294 THE REASON WHY : 



" The bird that hath been limed, with trembling wings mis- 

 doubtetii every bush." S 



of a summer's sun ; and arrive in the midst of our own 

 fine weather. 



There are also some which never remain in temperate climates, 

 but merely pass through them on their annual migrations. The 

 time of the arrival and departure of these travellers is generally 

 fixed definitely for each species, and in many instances may be 

 calculated upon to a day. 



94.5. Another fact not less curious in the history of birds is the power by which 

 they direct their course in unknown countries, and distinguish at immense 

 distances the immediate vicinity of their nests. Swallows furnish a remarkable 

 instance of this. . These little birds make very long journeys at the time of 

 migration ; and yet, by a singular instinct, they know, in the following spring, how 

 to find again the places where they had formerly established themselves, and 

 always return to them. This fact has been ascertained by attaching to the feet of 

 several swallows small silken threads to establish their identity. They build their 

 first nest near that in which they were born ; the chimney-swallow makes its nest 

 every year above that of the preceding year, and the house-swallow establishes 

 itself in that which it had quitted the autumn before. Indeed, it has been known 

 for the same couples to repair to their old nests, almost without taking the trouble 

 to rf-pair them, for eighteen years consecutively. Swallows show on other occa- 

 sions, also, a singular power of directing themselves towards a particular place from 

 which they are at a considerable distance. If a hen that is sitting is carried to a 

 distance, confined in a cage, and liberty afterwards given to her, she first rises to a 

 considerable height, as if to reconnoitre the country, and then flies in a straight 

 line to the spot where she has left her brood. 



946. Jfhy do birds when flying in flocks settle themselves into 

 a triangular body ? 



Because the position so assumed is the one best fitted to cut the 

 air with the greatest ease and rapidity. 



In this mode of flight, the leading bird, which divides the air in 

 advance of the others, has the most arduous post ; and in order to 

 obtain relief, the bird occupying this place goes to the rear after a 

 certain time, and is succeeded by another. 



947. Wliy do birds which take long flights usually fiy high ? 

 Jt is supposed that high flight is less fatiguing, owing to a 



