ON THE MIGRATION OF BIRDS. 4.73 
SEPTEMBER, during October, and early in November. These are the 
result of the identical weather-conditions which cause similar emigratory 
movements from northern Europe, except that the conditions favourable 
for emigration prevail over the British area and to the southwards, and 
do not extend northwards. Indeed, the movement is usually kept quite 
distinct from an immigration by the interposition of weather barriers to 
the north, which cut off migratory communication between our shores 
and those of north-western Europe. These barriers most frequently take 
the form of a subsidiary low-pressure area lying over the North Sea 
between Great Britain and Scandinavia. 
These great emigrations from Britain and Ireland, like the great immi- 
grations from northern Europe at the same season, set in on the passing 
away of the cyclonic conditions unfavourable for bird-migration, and on 
the prevalence of an anticyclonic, or fine weather, spell with its charac- 
teristic calm and cold. In this case, too, the unfavourable conditions 
which have passed away probably act as a warning to many laggards 
among the migratory birds, while the cold adds an additional spur and 
swells the ranks of the departing birds. 
During October movements are observed locally, which are directly 
traceable to the influence exerted on emigration by a considerable lower- 
ing of the temperature over a particular area. Thus, for example, on 
October 20, 1883, there was a remarkable movement of Swallows to the 
south-east coast of Ireland. On this day there was a decided fall in 
temperature, the lowest readings being recorded for Ireland, where these 
laggard summer-birds had until then found congenial quarters. 
Again, on October 10, 1885, a local movement to the southward 
of Thrushes and Blackbirds was recorded at stations in the north of 
Scotland, and in this instance, too, the meteorological data afford the 
information that a fall in temperature had occurred within that area. 
The emigratory movements in the late autumn and winter are, as has 
been already stated in this Report, attributable to the direct pressure of 
severe weather-conditions, in the shape of frost or heavy snow. It has 
been said, too, that these movements on the part of our resident and 
visitant birds are renewed with each outburst of cold, &c., during Novem- 
ber, December, January, February, and early March—in some years down 
to the third week of the latter month. Little more need be said regard- 
ing these simple weather influences on British bird-emigration. 
In certain years, however, the months of midwinter are characterised by 
conditions of Arctic severity. The January of 1881 was the most terrible 
month of the period covered by the inquiry. During its severe days many 
hundreds of birds perished even in the climatically most favourably 
situated portions of the British area—namely, the isles off the south-west 
coast of Ireland. The dominant feature of this month was intense cold, 
which for about three weeks reigned supreme.in all parts of the British 
area, and was accompanied by severe, harsh gales and heavy snow. 
Thus, in spite of an exceptionally warm period during the month, 
the mean temperature for this January was from 5° to 12° below the 
average. | 
Spring Immigration.—In connection with the spring immigration, 
two very remarkable instances occurred on February 17, 1887. On this 
day several Wheatears arrived at the Chicken’s Rock Lighthouse, and a 
Ring Ouzel was observed and shot at the Longship station. This date is 
exceptionally early for these species—indeed, they are the earliest records 
