MIGRATION. 
399 
the Sea Eagle, which only occasionally leaves its 
breeding-place and wanders to the southward or west¬ 
ward ; the Goshawk and Sparrowhawk, the Snowy Owl 
and Hawk Owl, which visit us in most years ,* the Great 
Black Woodpecker, which still occasionally passes through 
localities where it has become almost extinct; the Pine 
Grosbeak, a rare visitor in Germany; Redpoles and 
Siskins; and, lastly, the Eider Duck, Razorbill, and 
Guillemot. All the remaining European birds which 
quit their homes are either true migrants or belong to 
the third class* of wanderers. 
We have not, as yet, received sufficient information, 
the result of observation, to enable us to determine, with 
any degree of certainty, the cause of the second descrip¬ 
tion of migration.! It is probable that those birds acting 
under its influence usually remain at home, where they 
find sufficient nourishment: with some species this can, 
however, scarcely be, and yet they are rare visitors with 
us. Sometimes a series of years passes, during which not 
a single bird of a certain species is to be seen in places 
where it had been formerly observed. My father remarked 
that during a period of forty years he never met with an 
authentic case of a Redpole in our part of the country: 
after this, however, they made their appearance in thou¬ 
sands, though only to vanish again as suddenly as they 
came; since which time they have never again honoured 
us with a visit. As yet, we are only certain of one thing, 
and that is that during a severe winter we are favoured 
with more northern visitors than in a mild one : beyond 
this we know nothing. “ The winter of 1847,” says my 
father, “was an extraordinary one: the Lesser Redpole 
made its appearance as early as October; and, later, came 
* German : Streiclien.— W. J. 
+ German : Wandern.— W. J. 
