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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 1. March 2012 
wing and tail measurements that are within ranges 
for C. n. costarieensis, further highlighting the 
uncertainty of migration and winter distribution 
for this subspecies. Winter records for Northern 
Black Swift arc non-existent. 
Several factors contribute to the lack of 
knowledge about migration and winter distribu¬ 
tion of this species, including difficulty in 
accurate field identification of individuals due to 
high and rapid flight, problems differentiating this 
species from similar-size members of Cypseloides 
that occupy Central and South America, and 
inability to verify observation records. No band 
recoveries exist outside of the United States from 
~200 Northern Black Swifts banded from 1950 to 
present (Bird Banding Laboratory, pers. comm.), 
Currently, satellite tracking devices which 
provide accurate tracking of individuals are not 
sufficiently small to place on a species the size of 
Black Swifts. However, light-level geolocators, 
devices that record ambient light levels at fixed 
intervals, are highly effective instruments for 
tracking long-distance migratory species and are 
sufficiently small to place on swifts. They are 
battery-powered instruments with a microproces¬ 
sor, clock, and memory for data storage; geo¬ 
graphical positions can be calculated from the 
data collected by the devices. 
Geolocators must be retrieved to download 
data, and the Black Swift is particularly suited to 
recapture due to its high breeding colony fidelity 
and an individual propensity to reuse the same 
nest from year to year (Foerster 1987. Collins and 
Foerster 1995, Marin 1997, Hirschman et al. 
2007). We placed geolocators on four Northern 
Black Swifts with the objective to gather infor¬ 
mation about the migratory path, timing, and 
winter destination of this species. 
Identifying the connectivity of a migrating 
species between breeding sites and wintering 
areas is crucial to understanding the species' 
ecology and in guiding conservation efforts. Time 
spent in widely separated and ecologically 
disparate locations by migrating species and the 
strength of this link can have great biological 
consequences for individuals and populations, 
me uding reproductive success, population dy¬ 
namics, behavioral ecology, evolution, and re- 
^cctive pressures (Webster 
can nr' . ^Advances in geolocator technology 
ua"s a?h h r fol ™‘ ion by individ 
betause 'nf Ut,0n - Wc ‘-™*'ded this study 
because tnforntatton on migration and wintering 
areas of Northern Black Swifts was virtually non¬ 
existent (Lowther and Collins 2002, Wiggins 
2004). The small sample does not tell us how- 
weak or strong the migratory connectivity is for 
this subspecies, but forms a foundation for 
additional knowledge of this species' ecology 
and can guide future studies. 
METHODS 
Study Sites .—Northern Black Swifts nest at or 
near waterfalls typically inaccessible due to steep 
and vertical configuration (Knorr 1961. Levad 
et al. 2008). More than 100 breeding sites of this 
species have been documented in North America 
(Lowther and Collins 2002, Levad et al. 2008) 
with only a few records of alternate types of sites 
such as sea caves in California (Legg 1956). small 
cave-like boulder configurations in streams (Foer¬ 
ster and Collins 1990, Johnson 1990, Hurtado 
2002), and caves (Davis 1964, Northern British 
Columbia Caving Club 2003). 
We chose Fulton Resurgence Cave (39 49' N. 
107 24' W) and Ouray Box Canyon Falls(38 I' 
N, 107 40' W) in Colorado because of accessi¬ 
bility and the probability of capturing and 
recapturing Black Swifts using hand-held or mist 
nets. These breeding colonies are two of the 
largest in Colorado (Levad et al. 2008) with an 
average of eight nesting pairs (range 7-9, n = 
6 yrs) at Fulton Resurgence Cave (KMP, pers. 
obs.) and an average of 11 nesting pairs (range 7- 
15, n = 10 yrs) at Box Canyon Falls (Hirshman 
et al. 2007, Levad et al. 2008). Fulton Resurgence 
Cave is a limestone cave with a small stream 
issuing from it. forming a microhabitat conducive 
for a Black Swift breeding colony (Knorr 1961). 
Mist nets placed near the mouth of the cave, the 
only ingress/egress for swifts, have resulted in a 
recapture rate of 41% since banding of adults 
began in 2006 (KMP. pers. obs.). Box Canyon Falls 
is a popular tourist site and walkways provide 
views of the falls. The walkways allow access to 
several nest sites and. with the aid of ladders, 
several nests can be reached with hand-held nets. 
Data Collection .—We used four MklOS model 
geolocators, manufactured by the British Antarc¬ 
tic Survey (BAS), programmed to continuously 
measure light levels every minute and archive the 
maximum measurement for each 10-min period. 
The devices weighed 1.2 g, measured IS X 9 X 
6 mm, and have a light sensor mounted at the tip 
of a 10-mm stalk angled at 15 to prevent it from 
being covered by feathers. The instruments are 
