No. 2.] HOFFMAN ON THE BIRDS OF NEVADA. 207 



proper, the species thus far found bemg mentioned in the list under 

 their respective names. 



There are a number of species, resident during the winter in the 

 greatest depression of the northwestern portion of the State, which as- 

 sume a vertical migration during the summer, crossing the different zones 

 until they reach the cooler wooded summits of the mountains. The most 

 j)rominent examples aTQBegulus callendula and Certhia familiaris ameri- 

 cana. Species whose vertical range is very great, though not resident, 

 are Merula migratoria propinqua, Pyranga liidoviciania^ Picus villosus 

 harrisiy 8elasphorus platycercus, and Colapies auratus mexicanus. 



Over the arid deserts of the northern half of Nevada, three species 

 appeared common, viz, UremopMla alpestris chrysolcema, Zenidiira euro- 

 linensiSj and Corvus corax carnivorus. The occurrence of TrocMlus colu- 

 hris at an elevation of 9,700 feet (near the timber-line) is only consistent 

 with what has been stated before regarding the elevation and distribu- 

 tion of the several zones of vegetation as marking the limit beyond which 

 certain species of birds do not usually pass. In the tropics this species 

 has been detected at an altitude of 14,600 feet, the altitude of the same 

 zone, while its northern and southern migrations extend respectively to 

 latitude 61° and Tierra del Fuego. That certain species of birds extend 

 over a great vertical range in the tropics is well known, and this can 

 readily be attributed to the great altitudes at which the several zones 

 of vegetation are found in that region, which ascend from both the north- 

 ern and southern parallels of latitude, to which von Humboldt refers in 

 the following passage : " The great elevation attained in several tropical 

 countries, not only by single mountains but even extensive districts, 

 enables the inhabitants of the torrid zone to behold also those vegetable 

 forms which, demanding a cooler temperature, would seem to belong to 

 other zones. Elevation above the level of the sea gives this cool er temper- 

 ature even in the hottest parts of the earth, and cypresses, pines, oaks, 

 berberries, and alders nearly allied to our own cover the mountainous 

 districts and elevated plains of Southern Mexico and the chain of the 

 Andes at the equator."* 



The zones of vegetation characteristic of the upper portion of Mexico 

 occur in the tropics at altitudes corresponding to the mean temperature 

 of the former localities, which would place the outside limit of elevation 

 at about 10,000 feet. M. Becquerel says: "In the equatorial zone no 

 change is observed in the vegetation from the level of the sea to the 

 height of GOO metres (1,969 feet), and beyond this even to an altitude of 

 1,200 metres (3,937 feet) we still recognize the flora of the tropical zone." t 

 From the preceding remarks it will be observed that the absence of 

 birds in large areas of Nevada, and their abundance in certain locali- 

 ties, can mainly be attributed to the peculiar distribution of the vege- 

 tation. With the birds as with insects, particularly the Coleoptera, 



* Aspects of Nature, «fcc. Tr. by Mrs. Sabine. Philada., 1649, pp. 245, 246. 

 t Smithsonian Eeport, 1869, -p. 401. 



