PERCHING BIRDS. 91 
Sometimes I have seen it used in such abundance as to 
form a mass more than half an.inch thick, slightly 
felted together. I have known of two very singular 
positions for the nest. One of them was underneath a 
rail on a colliery railway which was in constant use, the 
parent bird flying off on the approach of a train of coal 
waggons, and resuming her seat on her eggs when it 
had passed. The other was built in the bows of a ferry- 
boat, and though the boat was constantly passing back- 
wards and forwards, the young were successfully reared. 
The White Wagtail (IM. alba, Linn.) is I believe not 
such a stranger to our island as has been supposed. I 
have met with it several times, most frequently in the 
autumn and winter months. During the former season 
they have appeared in some years abundantly, while in 
the winter I have never seen more than one or two at a 
time. They were very numerous in September, 1854, 
frequenting the roads and margin of the stream running 
through the village. In January, 1855, during a sharp 
frost, and when the ground was covered with snow, I 
saw on two occasions a single bird in the street opposite 
my own house; it was busy searching the gutters in 
company with two or three of the pied species, and the 
distinction between the two was strikingly seen, the 
bluish ashen grey of the back of the white, contrasting 
strongly with the dusky colour of that part in the pied 
bird. 
The Grey Wagtail (I. boarula) generally visits us in 
the winter, though it is not common. I have met with 
it both in the neighbourhood of houses (my own couri- 
yard, for instance) and on the shallow parts of the 
stream, and in severe frosts I have even seen it wade 
into water as deep as it could bottom. It generally 
