IS 



Birds — Our Living Resouncs 



Fig. 1. Geographic patterns in the 

 mean trends tor grassland bird 

 species during 1466-^2. 



Table. Percentage of species with 

 increasing populations for six 

 groups of birds having shared life- 

 history traits. The P value indi- 

 cates the probability that the per- 

 centage differs from 50%. 



which are significant incieases. Flycatcheis and 

 warblers have the largest proportions of species 

 with increasing populations. 



The percentage of increasing species within 

 each group of species having shared life-history 

 traits is sumniarized in the Table. The most con- 

 sistent declines are by grassland birds; only 

 1 8% have increasing population tiends. These 

 declines are most widespread in eastern Noilh 

 America, where few grassland species breed 

 (Fig. 1). Declining populations are also preva- 

 lent across the Great Plains, which includes the 

 breeding ranges of most grassland birds. The 

 pattern within western North America is mixed, 

 except for regions of declines along the Pacific 

 coast. 



A significant proportion of shrubland and 

 old-field bird species also exhibits population 

 declines (Table). As with grassland birds. 

 regions with declines are most prevalent in east- 



Negative trends 

 Positive trends 



Fig. 2. Geographic patterns in the 

 mean trends for shnibland and old- 

 field bird species during 1966-92. 



em North America as well as in the southern 

 Great Plains from Kansas and Missouri south to 

 Texas (Fig. 2). Shrubland species appear to be 

 generally increasing in western North America. 

 A majority of woodland bird populations is 

 increasing across most of the continent (Fig. 3). 

 Decreasing populations prevail in a few regions, 

 such as along the Appalachians from West 

 Virginia to northern Alabama, from Arkansas 

 across central Texas, and along the Pacific coast 

 from Oregon to central California. Woodland 

 birds, however, are increasing in more areas 

 than either grassland or early successional 

 species. 



Negative trends 

 Positive trends 



Fig. 3. Geographic patterns in the mean trends for wood- 

 land bird species during 1966-92. 



Neotropical migrants have received consid- 

 erable attention in recent years, yet as many 

 species have increased as have decreased during 

 1966-92 (Table). A region with apparently 

 declining populations extends from the southern 

 Great Plains across the southeastern states and 

 along the Appalachian Mountains to southern 

 New England (Fig. 4). Increasing mean popula- 

 tions prevail across the northern Great Plains 

 and throughout much of western North 

 America. The pattern of population decline in 

 the eastern United States noted by Robbins et 

 al. (1989) occuiTed after 1978 and is not reflect- 

 ed in these long-term trends. 



Short-distance migrants and permanent resi- 

 dents have slightly greater percentages of 

 decreasing species (Table). Both groups have 

 negative mean trends in the southeastern states 

 and from the lower Great Lakes into the 

 Appalachian Mountains, but the patterns else- 

 where are mixed (Figs. 5. 6). 



These results indicate that grassland and 

 shrubland birds are experiencing the most con- 

 sistent and widespread declines of any group of 

 species. Whenever possible, appropriate conser- 

 vation measures should be undertaken to 

 enhance the population trends of these species. 

 While the BBS data indicate the population 



