BIOLOGICAL TRADITIONS 



had built their nest off the ground on Artemisia plants. The birds came back 

 year after year and built the same kind of nests, until the habitat was de- 

 stroyed. It is extremely unlikely in this case ( and many similar ones ) that 

 some sort of mutation had occurred which resulted in the changed habit. 

 It is much more likely that one bird started the new fashion and others 

 learned' from him, until the entire population had acquired' the new habit. 

 Such new habits are usually lost as quickly as they are acquired, unless 

 they add measurably to the survival value of the species." On the Delta 

 Marsh, the Redhead usually nests over water in emergent vegetation, but 

 some few individuals nest on dry land, sometimes quite far from water, in 

 situations where one would expect to find Mallards. I have found such land 

 nests of Redheads in loose groups, with more than one in the same restricted 

 area. This looks like traditional nesting behavior. 



Nice (1943:150) decided that in the Song Sparrow, the pattern of song 

 "is innate, but the quality may be imitated. Particular songs may be impro- 

 vised, or may be adopted from some other Song Sparrow." Mayr (1942:54) 

 says that "it has been known to the field ornithologist for a long time that 

 in some birds the song varies from district to district. . . . The most re- 

 markable geographic variation of song and call-notes that has been de- 

 scribed occurs in the European Chaffinch. Promptoff (1930) called attention 

 to the fact that this species tends to break up into a number of geographic 

 song races. Sick (1939), who gives a general survey of the literature on 

 geographic variation of song, found that the so-called 'rain-call' of the Chaf- 

 finch is subject to an even more remarkable localization. This call, whose 

 exact biological significance is still somewhat obscure, is uttered by the 

 male within his breeding territory. In the township of Stuttgart, southern 

 Germany, three sharply characterized rain-calls occur, of which one is re- 

 stricted to the three-hundred-year-old park which extends along the valley 

 floor for a distance of three kilometers. The second call is restricted to the 

 hills to the west, and the third to the hills to the east of the town. A 'hybrid- 

 zone' is found where two of these dialect districts meet, but distributional 

 barriers, such as railroad yards, prevent such hybridization in other places, 

 so that districts of pure call notes approach each other occasionally within a 

 distance of only five hundred meters. Much circumstantial evidence indicates 

 that these call notes are not genetically fixed, but conditioned. The young 

 Chaffinch learns these call notes from his father and from the neighboring 

 males and he either stays at or always returns to the locality where he was 

 born. The exact history of the parks of Stuttgart is known, and it is evident 



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