Dr. Jenner on the Migration of Birds. 95 



feed on the ground on worms and such insects as they can 

 find. Although repeated examinations of the contents of the 

 stomach have afforded the best proof of this, yet there is 

 scarcely any need of calling in its aid in the present instance, 

 as we may be convinced of the fact, by seeing them in flocks 

 feeding on the ground in open fields and meadows. I do not 

 deny their taking the haw and other vegetable food from the 

 hedges ; but they do it in so sparing a way, that I have re- 

 marked, that redwings and fieldfares died through hunger 

 during the long continuance of frosty weather, while the haws 

 on the hedges were by no means deficient. The occasional 

 departure of these and some other winter birds during a long 

 continued frost, must be very obvious. The greater number 

 disappear soon after its commencement, if it sets in very se- 

 verely: some few are always left behind and are soon starved, 

 if not fortunately relieved by a thaw. Those that are driven 

 to this necessitous migration, probably pursue a track that 

 quickly leads them out of the reach of frost. Of these flights 

 I shall produce instances, which render it probable that they 

 are able even to outstrip its course. 



The approach of intense frost is often to a certainty made 

 known to us by the appearance of a numerous tribe of water- 

 birds, some of which are rare, and seldom show themselves 

 here on any other occasion. We commonly see them three or 

 four days prior to the setting in of very severe frosty weather. 

 This was manifest at the latter end of the year 1794, at the 

 coming on of the severe season that ensued. In the river 

 Severn, about a mile and a half to the westward of this place, 

 were seen and taken many species of water-birds, that gene- 

 rally confine themselves to the more northern regions. Far 

 more pleasant is it to see during the continuance of hard forst, 

 the return of those birds which had left us at the beginning. 

 These are pleasant omens, and most certainly forebode a thaw. 

 The following example shows how soon they catch the first 

 opportunity of again seeking those countries from which they 

 were so lately driven by necessity. The day preceding the 

 thaw, the frost being then intense, a gentleman who was 

 shooting observed a large flock of fieldfares, birds that are 

 extremely common here in milder weather. They were as 

 much untamed as if no frost had appeared in our island. He 

 had the good fortune to shoot one of them, which was 

 brought to me. I found it as fat and plum]), and in every 

 respect in as good condition, as if it had remained here undis- 

 turbed, and had found provision in the greatest plenty, though 

 it was without ;i particle of food in its stomach. Its last meal 

 was digested; and the frost still remaining, it could find no 



food 



