Astie and Luchesi • CREAMY-BELLIED THRUSH REPRODUCTIVE SUCCESS 
135 
J3 
(A 
® 
C 
*- 
0 
L. 
0 ) 
n 
E 
3 
2 
Period 
FIG I. Number of nests in the laying stage during the reproductive season of the Creamy-bellied Thrush. The 
reproductive season was divided into intervals of 10 days. 
aied with time in the season when the nest was 
initialed: nests that failed or succeeded (0-1) were 
independent of the time when they were initiated 
(logistic regression: X 2 = 1.03, P = 0.31, n = % 
nests). 
One egg was laid per day and incubation started 
w itli laying of the penultimate egg (for nests 
found during building and laying stages, n = 08). 
tgg survival was 0.67 ± 0.03 (/» 48 nests), 
hatching success was 0.74 ± 0.03 (n ® 109 nests), 
and fledgling survival was 0.87 ± 0.04 (n = 44 
nests). The number of eggs present in the nest did 
n '« affect egg survival or hatching success (X 2 = 
m P = 0.09, n = 48 and X 2 = 0.12 ,P = 0.94, 
11 ' 109, respectively), hut the number of 
ffstlings was negatively associated with fledgling 
success (X 2 = 16.35. P = 0.001. n = 44). At least 
■he nestling died when there were three nestlings 
"'58% of the nests (/? = 12 nests), at least one 
nestling died in 20% of the nests (n = 15 nests) 
' lien there were two nestlings, but only 4% died 
" = 17 nests) when there was one nestling. 
Bonfenoni correction for multiple com- 
P^isons set the significance level at y. < 0.005. 
Dai| .v nest mortality was higher during laying 
(0 -079 ± o.(K)6. n = 39) than during early 
,nc ubation (0.013 ± 0.002, n = 50, X 2 , = 8.77, 
^ ~ 0.003), but there was no difference with late 
inc ubation (0.017 ± 0.002, n = 53, X : i = 4.62, 
■ D ~ 0.041), early nestling (0.11 — 0.006. n = 50, 
= 2.13. P = 0.11), and late nestling (0.10 ± 
1-013, n = 24, X 2 , = 4.40, P = 0.022) periods. 
We found no differences between early and late 
incubation (X 2 = 1.09. P = 0.27) nor between 
early and late nestling (X 2 ! = 1.02, P - 0.28) 
periods. Early incubation was significantly lower 
than early and late nestling periods (X 2 , = 37.66. 
P < 0.001 and X 2 , = 45.99, P < 0.001, 
respectively), and late incubation was also 
significantly lower than early and late nestling 
periods (X 2 , = 37.54, P < 0.001. and X 2 , = 
45.14, P < 0.001, respectively; Fig. 2) 
We had small samples for parental care 
behavior and could not perform any statistical 
comparisons. Wc observed a trend of increased 
latency to return to the nest during the laying 
stage. Frequency of visits appeared to be highest 
during the nestling stage and time spent in the nest 
was highest during the incubation stage (Fig. 3). 
DISCUSSION 
The Creamy-bellied Thrush in the southern 
temperate Monte Desert has several characteris¬ 
tics typical of tropical birds: low nest survival, 
high predation rates, and small clutch size. Nests 
at our study site had a low survival rate, as only 
22.5 % of the nests produced at least one 
lledcling: predation was the major cause ot nest 
failure (67%). Nest predation was constant 
throughout the season and was not related to the 
time a nest was initiated. Nest mortality varied 
during the nestling cycle and was highest during 
the late nestling period (Fig. 2). Parental activity 
during this stage was highest around the nest 
