222 WiLLARD 0)1 Migration of IVif/Zcr Birds. [J"ly 



We must acknowledge that birds do not differ so much from 

 other animals as not to have the custom of wandering. The 

 variation in the numbers of our resident species is due, to some 

 extent, to this natural habit, but can this alone be sufficient 

 to explain the movements of our northern birds? Do they breed 

 so late in the season that this flight is taken before the excitement 

 incident to their nesting has subsided, or do they leave their 

 northern homes merety from the ordinary passion for ^^•andering? 

 That there is a subtle incentive to migration inherent in these 

 species seems almost evident ; but is this impulse due to repro- 

 duction, or is it analogous to the impulse that urges our regular 

 migrants southward on the return of autumn ? The latter seems 

 to me the more plausible explanation ; for why should this move- 

 ment take place in the fall, or during the months of November 

 and December, if it were occasioned b}' a mere desire to wander? 

 Would it not be more natural to find these birds in southern lati- 

 tudes in September and October, if wandering was the only 

 incentive ? During these months the weather is cool and apparent- 

 Iv more conducive to long flights than the sharp, benumbing cold 

 of later months. But this is not the case. We find these birds 

 here just prior to or during the first genuine cold spell in the fail, 

 which, in Northern Wisconsin, usually occurs about November 

 20. The majoritv of these visitors appear to remain but a short 

 time, returning seeminglv to their northern latitudes, even though 

 the weather still continues cold. 



Bv a svstematic studv of the avian faima of Brown and Outa- 

 gamie counties,* I have found that the migratoi-y instinct is 

 represented in nearly all of its stages. We find birds that return 

 southward during the fullness of vegetation and abundance of 

 insect life : and species in which this instinct is not so well 

 developed, but which take their departure only when spurred 

 onward by the movements of other migrants, or the lowering of 

 the temperature. Still others are represented in which this 

 instinct is nearly dormant, and which seems only capable of 

 being aroused bv intense cold, such as usually occurs during the 

 appearance of the more noithern species in southern latitudes. 



At the time when the greater part of animal life was confined 



* In a paper read before the Wisconsin Academy of Sciences, Arts and Letters, at 

 Madison, Dec, 1883, I arranged the birds of these counties in classes according to 

 their migratory habits, and from this consideration I arrived at the conclusion given in 

 this article. 



