410 Recently published Ornithological Works. [Ibis, 



Grinnell on limitations of distributional areas. 



[Field tests of theories concerning Distributional Control. By 

 Joseph Grinnell. Amer. Nat., New York, li. 1917, pp. 115-128.] 



In this thouglitfal article Mr. Grinnell discusses the 

 various factors which exert a control on the ranges of 

 various animals. Among these may he mentioned humi- 

 dity, temperature, food-supply, cloudiness, and of course 

 laud- and sea-barriers. He then takes the case of certain 

 selected birds and mammals, and endeavours to show what 

 factors have in each case limited their distribution. The 

 case of the Oregon Jay {Perisoreus obscurus), a close ally of 

 the Canada Jay or Whiskey Jack, is especially interesting. 

 This bird is only found in the northern parts of California. 

 Even there it is very local in its occurrence and absolutely 

 non-migratory. In the north-eastern part of the interior 

 of California it is found in the Warner mountains and on 

 Mt. Shasta, from about 7000 feet to timber-line, and is 

 unknown below that level ; but in the north-west along the 

 Pacific coast it re-occurs in the forests near the sea, but 

 here it rarely ranges higher than 300 or 400 feet above 

 sea-level, although there are mountains not far inland rising 

 to several thousand feet. 



After an examination of all the possible factors to explain 

 this curious anomaly, Mr. Grinnell came to the conclusion 

 that it is due to a cool summer temperature, which is very 

 marked on the Pacific coast, owing to the sea-breezes from 

 the ocean, and this approximates to the summer temperature 

 of the Warner and Shasta mountains at 6000 or 7000 feet 

 in the mountains of the interior,, while in the country 

 between the summer temperature is far higher. On the 

 other hand, the Avinter climate of the coastal area is of 

 course far milder than that of the mountains. In this case 

 there can be no question of humidity as Humboldt Bay, 

 the coast-locality, is the most humid and rainy area of the 

 State, whereas the Warner and Shasta mountains are 

 relatively arid. The critical factor therefore in this case 

 is summer temperature. 



