268 
THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 2. June 2011 
93*30'0'W 93*20'0"W 93* 10*0 ”W 
probability of detection. We divided the number 
of active nests and failed nests at discovery by 
0.77 and 0.39, respectively; the average probabil¬ 
ity of detection estimates based on a 2-year study 
of EPP nest-searching methods. We calculated the 
95% Cl of estimates of the detection probabilities 
using the mean ± 2 SD (0.029 and 0.053 for 
active and tailed nests, respectively) as reported in 
Walter and Rusch (1997); and generated a 95% Cl 
for nest density in each year. 
Lemming Abundance .—We used relative lem¬ 
ming abundance estimated by Reiter and Andersen 
(2008b) lor Nestor One between 1992 and 2004 to 
identify years with lemming population peaks and 
