Vi. Introduction 
and its main tributaries, and a broad fringe of the northern sea, 
measuring at least ten miles from the coast. This is altogether 
a very clearly marked and well defined faunal area, and parti- 
cularly rich in its avi-fauna from the fact that off the mouth of 
the Humber the two main lines of the autumn immigratory 
flights converge and overlap—the first sweeping down from 
Scandinavia and north-eastern Europe, that is from north and 
north-east to south and south-west, and striking the east coast 
of Great Britain as far to the south as the north coast of Norfolk ; 
the second, and equally important, is known as the east to 
west route, and passes from south-east and east of Europe across 
the southernmost waters of the North Sea. 
The number of species included in the list is 322, and this is 
a very large record for so limited an area. These numbers in- 
clude first the so-called residents, that is, such species as remain 
in the country throughout the year. It is evident, however, 
that with few exceptions—the game birds and perhaps the 
green and lesser-spotted woodpeckers and nuthatch — these 
residents are, to a greater or less extent, migratory, and while 
some individuals, usually the old, remain, the greater portion of 
each species leave, and their place becomes occupied by others 
of the same sort presumably arriving from northern and eastern 
Europe. The term residents and partial migrants would there- 
fore better represent this large class than the more generally 
used term residents. 
Summer visitors are such as come in spring and leave in 
autumn, and winter visitors such as arrive in autumn and leave 
for the north in spring. A large class, principally geese, ducks, 
waders and seafowl, are the periodical visitors, which twice a 
year pass through the district to and from their northern breed- 
ing places, and these either pass directly to the south or remain 
for weeks and months within the area. 
Lastly, we have an extended list of rare and accidental visitors, 
some of which have only been recognised once and others barely 
half-a-dozen times. These represent wanderers from various 
and often very distant countries. 
