; Beissinger 



Chapter 37 



Population Trends Projected from Demographic Analyses 



recruitment or decreased adult survivorship should be apparent 

 : by examining year-to-year changes in population size. 

 Increases in juvenile ratios coupled with increased population 

 size should indicate increased productivity. However, if 

 coupled with decreased population size, increased juvenile 

 ratios would indicate decreased adult survivorship. 



For making sound conservation decisions based on 

 population trends and demography, there is no substitute for 

 good field data based on direct estimates of population change, 

 survival and fecundity. For the Marbled Murrelet, such 

 information is likely to remain scarce. Future research should 

 explore the strengths and weakness of using the ratio of 

 juveniles to after-hatch-year birds as a proxy for direct 

 demographic measurements. 



Acknowledgments 



I am grateful to John Kelson, Irene Manley, S. Kim 

 Nelson, C. J. Ralph, and Craig Strong for permitting me to 

 include their data on juvenile ratios. Tom Hamer provided 

 me with the murrelet fledging dates, and Nadav Nur graciously 

 permitted me to use his analyses of auk survival rates in this 

 paper. I benefited from many discussions of these ideas and 

 of murrelet biology with Esther Burkett, Harry Carter, Blair 

 Csuti, James Gibbs, Tom Hamer, Mike Horton, Gary Miller, 

 S. Kim Nelson, Nadav Nur, David Perry, C. J. Ralph, and 

 Scott Stoleson. Reviews by Jon Bart, Kevin McKelvey, 

 Martin Raphael, E. Rexstad. and Robert Taylor helped to 

 improve this paper. 



USDA Forest Service Gen. Tech. Rep. PSW-152. 1995. 



393 



