Ippietal. • BREEDING BIOLOGY OF THE SOUTHERN HOUSE WREN 
535 
Johnson 1998. Johnson et al. 2001). Skutch (1953) 
rcpoiieda 15-day incubation period fora resident 
population of House Wrens in Central America, 
similar to resident populations at 26 S 1 15.8 days; 
Aueret al. 2007) and 35 S latitude (14.8 days; 
Tuero et al. 2007). Fledging at our study site 
occurred at a mean of 16 days of age, within the 
range reported for different populations of North¬ 
ern House Wrens (14 to 20 days; Kendeigh 1941, 
Skutch 1953, Johnson 1998. Johnson et al. 2004). 
and slightly longer than the 14.8 days recorded for 
a subtropical population (Auer et al. 2007). This 
period is shorter than the 18-20 days described for 
Central American populations of House Wren 
(Skutch 1953. Freed 1987). 
Adult Body Size.—The Southern House Wren 
had little differentiation in body size between 
males and females. However, males had longer 
wings than females, similar to populations in the 
Northern Hemisphere, although beak and tail 
length are also greater in males in those popu¬ 
lations (Johnson 1998). The Southern House Wren 
appears to be slightly larger, particularly consider¬ 
ing that females (F) and males (M) have longer 
beak length (F: M = 13.9; 14.0 mm in Chiloe vs. 
il-8; 12.7 mm in Northern Hemisphere popula¬ 
tions). tarsus (F: M - 17.8; 17.9 mm vs. 16.8; 
17.5 nun), and tails (F: M = 43.7; 43.7 mm vs. 
40.8; 42.1 mm) (Johnson 1998). 
The Southern House Wren population on 
Chiloe Island has smaller clutch size, larger eggs, 
and a longer incubation period than populations of 
'he Nonhem House Wren at similar latitudes in 
(he Northern Hemisphere. Some hypotheses have 
invoked predation pressure, winter mortality, and 
migration to explain smaller clutch sizes in South 
American species (Ricklefs 1980, Martin et al. 
2000. Yom-Tov and Geffen 2002, Griebeler and 
Bobning-Gaese 2004). Martin (2002) proposed 
■he low rate of adult mortality in southern com¬ 
pared to northern passerines can explain smaller 
reproductive investment, such as reduced nest 
c are. which results in a longer incubation period 
and smaller clutch size (see also Ghalambor and 
Martin 2001. and Robinson el al. 2008). Nest 
attentiveness during incubation is lower, the 
incubation period is longer, and the total period 
°l parental care is longer for tropical and south 
temperate species than for their northern counter¬ 
parts (Russell et al. 2004. Chalfoun and Martin 
-907). hi contrast, the Hedging period is similar in 
Northern and Southern House wrens, but it is 
longer in Central America. The results of our 
study suggest that duration of the Hedging period 
decreases with latitude. Short nestling periods 
could be adaptive in high latitudes to synchronize 
brood rearing with maximum food availability 
(Lack 1947. Siikamaki 1998). improve survival 
rate of fledglings (Naef-Daenzer et al. 2001. 
Moreno et al. 2005). and/or avoid molting during 
breeding (Svensson and Nilson 1997). Our study 
highlights the effects that latitude can have on a 
species' breeding biology and the large geograph¬ 
ic variation that can occur in the breeding stra¬ 
tegies between populations of a single species. 
Data on variation in reproductive traits over the 
entire distributional range of the species are 
incomplete, because the Southern House Wren 
inhabits regions ranging to the southern extreme 
of South America. 
AC KNOW LK DG ME NTS 
The study was funded by grants FONDECYTs 1060186 
and 1090794 to RAY, grant CGL2004-00787/BOS to JM. 
travel grant CSIC-Univcrsidad de Chile 2003-2004-2009 
to SM. JM. and RAV. the 2004 BBVA Foundation prize in 
research on Conservation Biology, and the Institute of 
Ecology and Biodiversity (ICM-P05-002, PBF-23-CON- 
ICYT). Fundacion Senda Darwin kindly allowed us to work 
in Senda Darwin Biological Station, and Ines Hanning in 
Fundo ‘Los Cisnes’.. Child Andrea Gallardo. Rocio Jana. 
Ren6 Quispe. and Miguel Rodriguez-Gironcs helped with 
fieldwork. Ivlin Diaz. Gon/alo Farfan. Jose Iriarte-Diaz, 
Natalia Marquez. Danicla Parra. Ronny Zuniga, and Yuri 
Zuniga helped in making aiul/or putting up the nest boxes. 
Alvaro Rivera-Rei helped with statistical analysis. Com¬ 
ments by 1.. S. Johnson. W. F van Dongen, P. E. Llambtas, 
an anonymous reviewer, and the editor greatly improved a 
previous version ol this manuscript. The House Wren 
bibliography compiled by C. F. Thompson and L. S. 
Johnson facilitated our work. SI acknowledges support 
from a CONICYT scholarship. This is a contribution to the 
Research Program of the LTSER network at Senda Darwin 
Biological Station. Chiloe Island. Chile. 
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chronosequence in northern Chiloe Island. Chile. 
Revista Chilena de Historia Natural 75:339-360. 
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subtropical montane forest in northwestern Argentina. 
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Geographic gradients in body size, a clarification of 
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the birds of the world, with conservation status and 
