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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1, March 2011 
TABLE 1. Parasite prevalence (percentage of nests parasitized), parasite intensity (mean number of larvae/nestling and 
per nest), latency of parasitism (time elapsed since hatching of the first nestling and nest parasitism), and date first brood of 
Red-crested Cardinals was parasitized for three breeding seasons (2005-2008) in central Argentina woodlands. 
2005-2006 
2006-2007 
2007-2008 
Parasite prevalence 
8/36 (22.2%) 
12/45 (26.7%) 
17/50 (34%) 
Parasite intensity 
14.4 ± 1.6 
10.8 ± 1.8 
13.4 ± 1.7 
(x ± SE of larvae/nest) 
(range: 9-22) 
(range: 3-26) 
(range: 3-29) 
Parasite intensity 
6.7 ± 1.3 
6.5 ± 1.4 
6.4 + 0.9 
(x ± SE of larvae/nestling) 
(range: 4.5-16) 
(range: 2.5-19) 
(range: 1.7-16) 
Latency of parasitism 
3.0 ± 0.38 
3.3 ± 0.35 
3.2 + 0.39 
(x ± SE of age of nestlings) 
(range: 2-5) 
(range: 2-6) 
(range: 1-6) 
Date first brood parasitized 
10 Jan 
31 Dec 
11 Jan 
variables. We used Fisher’s exact or Chi-square 
tests for the analysis of contingency tables. 
Reported values are means itSE. All tests were 
two-tailed and differences were considered sig¬ 
nificant at P < 0.05. Statistical tests were 
completed using STATISTICA 7.0 (StatSoft Inc 
2004). 
RESULTS 
Prevalence and Intensity of Parasitism during 
the Breeding Season.—The prevalence of botfly 
parasitism was 28.2% (37/131 nests) and did not 
differ between years (X 2 2 = 0.85, P = 0.65; 
Table 1). There was a positive association be¬ 
tween occurrence of botfly parasitism and time of 
breeding for the three breeding seasons (logistic 
regressions: 2005-2006, X 2 x = 14.2, P < 0.001; 
2006-2007, X 2 ] = 17.1, P < 0.001 and 2007- 
2008, Y 2 , = 36.1, P < 0.001) with most 
parasitized nests (36/37) occurring in January 
and February (Fig. 1). We divided the breeding 
season into 15-day intervals and calculated the 
proportion of nests that were parasitized with 
botflies for each interval to examine if the 
seasonal increase in parasite prevalence during 
January and February was associated with a 
decrease in availability of nests. We combined 
the data for the 3 years because of the small 
number of periods per year. There was no 
significant association between number of nests 
with nestlings and botfly prevalence (Spearman’s 
rank correlation: p = -0.20, P = 0.52, n = 12; 
Fig. 1). All nestlings were parasitized in 35 of 37 
nests. Botfly intensity was 6.5 ± 0.66 larvae/ 
nestling (range: 1.6-19, n = 37 nests; Fig. 2A) 
and was not statistically different between years 
(Kruskal-Wallis test: H 2 = 0.12, P = 0.93; 
Table 1). Mean parasite intensity per nestling 
did not differ between nests with one, two or three 
nestlings (Kruskal-Wallis test: H 2 = 3.4, P = 
0.18, /2 = 37) and was not associated with date of 
hatching (Spearman’s rank correlation: p = 0.1, P 
= 0.55, n = 37). Latency of parasitism (time 
elapsed since hatching of the first nestling and 
nest parasitism) was 4.2 ± 0.2 days (range 2- 
6 days, n = 35 nests; Fig. 2B) and did not differ 
across years (Kruskal-Wallis test; H 2 = 0.6, P = 
0.74; Table 1). 
Lethal and Sub-lethal Eff ects of Botfly Parasit¬ 
ism. —Thirteen of 37 nests parasitized by botflies 
were depredated and excluded from analysis of 
nestling survival. No nestlings fledged in 4/24 
nests (17%), there was partial fledging (some 
nestlings fledged, some died) in 7/24 nests (29%), 
and all nestlings fledged in 13/24 nests (54%). 
Nestling survival was lower in parasitized than in 
non-parasitized nests (parasitized: 0.6 ± 0.07, n = 
FIG. 1. Botfly parasitism of Red-crested Cardinals at 
different times of the breeding season in Buenos Aires 
Province, Argentina. White circles show the number of 
nests that produced nestlings during the 15-day interval and 
black circles = the percentage of those nests parasitized by 
botflies. Data correspond to the breeding seasons of 2005- 
2006, 2006—2007. and 2007—2008 combined (n = 
131 nests). 
