THE "ORDER OF THEIR GOING." 
S6 
may suppose that the course of the journey is indicated to those 
young birds who have had no experience of it, and that preliminary 
excursions are taken to test their strength. .Finally, a cold night 
comes, followed by a touch of frost; the time of departure has 
arrived ; and on the next bright morning the swarms rise high 
above the trees, and set out on their adventurous course. 
Migrations similar to those at which we have glanced are observ- 
able also in the southern hemisphere. The birds of Nortli America 
wing their way southward as far as Brazil ; those of South Australia 
towards the north of the great " island-continent " and the neighbour- 
ing islands, — as, for example, New Guinea. 
Before setting out, the migratory birds, as in the case of the 
swallows, are accustomed to assemble at certain places, and when 
their numbers are sufficient they take their departui'e. Some 
exercise themselves before entering on their long journey; test their 
physical energies against those of their companions, — with whom, 
not unfrequently, they engage in mimic strife. 
The migrating swarms keep together moi'e or less closely during 
the voyage. Occasionally they assume, in flying, a compact and 
regular array. The reader will remember the lines of Milton which 
describe the winged phalanx of the cranes : — 
" Part, more wise, 
In common, ranged in figure, wedge their way, 
Intelligent of seasons, and set forth 
Their aery caravan, high over seas 
Flying, and over lands, with mutual wing 
Easing their flight ; so steers the prudent crane 
Her annual voyage, borne on winds; the air 
Floats as they pass, fanned with unnumbered plumes." 
Not a few kinds sail through the air in closed-up rank and file, while 
others scatter into irregular groups. Generally, they keep at a 
very considerable elevation; but at intervals they allow themselves 
to fall abruptly, flying for a time quite close to the ground, and then 
rising again to their former altitude. The feebler species do not 
venture on long flights, but pass only from tree to tree, from forest 
