x ii INTRODUCTION. 



river. And all this is conducted with the greatest punctuality, and 

 the same may be said of their reappearance a few months later, 

 It is also a noteworthy fact, proved by experiments, that birds which 

 affect a certain station or district usually return to it year after year. 

 The question as to how they subsist during their migrations is readily 

 M>lvcd, when we consider the velocity of their flight together with the 

 considerable length of time the majority continue on the wing. If 

 we estimate the speed of a bird's flight at a mile in two minutes it 

 would need but 24 hours to carry it as many as seven hundred miles 

 without taking into consideration favourable wind currents which 

 would probably nearly double the distance. Red-starts and other short- 

 winged birds pass by gradual and slow movements as is evidenced by 

 their appearance in different countries at different times of the year 

 but these seldom go further than the inaccessible heights of moun- 

 tain ranges. Many journey during the night to avoid the dangers of 

 daylight or for the purpose of taking advantage of favourable air 

 currents. What the true reason for migrating is, has yet to be learnt. 

 We see their punctuality of departure and return, we note the dates 

 very carefully, the time of theix nidification, the composition of the 

 various structures they build for the rearing of their young, also the 

 number of eggs they lay, their colour, size and shape as well as the 

 changes of their plumage during the breeding season, but beyond this, 

 and conjecture, we have not gone. The nidificatibn of birds is indeed 

 very various, but in consonance with their habits. The high-flying 

 rapacious birds have their eyries on the ledges of high mountains in 

 the most inaccessible parts or on the tops of high trees ; the larger 

 ones, including the Vulturinae, lay but one, and seldom two eggs. The 

 lesser ones, as the Accipitrinae, build generally on trees, or on steeple 

 tops, and lay 2 4 eggs, and seldom do more than repair their nests 

 annually. All true vultures lay but a single egg, and their nests, as 

 are those of eagles, are built entirely of stout sticks and twigs with a 

 hollow receptacle lined with coarse grass or fine twigs and any soft 

 material. Bones also form a part of the structure. Many birds build 

 in society occupying trees, mountain ledges, plains, and the eaves of 

 roof as sparrows, crows, herons, gulls, terns; and some when robbed 

 of their eggs lay others very shortly after. The situation of the nests, 

 too, are quite in consonance with their habife of life. Owls build in 



