326 
POPULAR SCIENCE REVIEW. 
southern winds occasionally beckoning them to advance^ they 
soon gain the object of their desires. Thus flocks may be 
seen pursuing their journey, and picking up a livelihood and 
more companions as they speed their way over mountain, 
moor, held, city, or sea to the sunny chmes and eternal sun- 
shine of Southern Europe and trans-Mediterranean lands. 
The majority of migratory birds cross the latter sea during 
the vernal and autumnal equinoxes ; whilst a few, such as 
certain finches and water birds, make their appearance on the 
islands and southern shores throughout the winter ; the latter, 
however, are in a great measure dependent on the state of the 
weather, and their numbers increase or decrease accordingly. 
It is evident that such animals as the lapp, lemming, musk 
ox, or reindeer must push southwards on the approach of 
winter. Their migrations are by no means unexpected ; nor 
would the mere land journey of birds create amazement when 
we know the real causes ; but to cross the great inland sea 
anywhere, save at its entrance, must be considered a great 
feat when performed by tiny warblers, and birds not physically 
adapted for long flights ; for instance, the willow warbler or 
the land-rail, crossing the broadest parts of the Mediterranean, 
must traverse at least 600 miles. No doubt the heated winds 
from the desert exert a great influence in determining the 
route to be taken by migratory birds, especially in the coun- 
tries that come directly under their operation; and at no 
seasons are their presence more apparent than during spring 
and autumn ; for not only then do they blow with their greatest 
violence, but are also most keenly felt by contrast with the 
previous hot or cold months. Thus the winds that beckon the 
bird in autumn to come southward, drive it back again to 
Europe in spring. Much, however, depends on the constitu- 
tional powers of the individual species, which vary greatly 
in members of the same family : for instance, the little chifi"- 
chafip often makes its appearance in England as early as the 
middle of March, whilst its congener, the willow warbler, is 
seldom seen before the end of April ; the spotted fly-catcher 
and night-jar arrive towards the end of May, and -depart again 
early in September. Bird migrations may be said to be either 
complete or partial : some birds totally abandon Europe during 
winter, and take up their residence in North Africa ; others 
repair merely to the more genial climates of the south of 
Europe ; whilst many remain, but in diminished numbers, 
throughout the year, the majority resorting »to milder tem- 
peratures. For example, the swallow tribe leave Europe 
entirely; the wagtails have their winter homes among the 
oases of the desert and on the banks of the Nile, whilst a few 
tarry in Southern Europe, and with their brethren in spring 
push northwards. A good m^ny stone-chats spend the winter 
