332 
POPULAR SCIENCE REVIEW. 
speaking be called birds of passage, as tbeir numbers seem 
entirely dependent on the state of the weatber in Europe and 
local gales. The tree, meadow, red-tbroated, and tawny 
pipits cross and recross regularly, and often in large flocks. 
Tbe meadow-pipit is another illustration of a bird wbicb 
remains all tbe year in northern Europe, but is migratory 
in tbe southern parts. As soon as tbe hot weatber has fairly 
set in in Africa, flocks of tbe short-toed lark proceed to 
southern Europe and distribute themselves over wastes ; like 
other desert-living birds, it is very sensible of cold, and 
accordingly quits Europe before tbe regular migratory season. 
Tbe sky, crested, and Calandra larks go southwards late in 
October and tbe following month ; tbe two last-named are 
extremely abundant in north Africa during winter. Tbe wood- 
lark repairs to southern Europe during tbe winter, but a few 
also regularly push further southwards, and cross again in 
spring. Tbe pied wagtail and its northern variety, called after 
the late Mr. Yarrell, repair to southern Europe on tbe 
approach of winter, and many also cross tbe great inland sea 
and proceed a long way into Africa ; we found tbe former very 
common up tbe Nile to the second cataract. Tbe grey wag- 
tail, although nowhere so common, follows tbe same course 
and pushes northwards at tbe same time with its congener in 
spring. Tbe yellow wagtails of Europe have been so fre- 
quently confounded and misnamed, that until tbe student has 
carefully examined specimens of each be will be almost sure 
to become confused. There is, flrst, tbe yellow wagtail of tbe 
British Islands, called also Ray^s wagtail, that migrates to the 
Continent in winter, but we opine not to southern Europe ; 
this bird has been mistaken for tbe yellow wagtail of tbe 
Continent, flrst described by Linnaeus. Enormous flocks of 
tbe last-named bird cross regularly to and from Africa 
annually : probably not a straggler remains in either country 
after tbe migrator}^' seasons are over. We have repeatedly 
noticed varieties of this wagtail, with grey and black-coloured 
beads, wbicb many naturalists consider as speciflc difierences, 
whilst others appear to class them under tbe bead of a race 
or variety of the Motacilla flava of Linngeus. We are 
enabled so far to strengthen tbe latter opinion, by tbe fact 
that in a large series of skins collected from flocks of yellow 
wagtails during tbeir migrations across tbe Mediterranean, 
we could make out a gradual transition from tbe one state of 
plumage to tbe other, and we frequently found tbe grey, 
black, and olive-beaded (or yellow wagtail proper) all in one 
flock and constantly associating together, and with tbe same 
call-note ; tbe only difierence was tbe call-note in autumn in 
some was noticed to be harsher; these, however, we ascer- 
tained to be birds of the year. Tbe rook is migratory in 
