the north and who are temporarily driven abroad in the fall by 
stress of temperature and lack of food, only to return home again 
as soon as physical conditions allow. The summer excursionists 
go into a foreign land far away from their ancestral home or point 
of origin as a species, to perform the highest act of their lives, that 
is, the production of offspring. The winter-w'anderers breed, as 
good conservatives should do, upon their ancestral acres but are 
obliged to be wanderers therefrom during many months of the 
year. 
The Marek In the Omithologisches Jahrbuch for 1906 
Theory there appeared still another theory to explain 
why birds migrate. It was put forward by Professor Marek of 
Hungary and emphasizes the factor of barometric pressure as 
being of the greatest importance in determining the migratory 
movements of birds. Marek’s conclusions are entitled to serious 
consideration for they are based upon many years of painstaking 
investigations concerning the correlation between bird migration 
and barometric conditions. He began by comparing known migra¬ 
tions of the woodcock in Europe with the weather charts of the 
same dates and found that, aside from minor deviations, these 
birds migrate from anti-cyclonic areas of high barometric pressure 
to cyclonic areas of low barometric pressure. This coincides in 
general with the direction of the wind but Marek would not say 
that it is the wind which causes the movements of birds,—rather 
that both wind and migration are caused by the same conditions, 
namely, the proximity of two areas of unequal barometric pres¬ 
sure. During the winter the polar regions form an anti-cyclonic 
area of high barometric pressure with low temperature and clear 
air relatively free from moisture while in the tropics there is a cor¬ 
responding area of low barometric pressure with high temperature 
and much humidity. The prevailing winds are from the north 
because the air always flows “down hill” from high pressure areas 
to those of low pressure. When spring comes there is a relative 
shifting in position in the barometric maxima and minima. In 
the north the temperature rises, humidity, cloudiness and precipita¬ 
tion all increase and an area of low barometric pressure becomes 
gradually established while the reverse conditions are occurring 
in the south. The result is that southerly winds become the pre¬ 
vailing ones and, at the same time, birds who are extremely sensi¬ 
tive to barometric changes unconsciously begin their spring mi¬ 
gration. In the same way the fall migration is initiated by the 
shifting of the barometric maxima and minima. 
Irregularities in migration, such as remarkable flights of birds 
