342 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
wing measurements, etc., and, except for the number of specimens 
obtained and their sexes, no further detail. A rough guess can be 
made at the date of collection from the time of year during which 
the collection was made, but this even is often impossible. There is 
rarely any indication as to whether the species was common or 
whether the specimens collected were the only ones observed, whether 
the bird was resident, on passage, or in winter quarters. Again, how 
frequently the major value of a paper is lost by failure to grasp the 
importance of assigning subspecific value to those specimens which 
represent geographical races. The occurrence of the song thrush in 
Portugal is of little value without knowledge as to whether the bird 
is of the British or continental race; or, again, the passage of the 
redstart in Egypt or Palestine loses its importance without a deter- 
mination of its subspecific rank, which alone helps us in studying 
the bird's distribution and migration. 
It is perhaps ungenerous thus to criticize the great efforts made by 
field and museum naturalists, but the writer himself being an 
offender in this respect, reference is made to this most important 
point in the hopes of stimulating further effort to gain the maximum 
results from the slaughter of such beautiful creatures as birds, to 
enable us to interpret correctly the many and varied facts with which 
nature presents us and to solve the complex problems of distribution 
and migration, ^o killing -of birds can be justified merely to com- 
pile a list of species obtained in a certain locality. Careful field 
notes by the collector and an accurate determination of subspecific 
rank (where this exists) by the man who works out the collection 
can alone justify its formation. A mere list of birds likely to be 
found in almost any part of the world could be compiled by any 
studious ornithologist in the library of the Zoological Society in 
Regents Park, without a visit to the locality in question and with- 
out taking the life of a single bird. 
Neither are we dealing with a science which is stationary. Geo- 
grajphical distribution and migration have been in the past, are now, 
and always will be fluctuating, sometimes imperceptibly, sometimes 
by leaps and bounds. The same applies to the geographical races of 
a species. As distribution and migration alter, so do subspecies 
become evolved, usually very gradually, but sometimes within the 
lifetime of man. But the problems remain constant, and the laws 
which govern these problems change but little. 
The extent of the geographical distribution or range of a species, 
on which largely hinges the differentiation in both species and sub- 
species, is due to — 
1. Gradual expansion or contraction. 
2. Periodic and regular migration. 
