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The Wilson Journal of Ornithology 124(41:797-802. 2012 
Nest Microclimate at Northern Black Swift Colonies in Colorado, New 
Mexico, and California: Temperature and Relative Humidity 
Carolyn Gunn . 1 1 Kim M. Potter , 2 and Jason P. Beason 3 
ABSTRACT.—The ecological nesting requirements 
of Northern Black Swills (Cypscloldcs ni^cr borealis I 
have been well documented, but little information exists 
regarding the microclimate at Black Swift nests. We 
placed 42 data loggers at 10 occupied Black Swift 
colonies between 2006 and 2010 to measure and record 
temperature and relative humidity, resulting in 19,181 
usable records. Median temperature and relative 
humidity at nine Colorado and New Mexico sites were 
,J -4 C and 89.7%, respectively, and at one California 
site were 13.4 C and 92.8%. respectively. Values were 
quite stable throughout the breeding season with slight 
changes reflecting the ambient temperature and humid¬ 
ity of the surrounding macroclimate. These baseline 
data may prove useful for conservation of this species, 
especially if predicted global climate changes occur. 
Received 6 February 2012. Accepted I June 2012. 
The microclimate at Northern Black Swift 
(Cypseloides niger borealis) nests is believed to 
he an important requirement for ncsl-site selection 
hut there is a paucity of information on temper¬ 
ature and, especially, relative humidity (RH) 
p. 0. Box 791, Dolores. CO 81323. USA 
’White River National Forest. Rifle Ranger District. U094 
County Road 244, Rifle, CO 81650. USA. 
Rocky Mountain Bird Observatory . P. O. Box 1232. 
Brighton’ CO 80601. USA. 
4 Corresponding author; e-mail: cgunn@tone.net 
(Lowther and Collins 2002). Knorr (1961) con¬ 
cluded Black Swifts occur only in isolated 
colonics with specific ecological criteria, includ¬ 
ing proximity to water, high relief over surround¬ 
ing terrain, inaccessibility to predators, little or no 
direct sunlight, and unobstructed fly ways. Levad 
et al. (2008) analyzed 291 potential nesting sites 
of Black Swifts and reported stream flow, 
availability of potential nest platforms, amount 
of moss, shading of potential nest niches, 
topographic relief of surrounding terrain, and ease 
of aerial access to potential nest niches each 
significantly contributed to a higher probability 
the site would he occupied by Black Swifts. 
Neither of these studies mentioned temperature 
and humidity, but low temperatures and high 
humidity arc common characteristics of all 
breeding sites for this species. Marin (1997) 
suggested cool temperatures at a cave occupied 
by Black Swifts could assist nestlings in main¬ 
taining a steady body temperature when adults 
were away from the nest. 
The first reference to temperature and humidity 
at Black Swift breeding sites was by Murphy 
(1951:448). who noted "considerable moisture” 
and temperatures as low as 0-1.1 C at an 
occupied colony in July 1949 near Silverton. 
Colorado. Foerster (1987) recorded ambient nest 
