to breed. It seems quite impossible to discover any reason for the diiTereiice in 

 the migration of these closely allied forms. Failure of food cannot be the cause 

 of the early migration of the Wilson Thrush, for at no time in the year are in- 

 sects and wild fruit more aibundant than in August and September; nor can it 

 be attributed to cold, these two months being the warmest of the year. The same 

 difference is found between the Xighthawk and the V\'hip-Poor-Will. These birds 

 are much alike in everything and would seem to lie adapted to the same conditions, 

 yet the Whip-Poor- Will remains here for a month or five weeks after the Night 

 Hawk has gone, the bulk of the Nighthawks leaving about the end of August. 

 Among the shore birds (Plovers and Sandpipers) the difference in the time of 

 their departure is still more noticeable, many species commencing their southern 

 migration early in July and leaving us entirely by the beginning of September, 

 wthile closely allied forms do not appear here until October and remain until the 

 first hard frost. Instances of this difference l)etween closely allied species may be 

 found in so many groups of our birds as to render it certain that neither failure 

 of food supply nor unfavourable climatic conditions can be accepted as the imme- 

 diate influence which governs migration in all species. 



When the spring migration from the south northward is studied the differ- 

 ence in method and range between allied species and of individuals composing the 

 species is very great. Among the warblers are some interesting examples of vari- 

 ation in the extent of migration. The Yellow Warbler, Black-throated Green 

 Warbler, Black and White Warbler, and some others, winter south of the United 

 States. On their return they do not travel far before tliey l)egin to select summer 

 quai'ters and they breed from the southern states all through their range to ISTorthern 

 Ontario. The Magnolia, Myrtle, Blackburnian, and Black-throated Blue Warblers 

 winter in the same region as the others, but they pass over the United States en- 

 tirely and with few individual exceptions go to the north of this province before 

 nesting, while the Blackjwll Warbler undertakes a most extended migration, the 

 equator and the Arctic Ocean being the extreme points of its journeys. The same 

 difference in extent of migration of the species is to be found in almost every group 

 of our land birds. Not only is there a groai diifercnce in the extent of the migra- 

 tion of allied species, but in certain cases some of the individuals ^v^hich compose 

 a generally migratory species never migrate at all. The common Bluebird affords 

 an example of this peculiarity. All through the southern states the Bluebird is a 

 resident, its numbers in the winter being increased 'by migrants from the north. 

 At the approach of spring they gradually s])read out from their base, working 

 northward as the season favors theui until they reach the limit of their range; 

 which, by the way, has been considerably extended as the land has been brought 

 under cultivation. All over the area from the Gulf of Mexico to Northern Ontario 

 and Southern Manitoba the Bluebird finds suitable breeding conditions and so do 

 other species. Why then do birds incur the perils involved in migration? As 

 winter comes on in the north we know that they must leave that region, or the 

 intense cold and failure of food would destroy them, but that does not explain 

 the spring movement at all, for we see that niauy indiviiluals of migratory species 

 find the climate conditions and food supply of the south perfectly suited to their 

 requiremenfs. I can only infer that, as T have said, the impulse, to migrate is an 

 express provision for the dispersal of birds over the eartli during the period when 

 their services are most required for the maintenance of the balance of nature. This 

 impulse is undoul)tedly hereditary in regularly migrant species, for youno- liirds 

 brought up from the nest in captivity always become possessed of a s]nrit of rest- 

 Icssnesss during each flight season, particularlv at uij^bt. 



