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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 3. September 2011 
(Snow 1962, Rowley and Orr 1965, Collins 1968, 
Ayarzaguena 1984, Mann and Stiles 1992, Marin 
1999). Species of Cypseloidinae typically nest in 
caves and caverns, often on cliffs or vertical 
surfaces in close proximity to. or behind water¬ 
falls (Lack 1956. Knorr 1961, Rowley and Orr 
1965, Collins 1968. Whitacre 1989. Marin and 
Stiles 1992, Marin and Carrion 1994, Marin 
1997a). Rowley and Orr (1965) first described 
the nesting pattern of S. zonaris in Mexico, and 
most of comprehensive reproductive studies for 
this species are from Central America (Whitacre 
1989, Marin and Stiles 1992). Relevant available 
studies in South America describe the global 
aspects of its reproductive biology (Nehrkom 
1899, von Ihering 1900, Ruschi 1979, Marin 
1993). 
There is a lack of information about S. zonaris 
particularly in Argentina. Most published records 
are distributional notes and nest descriptions (De 
la Pena 1982. De Lucca 1989, Bianeucci 1995, 
Miatello et al. 1999). This species has been well 
documented in northern and western Argentina 
(Dabbene 1918, Olrog 1979, Dc Lucca 1989). and 
is known to occur in central and eastern Argentina 
(Narosky and Yzurieta 1987). S. zonaris is best 
documented in the Province of Cdrdoba (Pergo- 
lani 1944, De la Pena 1982. Narosky and Yzurieta 
1987, Yzurieta 1995, Miatello et al. 1999) at the 
‘La Cueva de los Pajaritos’ colony, where many 
swifts occur (Narosky and Yzurieta 1987. Yzur¬ 
ieta 1995). No current long-term study has been 
conducted on the reproduction of S. zonaris. The 
objectives of my study were to: (1) contribute to 
the general knowledge of the reproductive biology 
of swifts, and (2) delineate the breeding chronol¬ 
ogy of the White-collared Swift in Argentina. 
METHODS 
Study Area .—The Province of Cordoba occu¬ 
pies much of central Argentina at the confluence 
of many areas with different physiognomy and 
taxonomic lineages (Bucher and Abalos 1979). 
This region is in the Distrito Serrano Chaqueno 
(Chaco Province) with a semiarid climate influ¬ 
enced mainly by the Sierras Grandes (Cabrera 
(1976). These conditions relate to the rugged 
topography, insulation, and humidity, as well as 
the type of substrate and vegetation (Miatello et 
al. 1999). Low temperatures and northerly winds 
occur from June to late August, often associated 
with drought. Rain occurs mainly in summer 
ranging from 800 to 900 mm between October 
and April (Miatello et al. 1999). The study site is 
known as “La Cueva de los Pajaritos' and is at 31 
18’ S. 64 34' W, 869 ni asl. 
Field Work and Data Analysis .—The study site 
was subdivided into four different areas along 
natural limits of die relief configurations: Gar- 
ganta del Diablo’, ‘Cabeza del Indio', “Cueva de 
los Pajaritos’. and “Liuvia del Amor’. Fieldwork 
was conducted for 6 consecutive months from 
October 2001 to March 2002. I made 18 visits, 
each 2 days in duration, three times each month, 
at —8-day intervals. 
Nest searching was conducted during each visit 
considering the variability of the encounter rate 
throughout the reproductive period (Ralph et al. 
1996). Date, location, and place of settlement 
were recorded for each nest. Nests were recorded 
in the order in which they were found and were 
monitored at 0630-0930 and 1700-2000 hrs. The 
number of adults, eggs, and/or chicks present in or 
near the nest was recorded, and data on the 
physical appearance of nests were collected. I 
measured timing and duration of egg-laying, 
incubation, hatching, nestling, and fledging peri¬ 
ods and, when necessary, these dates were 
calculated as averages between visits. The repro¬ 
ductive period of S. zonaris was calculated from 
first egg-laying until last fledging, considering the 
activity of all nests (Marin 1999). Length of 
incubation and nestling stages was estimated 
following Foersler (1987). 
RESULTS 
Nests .—Six nests of S. zonaris were found in 
three of the four subareas of the site, all in close 
proximity to water (Table 1). Nests were placed 
on horizontal or slightly inclined surfaces on the 
vertical walls of the cliffs. All sites were relatively 
inaccessible with three in small cracks of the walls 
and three on extended prominence platforms. 
Most nests had a well-defined shape, typically a 
circular plate’ with a central depression. The 
exceptions were semicircular nest S5 and nest S6 
that did not show evident material and which were 
too small to have a specific shape. Total or partial 
absence of nesting material was also recorded ut 
nests (n = 2) inside “La Cueva de los Pajaritos 
Nesting material was principally semi-wet mud 
mixed with varying amounts of living plants 
(mosses, pteridophytes), and roots of macro¬ 
phytes. Nesting material was drier in nests (/? * 
3) in ‘Cabeza del Indio’ and ‘La Cueva de los 
