186 REPTILES AND BIRDS. 
under the intruder’s feet, in order to attract his attention from her 
progeny. 
When the young are matured, they abandon the family tie, and 
soon lose themselves in the great world of Nature, forgetful of their 
parents’ unselfish care. The ingratitude of their first-born does not, 
however, discourage the forsaken couple. With the returning season 
they renew their labours, exhibit the same solicitude, the same affec- 
tion, to meet with the same return. Nature is an unfailing source, 
an eternal focus, of tenderness and love. 
Most families of birds are migratory ; that is, they abandon their 
summer quarters and undertake long journeys at certain seasons. 
These migrations occur with the greatest regularity. By their 
departure from temperate or cold climates they prognosticate the 
approach of winter, as their return heralds spring. Among 
the ancient Greeks, as we learn from a passage of Aristophanes 
on Birds, the arrival of the crane pointed out the time of sow- 
ing; the arrival of the kite the sheep-shearing season; and the 
arrival of the swallow the date for putting off summer clothing. The 
impulse which causes birds to depart is an instinctive desire to 
find climatic conditions appropriate to their wants of life. At the 
approach of winter they desert the regions of the north in search 
of southern countries with a warmer climate, while others migrate 
northwards to escape the heat. 
Nevertheless, all birds are not migratory ; many species remain 
during their whole lives in the locality where they were hatched, 
straying but little from their birth-place. The majority of those which 
migrate perform their journeys annually and with great regularity ; 
a few of them irregularly and accidentally, that is, they do so by 
necessity, or are forced by atmospheric influences to change their 
residence ; and it is no unusual sight on such occasions to see 
numerous flocks of birds assembling under the leadership of a chief, 
and taking their departure. On the 22nd of September, 1771, 
White of Selborne witnessed the flight of a flock of swallows which 
had rendezvoused the night before in a neighbour’s walnut-tree. “ At 
dawn of what was a very foggy day, they arose altogether in infinite 
numbers, occasioning such a rustling from the strokes of their wings 
against the hazy atmosphere that the sound might be heard at a 
considerable distance.” In the Old World, choosing a time when 
the winds are favourable, most migratory birds direct their flight to- 
wards the south-east in the autumn, and the north-west in spring. In 
America the migratory birds take a southerly direction in autumn, and 
the reverse in spring. ‘These aérial travellers instinctively direct their 
