32 PHILOSOPHY OF ZOOLOGY. 



and the martin before the corncrake. Among the win- 

 ter birds of passage, similar differences in the time of 

 arrival are observable. Thus the woodcock precedes the 

 fieldfare, and the fieldfare the redwing. The periods of 

 departure have not been observed with such attention, 

 as the subjects have then lost their novelty, so that we do 

 not readily perceive their absence. It is probable, how- 

 ever, that in their departure, as well as their arrival, each 

 species has its particular period. 



The periods of arrival and departure, even in the same 

 species, do not always take place at exactly the same day, 

 or even month of the year. In different years these vary 

 several weeks or even months, and evidently depend on 

 very obvious circumstances. The meanest rustic, in regard 

 to the summer birds of passage, is aware, that cold weather 

 prevents the arrival of these messengers of spring; and 

 that the early arrival of our winter birds of passage indi- 

 cates a proportionally early winter. The same circumstan- 

 ces of temperature which retard our summer visitants also 

 check the progress of vegetation. Hence, in all probabili- 

 ty, we might be able to prognosticate the arrival of these 

 birds, by attending to the time of the leafing or flowering 

 of particular trees or plants. As the state of vegetation 

 depends on the temperature of the season, and the life of 

 insects on the state of vegetation, we may safely conclude, 

 that the movements of the phytivorous and insectivorous 

 birds must be dependent on the condition of plants. 



LINN^US bestowed some attention on these connected 

 circumstances, in his Calendar of Flora for Sweden ; and 

 STILLINGFLEET in that of England. LINNAEUS observed, that 

 the swallow returned to Sweden when the bird-cherry came 

 into leaf, and when the wood-anemone flowered. He also 

 found the arrival of the nightingale accompanied with the 

 leafing of the elm. STILLJNGFLEET says, that the swallow re- 



