Table 16-7. (Concluded) 



Species 



1971 



Index of Relative Abundance 



1972 1973 1974 1975 1976 1977 



Common yellowthroat 

 American redstart 

 Bobolink 



Eastern meadowlark 

 Red-winged blackbird 

 Northern oriole 

 Common grackle 

 Brown-headed cowbird 

 Rose-breasted grosbeak 

 Purple finch 

 American goldfinch 

 Rufous-sided towhee 

 Savanna sparrow 

 Chipping sparrow 

 White-throated sparrow 

 Song sparrow 



Christmas Bird Counts 



Wintering population trends of terrestrial birds are more variable than 

 breeding populations. Weather severity, seed crops, small mammal populations, 

 snow cover, breeding success, and fall migration patterns contribute to this 

 variability. Many seed-eating and raptorial species occur on a cyclical or 

 irregular basis corresponding to availability of food supplies on their 

 breeding grounds. Invasions of northern seed-eating finches are synchronous 

 throughout the U.S. in years of seed failures in the arctic and sub-arctic 

 (Bock 1976). 



People influence the local abundance of wintering birds by planting fruit- and 

 seed-bearing plants, and by providing bird feeders. About 16 species of semi- 

 hardy bird species are able to winter in Maine because of food provided at 

 bird feeders (table 16-8). 



The Audubon Christmas Bird Counts assess the relative abundance of birds 

 during late December. These counts are inherently variable in both count 

 effort and observer expertise, however, much of this variability can be 

 removed by standardizing the counts and only comparing counts conducted during 

 consecutive years. Evidence from an independent census method suggests that 

 results from Christmas Bird Counts reflect real population trends, but they 

 overemphasize roadside and urban birds and underestimate dispersed woodland 

 species . 



16-23 



10-80 



