Enderson etui. • PEREGRINE FALCON NESTING PERFORMANCE 
129 
Work in each state was independent, and there 
were differences in how we selected sites to 
minimize bias in our sampling. A major portion of 
all known sites in Montana was studied each year. 
The 15 USFWS randomly selected sites were 
studied in Wyoming in 2006 and 2009 plus 
five others in each of three regions (Yellowstone 
National Park, east of the Continental Divide, 
and west of the Continental Divide). Randomly 
chosen sites substituted for the USFWS sites in 
the other years. About one third of the 27 USFWS 
designated sites in Colorado were studied each 
year in addition to many other sites near the 
USFWS sites or along routes to those sites. 
We also searched cliffs where no peregrine had 
ever been reported. These cliffs were not selected 
randomly or systematically, and most had been 
previously searched for peregrines. We used the 
saute techniques ms at selected sites. The extent of 
these searches varied by year and by state. 
We studied between 78 (/i = 83) and 96% (n = 
119) of all nest sites known at the beginning of each 
season in Montana plus sites discovered opportu¬ 
nistically in a survey year. We studied between 33 (n 
' 29) and 85% (n = 64) of all nest-sites known in 
Wyoming including subsets of randomly selected 
sites in three geographic regions. We studied 
between 20 (n = 21) and 30% (n = 44) of all sites 
known in Colorado at the beginning of each season. 
Occupancy and Reproduction. —Nesting local 
ities were observed at least once early in the 
nesting period (1 Apr-15 May) to locate active 
territories, defined as areas containing a nest 
"ithin the home range of a pair (Steenhof and 
Newton 2007). We made at least one other visit 
s Jun-30 Jul) to territories to document 
^productive success. Additional visits were made 
w ben earlier observations were inconclusive. We 
considered adult behavior and the condition and 
Sundance of excrement, and searched possible 
^maie sites before interpreting each nesting 
'Maiion. We met the requirements of the USFWS 
"Mnitoring protocol (USDl 2003). We returned a 
* COnd day for further searching if no peregrine 
'as seen after 3-5 hrs of steady viewing. We 
considered a site vacant when no peregrine was 
J ien in several hours of observation on each ol at 
,easl 2 days. Peregrines may have been over- 
'siked causing us to erroneously declare the site 
• acant when it was not; the occupancy rates we 
re Port may be minimum values. 
Nest-sites, usually cliffs, rocky outcrops, or tall 
river banks were observed with binoculars and 
spotting scopes at distances of 200 m to 1.5 km 
but for best viewing, we sought to observe from 
300-500 m, which was sufficiently close to hear 
peregrines yet provided a broad view. We did not 
climb to nests. The authors were the principal 
field observers, and each had more than 30 yrs of 
peregrine nest survey experience, mainly in their 
respective regions. Other competent observers 
( Acknowledgments) made <10% of all observa¬ 
tions. 
Reproduction rate was defined as the mean 
number of young of an assigned age produced by 
all pairs on territory where nesting outcome was 
ascertained (Steenhof and Newton 2007). We used 
28 days of age, following the USFWS monitoring 
protocol. Counts of young on the ledge, or after 
fledging were made when all young were seen 
simultaneously, or when other young, temporarily 
out of view, could be taken into account. Young 
may still have been overlooked and our reproduc¬ 
tion values may be minimum estimates. 
RESULTS 
Increase of Recorded Territories .—Discovery 
of cliffs with new pairs occurred each year in 
all states (Table 1). We searched 11 cliffs in 
Colorado with no record of peregrines and two 
had pairs. Other workers involved in wildlife 
studies reported 11 pairs at newly used cliffs, 
2005-2009, and also found tw'o pairs at long- 
vacant historical sites. We tound 18 new pairs 
in Wyoming including seven by follow-up checks 
on reports from others, seven by helicopter in 
wildlife surveys, and four by casual checks ol 
likely cliffs. We did not count all cliffs examined. 
Wc searched 50 historical sites in Montana vacant 
through 2004 and found pairs at 11. Additionally, 
33 pairs were found in other searches and through 
casual reports. 
Occupancy Rate.— The percent of nest-sites 
studied that were occupied by a pair ot 
peregrines (occupancy rate) varied between 75 
(Montana in 2009) and 100% (Wyoming in 
3 years) (Table 2). Annual occupancy rates in 
each state had a range of ~ 10%, and the 5-year 
means for each state differed by nearly as much. 
In no year was the number of surveyed sites 
fewer than 27 in any state. No trend in occupancy 
rates was apparent. 
Nest Success.— The percent of pairs that 
produced at least one young (success rate) where 
nesting outcome was known usually varied 
over the years in each state by <10% (Table 3). 
