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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 3. September 2012 
TABLE 3. Morphological measures (mean ± SD) of adult and nestling Southern House Wrens on Chilod Island. Chile. 
Mass (g) 
W ing imml 
Tarsus (mm) 
Tail (mm) 
Beak (mm) 
n 
Adult females 
Adult males 
Nestlings 
10.0 ± 0.5 
10.0 ± 0.5 
9.8 ± 0.6 
50.1 ± 1.5 
51.5 ± 1.5 
33.7 ± 4.2 
17.9 ± 0.9 
17.8 ± 0.6 
17.8 ± 0.8 
43.7 ± 2.6 
43.7 ± 1.8 
13.9 ± 1.3 
14.0 ± 1.1 
9.7 ± 1.1 
21 
17 
24 
clutch size, which agrees with Llambias and 
Fernandez (2009). In contrast. Northern House 
Wrens have larger clutches, and more nestlings 
and fledglings in artificial nest boxes compared to 
natural tree cavities (Purcell et al. 1997). 
The Southern House Wren on Chiloe Island has 
a smaller clutch size (mean = 4.3: range = 2-5 
eggs) compared to populations at the same 
latitude in the Northern Hemisphere (range of 
reported means = 6.0-6.5 eggs/clutch: Robinson 
and Rotenberry 1991. Quinn and Holroyd 1992. 
Elliot el al. 1994, Young 1994, Johnson 1998). 
This is still larger than in tropical (means between 
3.3 and 3.9 eggs/clutch: Freed 1987, Young 1994) 
and subtropical latitudes (3.5 eggs/clutch in 
natural tree cavities; Auer et al. 2007). although 
some authors have recorded as many as five eggs 
for tropical populations (Skutch 1953) and 4.7-5.2 
eggs/clutch at 35-36 S (Mason 1985. Tuero et al. 
2007, Llambias and Fernandez 2009). We did not 
detect any seasonal decline in clutch size (Finke 
et al. 1987. Robinson and Rotenberry 1991. Johnson 
et al. 2001). in contrast to Northern House Wrens. 
However, we had insufficient detailed data about 
possible second broods. There were positive 
associations between latitude and clutch size for 
both Northern and Southern House wrens, al¬ 
though clutch size and the range of latitudinal 
variation are smaller in the Southern Hemisphere 
(3.3 to 5.0 eggs vs. 3.3 to 7.1 eggs in the Northern 
Hemisphere: Young 1994). 
Egg and Nestling Size .—Mean egg size for the 
same clutch size is slightly larger on Chiloe Island 
than in the Northern Hemisphere (Kendeigh et al. 
1956: Table 4). The width and length of eggs of 
Southern House Wrens from Chiloe Island (13.2 
and 17.3 mm, width and length, respectively) are 
slightly greater than those in the Northern 
Hemisphere (12.7 and 16.6 mm: Johnson et al. 
2001, Styrsky et al. 2002), and similar to egg 
dimensions from Central America (13.4 and 
17.8 mm; Skutch 1953), subtropical .Argentina 
(13.4 and 17.0 mm; Auer et al. 2007), and 
southern Argentina (13.1 and 17.5 mm: Tuero 
et al. 2007). 
Southern House Wren nestlings reach an 
asymptotic growth after 10 days ol age. similar 
to wrens in Canada and Colombia (Zach 1982. 
Kattun 1996). No differences were found between 
mass of nestlings at 11 and 13 days in our popu¬ 
lation and mean weights were similar to those of 
Northern House Wrens from Manitoba. Canada 
(mean weights within 9.8-10 g: Zach 1982): these 
weights differed in comparison to House Wrens 
from Valle del Cauca, Colombia (mean weight 
within 14.5-15.5 g; Kattan 1996). However, 
tarsus, beak, and wing length differed between 
10 and 13 days, suggesting they were still growing 
at this time. The adult body mass of House Wrens 
from Colombia recorded by Kalian (1996) is 
striking as House Wrens at this location ha\e a 
much larger body size compared to other low 
latitude populations, contradictory to general 
predictions about increasing body size with 
latitude (Blackburn et al. 1999). 
Incubation and Fledging Period .—The incuba¬ 
tion period is slightly longer for Southern House 
Wrens on Chiloe Island (14 to 19 days: mean = 
16) compared (o Northern House Wrens from 
North America (9 to 16 days, mean = 12.6: 
TABLE 4. Mean ± SD width and length of eggs of Southern House Wrens from Chiloe Island. Chile vs. Northern 
House Wrens from Oh.o (40° N. Kendeigh el al. 1956) in nests of four and five eggs. 
Kendeigh et al. 1956 
Present study 
Mean width (mm) 
Clutch size 
4 5 
17.9 12.8 
J 3.3 ± 0.3 13.1 ±0.2 
Mean length (mm) 
Clutch size 
4 5 
16.8 16.6 
17.5 ± 0.8 17.5 ±0.6 
