Biology Reference
In-Depth Information
house finches native to the eastern Rocky Mountains also expanded their
range northward into Montana in the period between 1940 and 1955.
The source of the house finches released on Long Island was southern
California, where the population is strongly sedentary, with only 2-3% of
birds showing seasonal movements of more than 80 km (Able and
Belthoff 1998). By 1960, substantial migratory movements were docu-
mented in New York State and Pennsylvania, and by the 1980s, long-dis-
tance movements of birds from northern states to wintering areas in
Florida and the Gulf Coast had developed. In contrast to southern Cali-
fornia birds, the movements of eastern birds were oriented in a northeast-
southwest direction. As the population of house finches spread outward
from the area of introduction, the distances of seasonal movement
increased markedly, suggesting that colonists of new areas were individu-
als tending to be more migratory in nature. Overall, however, the eastern
North American population is only partially migrant. The fraction of
birds moving more than 80 km between summer and winter is about
36%—much higher than in their southern California source area. Alto-
gether, the pattern of development of migratory behavior in house
finches of eastern North America is most consistent with the hypothesis
that selection has favored genetic traits related to migration. These traits
appear to have existed at low frequency in southern California popula-
tions, enabling rapid evolution of migratory patterns in the new eastern
populations.
Badyaev and Hill (2000) analyzed the general morphology of popula-
tions of house finches in several of these recently occupied regions and
compared them to long-established populations in California and Mex-
ico. They found complex, multidirectional patterns of evolutionary
change in bill, wing, tail, and tarsus length and body mass in newly estab-
lished populations. For example, Hawaiian birds changed little in many
factors but showed substantial reduction in bill length. Several populations
showed increased sexual dimorphism in one or more characteristics.
Alabama birds, for example, showed significant sexual dimorphism in all
five major characteristics, whereas California birds were dimorphic only
in wing and tail length.
In Montana, where house finch breeding activity was observed over
4 yr, Badyaev and Martin (2000) found that selection, judged by repro-
ductive success, was acting strongly on sexually dimorphic characteristics.
This result indicated that this newly established population was still evolv-
ing toward a morphology adjusted to the local environment. Additional
studies examined selection based on pairing success, fecundity, and over-
