610 THE POPULAR SCIENCE MONTHLY. 



ing very different families, live chiefly, and for the most part exclu- 

 sively, on the fruits ; a thing that would not be possible in a temperate 

 climate, where the development of the fruits is limited to a small part 

 of the year. The immense northern pine-woods of the Old and New 

 "Worlds have their denizens from the bird- world living exclusively 

 upon their seeds in the cross-bills, which are quite as much tree-birds 

 as the tropical parrots. 



The abundance of grains, fruits, insects, and even of mammalia, such 

 as mice, is, on account of the varying local weather conditions on which 

 they are dependent, much more variable in temperate than in tropical 

 regions. One year may be rich in these products, and the next very 

 poor ; unusually favorable conditions for their growth may prevail for 

 the time in one locality of an extensive territory, while in neighboring 

 districts, from causes which it is often hard to explain, the contrary 

 may be the case. Such circumstances must, of course, act with great 

 effect upon the bird-world. At some times the birds of a region may, 

 on account of the failure of their principal food and consequent fam- 

 ine, be driven from their hereditary quarters, and compelled, becoming 

 wanderers, to resort to districts that are strange to them. "When the 

 pine-nuts fail in the north and on the mountains, the nut-crackers that 

 feed upon them, obeying necessity, and not doing according to their 

 custom, come south ; and, when it is a bad year for birch-seed, multi- 

 tudes of the northern linnets visit Europe. During long, snow-bound 

 winters these northern and northeastern birds may be seen abundantly 

 in Germany, and away down in Southwestern Europe, and the super- 

 stitious countrymen see in the unusual visitors the heralds of coming 

 disasters. 



On the other hand, an unusual abundance of food attracts birds into 

 places to which they are not accustomed, and leads them into strange 

 companies. Naumann relates that the thistles once got so firm a hold 

 in the pasture-lands near his home that in many places the previously 

 luxuriant grass wholly disappeared ; then there came great flocks of 

 green-finches, attracted by the abundance of their favorite food, and 

 more in the next year at the time of the ripening of the seed, till, in 

 a few years, all the thistles were exterminated through the agency of 

 these birds. In another place he tells of a pine-woods of only thirty 

 acres, to which hundreds of cuckoos resorted, attracted by the enor- 

 mous number of caterpillars. It has also been frequently observed 

 that horned owls are to be found by the thousand in localities that 

 are plagued by an unusual visitation of mice. 



Numerous birds attach themselves to droves of wandering animals. 

 The passage-falcon travels regularly with the birds of passage ; schools 

 of herring are accompanied by throngs of fish-eaters, especially by the 

 -.timet, the presence of which is regarded by fishermen as the surest 

 indication of the neighborhood of herring. So, swarms of locusts, 

 pressing toward the West, are attended by birds to which they are 



