1 86 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 aerial travellers instinctively direct their 



