MIGRATION OF FISH. ' 141 



From these circumstances doubts have arisen whether 

 swallows migrate or lie dormant ; but there are so 

 many proofs of their migration^ that there is ground 

 to believe these deviations are only accidental. On 

 the approach of cold weather, they have been often 

 observed hovering on the sea-coast, as if waiting for a 

 calm, or a favourable wind, to waft them to their des- 

 tined port. In warm climates these tender birds re- 

 main stationary, because there is no cold to injure 

 them, or destroy the insects upon which they feed. 



Linna3us says, that the female chaffinches alone 

 leave Sweden in September, and migrate to Holland, 

 forsaking their mates till the return of spring ; a devi- 

 ation from the usual course for which it is not easy 

 to account. 



This extraordinary propensity to change their resi- 

 dence is not confined to birds ; fish and insects are 

 known to migrate at certain seasons. Shoals of her- 

 rings, cod, and haddocks, approach our shores at a 

 particular time of the year, and quit them with equal 

 regularity, without leaving a single one behind. 



Adanson, a celebrated traveller, relates, that near 

 the river Gambia, in Africa, about eight in the morning 

 in February, there suddenly arose over his head a thick 

 cloud, which darkened the air, and deprived him and 

 his companions of the rays of the sun. He soon found 

 that it was a swarm of locusts, raised about twenty 



