72 



The Canadian Field-Naturalist 



[Vol. XXXVI 



established limit to the density of population. 



By the first, the uncertain and finely adjusted 

 thread upon which some of our species depend for 

 continuance is shown and a possible cause is 

 suggested of the sudden disappearance of such of 

 our birds as the Labrador Duck, Passenger Pigeon, 

 Eskimo Curlew and others for which the human 

 element does not offer an altogether satisfactory 

 explanation. 



The recovery of the species from almost nothing 

 to practical normality within half a decade is an 

 indication of how quick and positive is the increase 

 in numbers to be expected from an adaptable 

 race when unfavorable conditions are absent. 

 The Bluebird always suffered somewhat from the 

 small boy and slingshot or flobert rifle combina- 

 tion, the zoologist enthusiast, the collector and, 

 at that date, the millinery trade to some extent. 

 But it shows that in spite of a handicap not amount- 

 ing to systematic human persecution, a species in 

 harmony with its environment tends to increase 

 rapidly. The converse is also suggested, that 

 species not particularly interfered with by man 

 and yet scarce are so because they lack harmony 

 with their environment and are probably already 

 on the road to natural extinction. We know that 

 species have arisen, flourished and decayed since 

 the beginning and long before man appeared on 

 the scene. Undoubtedly others are undergoing 

 the same process today independently of either 

 the direct or the indirect influence of man. Unless 

 through some fortunate insight into the involved 

 interaction of obscure cause and eifect man can 

 control some of the critical destructive factors, 

 most of these species are doomed to ultimate 

 extinction, irrespective of the human attitude. If 

 the Passenger Pigeon had been as well adapted 

 to modern conditions as its near relative, the 

 Mourning Dove, it would not have vanished 

 so suddenly and completely after the last great 

 rookery at Petoskey, Michigan, when all accounts 

 show that there were still hundreds of thousands 

 of birds remaining. The systematic netting and 

 hunting on a large scale ceased with this rookery, 

 and had the birds been fitted to survive there was 

 plenty of stock remaining to have persisted in- 



definitely, at least in moderate numbers, not- 

 withstanding occasional, irregular or sporadic 

 shooting. 



The third lesson taught by this Bluebird episode 

 is the demonstration that there is a saturation 

 point of population for each species beyond which 

 its numbers may not increase. Bluebirds rose 

 from practically nothing to their normal num- 

 bers in a few years a7id then they stopped short. 

 It was a remarkable demonstration of the law 

 of Malthus that a population tends to increase 

 at a geometrical ratio to the full supporting 

 power of the land. What factor it is that pre- 

 vents its indefinite increase cannot be guessed at 

 with any likelihood of success. Here was a 

 species increasing regularly and rapidly and 

 then, when a certain density of population was 

 reached, there came, without any apparent change 

 in controlling conditions, a sudden dead stop and 

 an indefinitely continued stationary population. 

 As far as we can see, there was no reason why a 

 growth of numbers should be shown in 1896 and 

 not in 1902. We can only acknowledge that there 

 is a factor of control that prohibits an indefinite 

 increase of population. 



The points I wish to make are: 



1. That species may be subject to sudden 

 unexpected factors of extinction that human fore- 

 sight cannot estimate, guard against or control. 



2. That strong dominant species have remark- 

 able resources of recovery from depletion which 

 will come into play if the cards are not stacked 

 against them. 



3. That a species unadapted to prevailing con- 

 ditions is doomed to slow or rapid extinction in 

 spite of all man can do to prevent it. 



4. That there is a certain density of population 

 for each species relative to the individuals of 

 that species and to competing forms beyond 

 which, under constant conditions, it is impossible 

 to increase. 



All these things should be considered and weigh- 

 ed and given their due importance in such con- 

 servation methods as we may put into force. 



SUMMER BIRDS OF THE LAC LA BICHE AND FORT McMURRAY REGION 



By F. M. Farley, Camrose, Alberta 



OF the many portions of western Canada that 

 have received little attention from orni- 

 thologists, perhaps none are more outstanding 

 than that country lying between Lac la Biche and 

 Ft. McMurray, at the junction of the Clearwater 



and Athabaska rivers. This part of Alberta lies 

 between the 55th and 57th degrees of latitude and 

 the 110th and 112th degrees of longitude, being 

 about eighty miles from east to west and one 

 hundred and forty miles from north to south, 



