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THE WILSON JOURNAL OF ORNITHOLOGY . Vol 123, No. 4. December 2011 
FIG. 1. Eggs of the Pectoral Sparrow (Arremon tacitumus) in the foothills of Manu National Park, Cusco. Peru. 
wings and flanks. The nestling gained on average 
2.53 g per day between days 3 and 11. It weighed 
28.4 g on day II, the eyes were completely open, 
and the body and wing feathers opened further 
revealing olive and yellow coloration. Further 
measurements were not possible because the nest 
was empty on day 12. presumably due to 
predation. No tarsal measurements were taken 
for tlus nestling. Two chicks hatched from a 
second nest on 9 November. Their eyes were 
closed at hatch, the body was naked except for 
tme black down on the back, the interior of the 
mouth was bright red. and the beak was yellow 
" e i ghed 3 2 and 2 6 8 had a tarsus 
length of 5 and 6 mm. respectively. On duv I they 
weighed 5.4 and 4.1 g and had tarsus lengths of 6 
and 7 mm. They gained mass at a rate of 2 2 and 
1.5 g per day. respectively. The nest was empty on 
day the nest camera revealed an unidentified 
marsupial depredated the nest during the night. 
The male provisioned the nestlings on 16 
occasions over a 3-day period at the first nest, 
the lemale on five occasions and, in 10 cases, it 
was not possible to identify the gender of the 
parent We recorded three events when the male 
ted the female while she was brooding the 
nestlings during day 4 after hatching. The food 
was too small and mashed for recognition in most 
cases; however, in three instances it was possible 
o observe what appeared to be insect parts. The 
male continued to provide most of the food to the 
Sz ( r 76%) - afk ' r t,K fe ™ ie ‘Cd 
brooding. Removal of fecal sacs was solely by ,he 
None of the 15 nests was successful. N in e nests 
were depredated during the egg period, two during 
the nestling period, and four were abandoned for 
unknown reasons a few days after we started to 
monitor them. We made efforts to minimize nesi 
disturbance, hut observer interference cannot be 
ruled out as the reason for abandonment. 
Incubation .—The longest incubation period 
recorded was 15 days. The laying date was 
unknown for this nest, hut we believe the eggs 
were laid 1 or 2 days before being found since no 
embryo development was observed. Thus, the 
incubation period is likely between 15 and 
17 days. The female was the sole incubator based 
on our observations, photographs, and videos. 
The female had few but long absences each da) 
(Fig. 2). On average the female conducted 74 
trips per day (range = 4-10 trips, n - 18 da)'*' 
Average trip length was 46.4 min (n = 18 day 
The longest absence from the nest was 263 m 11 
while the shortest was 6 min. On average, die 
female spent 57% (range = 20-65%. n = 18day 
ol daylight incubating the eggs. The onTw UI 
periods ranged from 8 to 323 min with an average 
of 71.7 min (n = 18 days). The female >pen' ,he 
night incubating in all nests, except for ;:,i 
instance, when the female spent the night outside 
the nest. 
The female spent on average (- SD) 1,1 - 
3.7% of daylight incubating between days J ^ 
10 in the nest that lasted 15 days with tn f 
longer than 60 min. In contrast, the female spe nl 
55 ± 1.6% of daylight incubating between day 
11 and 14 before hatching and 20% ol trip s ' uU 
>60 min. Thus, females decreased on-nest 1 
before egg hatching by 6 ± 1.3%, when 12* 0 
the u-ips lasted >1 hr. 
