184 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 2. NO. 4. 
in winter, like the green woodpecker (18), but to take a definite 
direction, namely, to the south." 
He then shows that in the eider duck of Europe we have every 
stage from a migratory bird to one that is stationary, and we 
find it, therefore, in the Arctic zone a genuine migratory bird, in 
the Baltic only a wanderer, and in the North Sea a resident — ''a 
conclusive proof that migration and wandering are not essential 
characteristics of the species, but a habit which is adopted when 
the necessities of life require it, and a proof, moreover, that the 
regular migration has grown out of the irregular wandering in 
search of food." 
Much valuable work as well as much speculation has also been 
done on the question how birds find their way between their sum- 
mer and winter homes. The first careful investigations on this' 
subject were undertaken by Dr. A. von Middendorf, in 1855, and 
resulted in his well known work Die Isopiptesen Russlands (19). 
He found that the direction of migration in Russia is in general 
toward the north pole, and conceived the idea that birds must be 
endowed with a sixth sense, a magnetic sense of direction. Pal- 
men, a few years later, revealed Middendorf's error when he 
showed that the direction followed depends almost entirely upon 
the topographv of the countries through which the migrations ex- 
tend (20). The general belief then was that young birds are 
first led over a course by one or several older, experienced birds, 
and that through sight and memory these courses are followed 
year after year. The investigations of the older American orni- 
thologists seem to indicate that this is actually the case (21). 
Herr Gatke, however, seems to find from his extended observa- 
tions on Heligoland that it is not so there. He says innumerable 
flocks pass his station of observation year after year composed 
entirely of young birds (22). This subject has been the cause 
of much controversy among ornithologists and is still an unsettled 
question. Recent observations along this line show us nothing 
definitely one way or the other (23). 
18. Or like our waxwing, the tree sparrow, many of our hawks, and 
others. 
19. Die Isopiptesen Russlands. Mem. of the Imp. Acad, of Sc. of St. 
Petersburg, 1859. 
20. Palmen, Ueber die Zugstrassen der Voegel. 
21. Brewster, Bull. Nutt. Ornith. Club, No. 1, p. 15. 
22. Heligoland, An Ornith. Essay, 1895. 
23. Barrington, The Migration of Birds observed at Irish light-houses, 
1888-'97. Dublin, 1901; also Bailey, Proc. Del. Valley Ornith. Club, No. 
3, p. 13. 
