MIGRATIONS OF BIRDS. 391 



or the beginning of winter ; and in the first fine weather, avoid- 

 ing our heat, as they had done excess of cold, they return to lay 

 their eggs in the north. Other Birds, which are born in our 

 own country, and which may be considered as properly belonging 

 to it, quit us in autumn ; and after passing the winter in warm 

 climates, they revisit us in the spring, or perhaps, avoiding the 

 moderate warmth of our summer, they emigrate to Arctic regions. 

 Others again, natives of southern climates, come to the north to 

 escape from the ardour of a summer's sun ; and arrive in the 

 midst of our own fine weather. There are also some which 

 never remain in temperate countries, but merely pass through 

 them in their annual migrations. The time of the arrival and 

 departure of these travellers, is generally fixed definitely for 

 each species ; and experience teaches us that, in certain localities, 

 sportsmen may depend on the arrival of such and such Birds at 

 a given time, as certainly as on rent which is due on a regular 

 day. Age causes however some difference ; the young seldom 

 set out till after the old Birds ; this seems to arise from the 

 circumstance, that moulting taking place in them at a later 

 period; so that they are not sufficiently recovered from the 

 malady which attends this phenomenon, to endure the fatigues 

 of such a journey, at the time when the old Birds are ready to 

 undertake it. 



356. 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 direct 

 course to their nests. Carrier Pigeons afford a remarkable 

 example of this sense or instinct, quite incomprehensible to Man : 

 Swallows furnish another instance. 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 



