Our Living Resources — Birds 



19 



Negative trends 

 Positive trends 



Fig. 4. Geographic patterns in the mean trends for 

 Neotropical migrant bird species during 1966-92. 



trends for breeding birds, these data are not 

 designed to identify the factors responsible for 

 these trends. To understand how bird popula- 

 tions are responding to the changing habitat 

 conditions in North America, additional studies 

 are needed that would combine the BBS results 

 with regional data on land-use changes, weath- 

 er conditions, and other variables. 



References 



ESRI. 1992. Understanding CIS; the Arc/Info method. 

 Environmental Systems Research Institute, Inc.. 

 Redlands.CA. 416 pp. 



Geissler, P.H., and J.R. Sauer. 1990. Topics in route-regres- 

 sion analysis. Pages 53-56 in J.R. Sauer and S. Droege, 

 eds. Survey designs and statistical methods for the esti- 

 mation of avian population trends. U.S. Fish and Wildlife 

 Service Biological Rep. 90( 1 ). 



Isaaks, E.H., and R.M. Srivastava. 1989. An introduction to 

 applied geostatistics. O.xford University Press, New 

 York. 561 pp. 



Peterjohn. B.G., and JR. Sauer. 1993. North American 

 Breeding Bird Survey annual summary 1990-1991. Bird 

 Populations 1:52-67. 



Negative trends 

 Positive trends 



Rohbins. C.S., D. Bystrak, and PH. Geissler. 1986. The 

 Breeding Bird Survey: its first fifteen years, 1965-1979. 

 U.S. Fish and Wildlife Service Resour.Publ. 157, 196 pp. 



Robbins, C.S., JR. Sauer, R.S. Greenberg, and S. Droege. 

 1989. Population declines in North American birds that 

 migrate to the Neotropics. Proceedings of the National 

 Academy of Science USA 86:7658-7662. 



Sauer, JR., and S. Droege. 1990. Recent population trends 

 of the eastern bluebird. Wilson Bull. 102:239-252. 



Fig. S. Geographic patterns in the 

 mean trends for short-distance 

 migrant bird species during 1966- 

 92. 



Fig. 6. Geographic patterns in the 

 mean trends for permanent resi- 

 dent bird species during 1966-92. 



Appendix. Population trends of 

 birds from the North American 

 Breeding Bird Survey. To appear 

 in tJiis list, the species must have 

 been seen on > 40 routes at an 

 average count of > 1 bird/route. 

 We present trends (%/year), proba- 

 bility (P). and the number of 

 routes on which the species was 

 seen. See Peteijohn and Sauer 

 1 993 for group classification. 



