482 
THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 3. September 2011 
TABLE 1. Reproductive parameters of Mandarin Ducks during the 2004-2009 breeding 
Reserve, northeastern China. 
seasons in Zuojia Natural 
Variables 
Un-parasilized 
Parasitized 
Combined 
Number of nests with eggs 
24 
18 
42 
Number of nests with full clutch size 
21 
18 
39 
Number of nests successful 
16 
7 
23 
Number of nests that ducklings left 
16 
7 
23 
Clutch size (mean ± SD) 
9.7 ± 1.6 
18.8 ± 3.2 
14.0 ± 5.1 
Range, n 
7-12, 21 
15-25, 18 
7-25, 39 
Hatching rate in successful nests (%) 
88.7 ± 3.2 
83.5 ± 3.9 
87.1 ± 12.0 
Ducklings that left boxes (%') 
100.0 ± 0.0 
96.6 ± 1.7 
98.9 ± 2.8 
Number of ducklings left per nest 1 
t". 
o' 
+1 
-T 
oo 
15.4 ± 1.3 
10.5 ± 4.4 
a Only nests lhal ducklings left successfully were included. 
nest failure occurred during the brief period 
before young exited the nest box. The hatching 
rate for eggs in successful nests was 87.1 ± 
12.0% (n = 23), and rate of un-parasitized nests 
(n= 16) did not differ from that of parasitized (n - 
7) nests (t = 0.954, P = 0.351). Most (98.9%) 
ducklings left nests successfully. The average 
number of ducklings that left nests successfully 
for un-parasitized nests, parasitized nests, and 
combined was 8.4 ± 0.7 (/; = 16), 15.4 ± 1.3 
( n ~ 2), and 10.5 ± 4.4 (n = 23), respectively. 
Causes for Egg and Duckling Loss .—Nest 
desertion was the main cause for egg failures, 
accounting for 72.8%, followed by non-feniliza- 
tion (11.4%), and human disturbance (11.1 %); the 
remaining egg loss was due to embryo death and 
unknown reasons (Table 2). Five ducklings from 
three parasitized nests with large number of 
ducklings died before leaving the nest; we believe 
sibling trampling was the only cause of duckling 
loss before leaving nests. 
DISCUSSION 
Studies examining population-level frequencies 
of parasitically-laid eggs have reported brood 
parasitism increases with increasing nest densities 
in several species of waterfowl (Clawson et al. 
1979. Heusmann et al. 1980, Haramis and 
Thompson 1985, Eadie et al. 1998, Robertson 
1998, Waldeck et al. 2004). CBP occurred 
commonly among Mandarin Ducks in our study. 
CBP in this Mandarin Duck breeding population 
should not be due to a lack of nest resources 
because —43.6 ± 7.1% (n = 6) nest boxes were 
unused annually excluding boxes used by Man¬ 
darin Ducks and other birds in the study area. Our 
results are in agreement with the density hypoth¬ 
esis because frequency of CBP was positively 
correlated with number of boxes occupied by 
Mandarin Ducks. 
Native Mandarin Ducks in China breed later 
than the introduced population in Britain. Some 
introduced Mandarin Ducks have completed 
clutches in late March. However, native Mandarin 
Ducks in northeast China begin to lay in la 1 ' 1 
April, which is probably related to latitudinal 
geographic variation. Grice and Rogers (19651 
found CBP by Wood Ducks was more prevalent 
in early-season nests rather than late-season nesb- 
Davies and Baggott (1989a) reported similar 
Rel^heSr™ 2 g J°i S (° r 6e£? M ” darto ^ d “ i «« "« *»*• — 
Eggs unfertilized, % 
Embryos dead. % 
Nest desertion. % 
Nest tree deforested, 1 
Female dead, % 
Unknown reasons, % 
Un-parasitized nest" (n = 89) 
19.1 (9) h 
11.2 (3) h 
53.4 (6) b 
12.4 (l) b 
0 
2.2 (2) b 
° Three 
Numb; 
:n eggs were categorized as un-parasilized 
are the number of failed nests. 
Parasitized nests (n = 227) 
8.4 (6) b 
0.4 (l) b 
79.7 (10) b 
0 
10.6 (l) b 
0.9 (2) b 
Combined (n = 316) 
11.4 
3.5 
72.8 
3.5 
7.6 
1.2 
