.334 NORTHERN ZOOLOGY. 



but he observes that it disappears, together with the rest of the Swallow tribe, 

 in the middle of August. Hearne remarks that the Martins, though common in 

 the southern parts of Hudson's Bay, seldom go so far north as Churchill. The 

 whole history of the migratory birds proves that the main object of their wan- 

 derings is the obtaining a supply of proper food for themselves and their young. 

 All quarters of the fur-countries abound in the winged insects that Swallows 

 delight to feed upon ; but, owing to the large bodies of ice which hang upon the 

 northern shores of Hudson's Bay until the beginning of August, every breeze 

 from the sea, which sweeps the neighbouring country, produces a depression of 

 temperature sufficient to chill the insects and drive them to shelter ; the supply 

 of food to the Swallow tribe, consequently, in that district is so precarious as to 

 render the rearing of their young difficult and uncertain. In the interior of the 

 country, however, the case is different. When the snow is gone, the earth 

 speedily becomes heated ; and while the summer lasts, the temperature of the 

 atmosphere continues higher than the hottest weather that is ever experienced in 

 the insular climate of Britain, fostering incredible multitudes of mosquitoes. We 

 observed thousands of these Sand Martins fluttering at the entrance of their 

 burrows near the mouth of the Mackenzie, in the sixty-eighth parallel, on the 4th 

 of July ; and it is probable, from the state of the weather, that they had arrived 

 at least a fortnight prior to that date. They are equally numerous in every 

 district of the fur-countries wherein banks suitable for burrowing exist ; but 

 it is not likely that they ever rear more than one brood anywhere north of Lake 

 Superior. The eggs of this species measure 17 T V lines in length. — R. 



DESCRIPTION, 



Copied from Wilson ; no specimen having been brought to England by the Expedition. 



" The Bank Swallow is five inches long and ten inches in extent ; upper parts mouse- 

 coloured [hair-brown] ; lower white, with a band of dusky brownish across the upper part of 

 the breast ; tail forked, the exterior feather slightly edged with whitish ; lores and bill black ; 

 legs with a few tufts of downy feathers behind ; claws fine, pointed, and very sharp ; over the 

 eye a streak of whitish ; lower sides of the shafts whitish ; wings and tail darker than the 

 body. The female differs very little from the male." — The yearling birds have their feathers 

 bordered with rust colour. 



