PIED WAGTAIL. 
209 
seen on the southern coast, when none are to be observed 
inland, does not seem to have had any suspicion that they 
went still farther. 
Notwithstanding the migration in autumn of this species 
in numbers, as above described, many yet remain behind. At 
the present season, the middle of December, we have observed 
flocks of eight or ten fly towards the south-west, just before 
dark in the evening, not one flock alone, but so many that 
the aggregate must amount to several hundred individuals. 
These all fly at an elevation just above gun shot; and 
although being desirous of obtaining specimens, we walked 
some miles along the bank of the Thames for that purpose, 
not one specimen was to be met with, either on the ground or 
within the range of a gun. Whether these are now on their 
way to join their migrating brethren, and have stayed to this 
late period, in consequence of the unusual mildness of the 
season, or intend to pass the winter in these latitudes, future 
observation must decide. 
Towards the end of February, Pied Wagtails may be seen 
flying in pairs, having by that time chosen their mates for 
the summer. Some differences of opinion seem to prevail 
with regard to the plumage of the two sexes of this species at 
different seasons, some authors describing the female to have 
her back dark slate-grey, or grey mottled with black, and attri¬ 
buting to the Motacilla alba of Linneus alone, the pure grey- 
back, Our opinion on the subject rather differs from this, 
and an observation recorded some time ago in our own note¬ 
book, will, we believe, be found frequently correct, “ Feb. 
25, saw two Pied Wagtails flying together in pursuit from 
tree to tree, evidently a pair: one had the head and back 
perfectly black, of an uniform colour; the head and nape 
only of the other were black, the back clear, pale ash-grey. 
These birds, it may fairly be presumed, were about the same 
age ; why then does the back of the one become darker, and 
that of the other lighter in the spring season 
