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THE WILSON JOURNAL OF ORNITHOLOGY • Voi 124. No. 4. December 2012 
temperatures at Lawler Falls in southern Cali- 
tornia using Six’s maximum-minimum thermom¬ 
eters placed within 1 m of occupied nests and 
measured RH using a sling psychrometer posi¬ 
tioned within 0.5 m of active nests during the 
1985-1986 Black Swift breeding seasons. Am¬ 
bient temperatures near the nests ranged from 
11.0-20.5 C for nests at drier sites to 11.5-17 
C for nests at wetter sites, while RH near nests 
was highly variable with a range of 54-96% 
averaging 77% (Foerster 1987). Mann ( 1997 ) 
measured temperatures with a portable thermom¬ 
eter placed near the center of a cave at Lawler 
Falls occupied by Black Swifts during survey 
visits from 1990 to 1992. He reported tempera¬ 
tures within the cave fluctuated no more than 2 
C throughout the field season and readings 
taken at night and early in the morning differed 
only 1-2 C from those taken during the day 
even though external temperatures fluctuated 
daily by 10-20 °C; the actual temperatures were 
not reported. A few humidity readings at this 
same site early in the season ranged from 80 to 
90%; the values decreased as the summer 
advanced (Mann 1997). 
The objective of our study was to document 
microclimate parameters at Black Swift nests in 
Colorado, New Mexico, and California by quan¬ 
tifying temperature and RH values. 
METHODS 
Study Sites. We reviewed known active colo¬ 
nies to identify sites that were amenable for data 
logger placement, including accessibility with 
reasonable effort and nests that could be reached 
with aid of ladders. Colorado has 104 known 
occupied colonies. New Mexico has three, and 
California has -20. but most were unsuitable for 
inclusion because of colony remoteness or nests 
too high to reach. 
We placed 42 data loggers over a period of five 
breeding seasons (2006-2010) at one New 
Mexico and eight Colorado breeding sites 
levattons of these sites ranged from 2.231 to 
:“ 7 : "' 1 '“ ,| '* n 8 Foothill, Montane, and 
Subalp,„ e Hie Zones (Levttd el al. 2008). Data 
from these two states were analyzed together due 
to habitat similarity. We placed two data loggers 
for the entire 2009 breeding season a, Lawle? 
Falls the San Jacinto Mountains of southern 
California at an elevation of 1,620 m in mixed 
comfer forest (Foerster and Collins 1990) This 
was the most southern and western site from 
which we collected data (Fig. 1). 
Data Collection and Analysis .—We used Mi- 
eroDAQ Log Tag model HAXO-8 humidity and 
temperature recorders (MicroDAQ.com Ltd.. 
Contoocook. NH. USA) that are 86 8 54.5 x 
8.6 mm and weigh 35 g. Data loggers can be 
deployed inconspicuously in close proximity to 
nests to collect season-long data and arc useful for 
collecting temperature and RH values due to their 
small si/e, accuracy, durability, battery longevity, 
and case ol use. Specifications for the device can 
be found on the company’s website (MicroDAO 
20 J 2). 
We programmed data loggers to collect tem¬ 
perature and RH data every 4 hrs which produced 
three dusk to dawn and three dawn to dusk 
leadings, capturing representative samples of 
these values during each 24-hr period. Data 
loggers were positioned as close to nests as 
possible without disturbing nesting birds to obtain 
the most accurate data of the nest microclimate. 
\Ac placed data loggers in abandoned nests, 
immediately adjacent to active nests, or on ledges 
within 20 cm of nests. Reaching the nest was not 
possible in some instances. We secured data 
loggers in those cases within 20-125 cm of nests 
or at an accessible site we felt was representative of 
die nest microclimates for that colony. We placed 
data loggers prior to onset of the breeding season 
and retrieved them after the end of the breeding 
season at most sites. We deployed data loggers 
during one summer and retrieved them the 
following summer at sites which were inaccessible 
until alter the start of the breeding season due to 
deep snow or streams that could not be crossed. 
W e considered the potential for noise impacts 
u | he| ieve units placed near nests did not produce 
sufficient sound that would disturb swifts. The 
primary' crystal oscillator, according to the 
manufacturer, produces a sound of 32.768 Hz. 
ut the crystal is physically dampened by a 
si icone agent, further reducing sound production 
(MicroDAQ.com Ltd., pers. comm.). All birds can 
hear frequencies down to a minimum of —50 Hz 
with the upper limit of hearing at -20,000 Hz; 
cochlear potentials have been detected up to 
30,000 Hz by using greater intensities of .sound 
ih.in those normally encountered (Schwartzkopfl 
1955), 
We divided Colorado and New Mexico data 
into live chronological segments of the nesting 
season lor analysis based on breeding phenology 
