, perhaps 50 per cent, are in this colour. The actual departures, 

 not mere divergences from the type, are in overwhelmingly greater 

 proportion than in the case of any other species. 



The plate, produced from the originals by the three-colour 

 process, illustrates a unit from each of nine separate clutches of 

 the Black-backed Magpie's eggs {Gymnorhina tibicen, Latham). 

 While a much greater number of specimens showing marked 

 variations from type could be illustrated, these nine very fairly 

 represent the chief variations ordinarily found. Similar variations 

 are common to the other species of the genus — G. leuconota (Gray), 

 G. organicwn (Gould), G. dorsalis (Campbell), and G. longirostris 

 (Milligan). 



Is the remarkable variation in these eggs evidence of the gradual 

 evolution of a fixed type ? 



I would invite observers to favour me, through this journal, 

 with any interesting particulars relative to the eggs of this genus 

 coming under their notice, and especially evidences of the 

 persistence of a type in the successive layings of the one pair of 

 birds. 



The eggs shown on the accompanying plate, presented to the 

 readers of The Emu by Mr. H. L. White, of Belltrees, form units of 

 the following clutches : — 



I, +4, laid in captivity at Manly, N.S.W. 

 2, +3, taken at Burrenbilla, Q. 



