No. 602] SHORTER ARTICLES AND DISCUSSIONS 



111 



of food is not likely, therefore, to be a controlling factor in its 

 distribution. 



The bird is a forest dweller. Its equipment as regards man- 

 ner of flight and course to take in case of attack by enemies is 

 adjusted to a forest habitat, and nowhere within the writer's 

 knowledge does this jay extend its range beyond the limits of 

 woods of some sort. Although somewhat predaceous itself, it 

 has regular enemies among hawks and owls, for protection from 

 which it makes use of forest vegetation. This factor of forest 

 cover, then, must be counted as essential. But the range of the 

 bird is not continuous wherever "forests extend. 



In the interior of California it does not descend below a cer- 

 tain altitude. Now three other factors in its distribution are 

 quite obviously connected with that of altitude, namely, baro- 

 metric pressure, atmospheric density, and temperature. But 

 when we take into account the fact that the Oregon jay exists 

 at or close to sea level around Humboldt Bay, the first two fac- 

 tors, those of pressure, and air density, are instantly elimina^ted, 

 because of the obvious fact that the bird successfully maintains 

 itself in localities of widely differing altitude where these factors 

 are thus extremely diverse. 



With reference to temperature, we know without recourse to 

 instrumentation that there is a decrease upwards at an average 

 rate of 3 to 4 degrees F. per thousand feet. If, then, the bird 

 is limited downwards at a critical point, the inference appar- 

 ently follows that temperature is the determining factor, and 

 this conclusion is inevitable if we consider only Mount Shasta 

 and the Warner Mountains. But the bird's occurrence at Hum- 

 boldt Bay complicates the problem. In order to reconcile these 

 facts of distribution we must look into the situation with refer- 

 ence to season. On doing so we discover that the home of the 

 Shasta and Warner jays is subject to severe winters with heavy 

 snow, very much colder than the winters at Humboldt Bay, 

 where the climate is equable and snow rarely falls. But the 

 summer temperature at Humboldt Bay is well kno^vn to be much 

 cooler than that of even somewhat higher regions in the interior, 

 up to an altitude of at least 4,000 or 5,000 feet, because of the 

 eastward moving air-currents, which are coolest where they first 

 leave the sea surface and warm up as they pa.ss farther and far- 

 ther inland. We are therefore led directly to the final inference 

 that the summer temperature at sea level about Humboldt Bay 



