A462 ' Remarks on the 
temperate zones at the approach of winter, 
to seek a better climate in lower latitudes. 
The migration of our summer visitors being 
established upon authentic facts, I intend to 
proceed in the next place, to give a theory of 
their annual motions derived from natural 
causes. All the birds constituting the migrat- 
ing’ tribe feed upon insects, which disappear 
and become torpid, either in a perfect state 
or under the form of embryos, soon after the 
autumnal equinox. This circumstance re- 
fuses the animals under consideration a far- 
ther supply of proper aliment in the higher 
latitudes. They are therefore compelled by 
tke apprehension of starving, to use their 
wings and retire southwards into more ge- 
nial climates, where the rigours of winter do 
not lock up the sources of their natural food. 
The manners of the winter birds of passage 
favour the last conclusion; for the jack-snipe, 
the red-wing, the woodcock, and the fieldfare, 
with some other species, quit the frosty re- 
gions of the north at the approach of cold 
weather, and spend the winter in the more 
temperate parts of Europe. But the return 
of spring admonishes them when to leave 
these countries; and they retire generally be- 
fore the end of April, to pass the breeding 
season on the confines of the arctic circle. 
