ORNITHOLOGIST 



—AND- 



OOLOGIST. 



$1.00 per 

 Annum. 



PUBLISHED BY FRANK B. WEBSTER. 



Established, March, 1875. 



Single Copy 

 10 cents. 



Vol. XV. 



BOSTON, MASS., JANUARY, 1890. 



No. 



Geographical Variation of Eggs. 



Altlioufrli tlie subject of fteogvapliical vari- 

 ation of birds has at various times received 

 considerable attention, I am not aware tliat 

 miicli t!i<iu<;bt lias been bestowed on the pres- 

 ence of a similar difference in e<iss, and tliink- 

 in<; that the little information I have been 

 able to f^ain upon this question mi<rht be of 

 some value to the readers of the Ohnitiioi.o- 

 (iisT AND Ooi.ooisT, I have made the following 

 summary of my researches in that line, hopinji' 

 that it will at least draw the attention of those 

 better able to investi<;ate the matter than my- 

 self, to <;ive their ideas and the results of their 

 investigations for the jterusnl of those 

 interested. 



Ain<ni»>" the birds themselves local variation 

 has been systematized to a ccmsiderable degiee 

 by the works of Baiid and of Allen, and ac- 

 cording to their observations may be divided 

 into two classes, viz. : variati<ni in color and in 

 size. 



Eggs unquestionably vary in color in a luii- 

 forni degice, but the great lange of individual 

 coloration makes it impossible to establish 

 the general laws without a far greater amount 

 of comparable material than 1 have been able 

 to obtain, but vaiiation included under the 

 second heading, is to a certain extent as appli- 

 cable to eggs as to the birds themselves. 



The researches of Prof. Baird on the sul>ject 

 of geographical variation have established the 

 l:nv that "a gradual decrease in size, in indiv- 

 iduals of the same species, occurs in direct 

 ratio to the decrease of latitude or altitude of 

 their birthplace," and this seems with a greater 

 number of exceptions to hold good in the case 

 of eggs. 



As there are more conditions which intlnence 

 the size and structure of an egg to a greatei- 

 degree than among birds, a larger per centage 

 of them would naturally be expected to be in- 

 consistent with anv general rule or law. 



Some of the influencing conditions would be 

 age of one or both parents, varying number 

 laid in a set, number of consecutive clutches, 

 and the scarcity and variety of food. Exam- 

 ples of the first of these influences will be ap- 

 parent to all who are in any way familiar with 

 birds. A good one which I call to mind is the 

 eggs of Fish Hawks (Pandiou halUeetua car- 

 oUrifnxix), for as these birds return yearly to 

 the same nest, the chances for observation are 

 greatly increased. Among them the oldest 

 birds usually lay eggs which average smaller 

 than those of younger pairs, or else the number 

 in the set is smaller. 



Traces of the second infiuencing condition 

 are n()t always perceptilde, especially among 

 eggs which are only found in small sets, but 

 even then are occasionally noticeable. 



Among the Gnllina' and Plr!(l(e, both fami- 

 lies being prolific layers, the effects of the 

 third condition are freiiuently noticeable, and 

 one instance will l>e sulficient tor illustration, 

 that of a Flicker {Colaptes aurntus). that laid a 

 set of ten eggs, which upon being removed laid 

 a second set of five. The average measure- 

 ment of the first set was 1.11 x .84 of an inch, 

 while the maximum of the second set was .!»!» 

 X.92, and the minimum .9(5 x .SO. 



Besides the foregoing there are occasicmally 

 instances where the great variation amounts to 

 a monstrosity, and seems to be inconsistent 

 with any law, but as these monstrosities are 

 freipiently or always infertile, they do not bear, 

 with any importance, upon the question in 

 consideration. 



So much for statements. Now for the cor- 

 roborating data. The following list of meas- 

 urements will show the variation of eggs from 

 different parts of the country. The measure- 

 ments represent the size in inches and hun- 

 dredths, but vary fr(»m ordinary measurements 

 insomuch as the averages of the two diameters 

 are given, or in other words give the size of a 

 spherical bulk of the same capacity as the egg 

 it represents. 



Copyright, 1800. by Fkank B. AVkbstkk. 



