306 INSECTIVOILE. 



useful to man, as the number of insects which they capture, 

 if allowed to remain and breed, would make the waters rank 

 and the land unsightly. 



As the wagtails subsist wholly upon insects, they are 

 unable to pass the winter months in the northern and ele- 

 vated parts of the country, because the ground is frozen up ; 

 but even there they may be found among the discharges of 

 those copious and deeply-seated springs, which maintain 

 nearly a uniform temperature all the year, and thus keep 

 their rivers open, even when the rest of the ground is skirted 

 with snow and ice. In such situations, the wagtails may be 

 seen even in the month of January, hopping under the banks 

 of snow that have been undermined by the discharge of the 

 spring. The change in the under part of the male bird to 

 white, is an adaptation of the bird to cold, in consequence of 

 which there is no doubt that they could bear the climate, 

 and only change their residence in order to find food. Many 

 of them retire to the sea-coasts, where they may be observed 

 running along the beaches, after the tide has ebbed, and 

 picking up the small marine animals that are left on the 

 sand. They linger long also about those fields where turnips 

 are fed off by folded sheep ; and may be seen there in con- 

 siderable numbers after they have all left their summer 

 haunts by the upland brooks. 



In the southern counties of England, they remain nearly 

 stationary all the year round ; and though, in many other 

 places, they leave their summer quarters, the probability is 

 that they only disperse to more suitable places, and do not, 

 in any great numbers at least, leave the country. It is true 

 that, in the north, they are not seen inland from the time 

 that the cold weather sets in till the storm breaks ; but as 

 that takes place a month sooner in some seasons than in 

 others, without any alteration of weather in the south ; yet 

 as the birds visit the northern brooks as soon as they are 



