284 
FOREST AND STREAM 
June, 1919 
THE VARIATIONS IN BIRDS’ EGGS 
INDIVIDUAL DIFFERENCES IN BIRDS’ EGGS AS TO FORM. COLOR AND NUMBER IN 
CLUTCH ARE BUT PHASES IN THE EXPRESSION OF UNIVERSAL. BIOLOGICAL LAWS 
By ROBERT CUSHMAN MURPHY 
A t this season our native birds, in 
response to the instinct of repro- 
duction are preparing to build 
their nests and. after a period of incu- 
bation, to produce the first brood of 
spring. Already several species of owls, 
and some of the hawks, have finished 
their parental duties, and are now bring- 
ing food to half -grown fledglings; and 
even the bluebirds and song sparrows 
and other small birds are carrying nest- 
ing materials to the chosen sites in an- 
ticipation of the coming set of eges. 
“Birds-egging,” as our British friends 
call the custom of gathering the ex- 
quisite shells that have thrilled so many 
ardent young naturalists in years gone 
by, is a hobby which boys are no longer 
encouraged to ride. For generations be- 
fore the present, however, how many 
youngsters have risen at peep o’dawn of 
a spring day to raid some tempting nest 
ere the sun should bring forth the con- 
serving power of public sentiment! Who 
has not duplicated the direful experience 
of Tom Brown (or was it one of his 
equally incorrigible cronies?) who 
smashed the addled kestrel egg in his 
mouth when he adopted this delicate 
means of bringing it safely from the nest 
to the ground? And who of us, alas, has 
not seen his cabinet of blown shells, which 
had been assembled with such zeal and 
tenderness, consigned gradually to dust, 
bugs, mice, and oblivion, unless perchance 
a small brother or a local museum gave 
him the opportunity of unloading a half- 
troubled conscience and the remains of 
a collection — of which the recipient ac- 
cepted only the latter? 
For those who have carried their love 
of birds’ eggs into manhood, and who, 
after carefully choosing their field, have 
made the collecting of nests and eggs 
only one phase of their study of life his- 
tory and other branches of ornithology, 
there is of course, a happier prospect. 
Much scientific work of a high order has 
been accomplished by naturalists of this 
type. Major Bendire’s “Life Histories of 
North American Birds” being an excel- 
lent example of a standard book prepared 
by a man who was an oblogist or student 
of eggs. The most useful of egg collec- 
tions have been, as a rule, those of pri- 
vate enthusiasts, for the field of biological 
science is so large, and the distractions 
of the staff of a natural history museum 
so many, that the greater number of 
birds’ eggs in public museums are kept in 
safe but more or less unprofitable stor- 
age. Duplicating, to a large extent, simi- 
lar material elsewhere, the average mu- 
HE Natural History Depart- 
ment has been for nearly half 
a century a clearing-house for in- 
formation of interest to all. Our 
readers are invited to send any 
questions that come under the head 
of this department to Robert Cush- 
man Murphy, in care of Forest 
AND Stream. Mr. Murphy, who is 
Curator of the Department of Na- 
tural Science in the Brooklyn 
Museum, will answer through these 
columns. — [Editors.] 
seum collection of eggs unfortunately ac- 
complishes no dynamic purpose in the 
advance of science. 
There has recently been founded at 
Santa Barbara, California, the “Museum 
of Comparative Oology,” an institution 
dedicated solely to the preservation and 
study of birds’ eggs and nests. This 
seems an eminently proper step. Freed 
from the rivalry of other branches of 
zoology, the officers of such a museum 
may hope eventually to accumulate the 
first truly representative collection of 
eggs from all parts of the world. I 
should like to see the major part of all 
the really valuable egg material in the 
country go to such a centralized, special 
museum, instead of being scattered as it 
is now. The museum might then become 
a clearing house of whatever scientific in- 
formation may be derived from the study 
of eggs and nests, and a laboratory where 
students of oology might engage in seri- 
ous research. It would do much toward 
discouraging general and haphazard col- 
lecting, and would educate naturalists to 
see the greater desirability of collecting 
toward the perfection of this special mu- 
seum. 
P ROBABLY everyone who has looked 
at birds’ eggs, whether in the nests, 
or in the cases of museums, has 
noted their great variation. Some are 
plain-colored, others daubed and splashed 
with many pigments; some are laid in 
sets of two or three, while other sets may 
contain half a score; but how many per- 
sons have even guessed that the vast 
range in the number, form, and color of 
eggs is governed by definite laws, and 
that each character is the product of 
definite circumstances? Yet this is the 
truth of the matter, and during the last 
half century many of the laws governing 
these characters have been discovered. 
The significance of the number of eggs 
in a clutch is perhaps the most obscure 
of the three kinds of variations. The 
number ranges from one to as many as 
twenty, and with some exceptions birds 
of closely related species lay approxi- 
mately the same number of eggs. Con- 
sidering all birds as a group, and ignor- 
ing a few specific aberrations, the rule 
may be deduced that the ratio of the 
number of eggs varies in direct propor- 
tion to the likelihood of their destruction 
by natural agencies. Thus most ter- 
restrial nesters, such as the grouse and 
Water fowl, lay a large number of eggs, 
and it is evident that both eggs and 
young of these birds are much more lia- 
ble to destruction by natural enemies 
than the eggs or young of tree-dwelling 
species. But, on the other hand, the 
members of the large order of shore 
birds, for example the snipes and plover, 
lay sets of not more than four or five 
eggs although they, too, nest upon the 
ground. It is not improbable, however, 
that owing to their environment, young 
shore birds are less often molested by 
hawks and small carnivorous mammals 
than the grouse, and moreover, they sel- 
dom fall a prey to predacious fish and 
turtles which accounts for the loss of so 
many wild ducks in the early post-natal 
stages. The fecundity of a bird is not 
indicated by the number of eggs in a 
clutch, for the ovaries contain a large 
number of partly formed eggs which or- 
dinarily become developed only when 
the first set is destroyed. A few para- 
sitic species, such as the cowbird, oc- 
casionally deposit in the nests of other 
birds as many as forty or fifty eggs in 
a season, but since the cowbird is poly- 
androus, such unusual production may 
be caused by the extraordinary stimula- 
tion of the ovaries. 
F orm in eggs includes two attributes 
— shape and size. The significance 
of shape is twofold; in the lower 
forms it possibly denotes to a certain 
extent the status of the bird in the ani- 
mal kingdom, that is, its relative proxim- 
ity to reptilian forms from which all 
birds have presumably evolved. The 
grebes, which are rather low in the class, 
lay peculiar eggs in that both ends are 
nearly alike, presenting a biconical ap- 
pearance not unlike the eggs of certain 
reptiles. But the relation of the shape 
of the egg to the character of the nest 
has a far more obvious meaning, and is 
indeed one of Nature’s most beautiful 
examples of special adaptation for pro- 
tective purposes. The most familiar 
