Deng et al. • CONSPECIFIC BROOD PARASITISM IN MANDARIN DUCKS 
483 
findings for Mandarin Ducks, as clutches in late 
March and early April exceeded 20 eggs; 
however, in late May clutches consisted of 10 
eggs or less. We found two obvious laying peaks 
in the Mandarin Duck population studied, and 
most CBP occurred in nests initiated early in the 
breeding season (Fig. 1). This supports the 
hypothesis that females may adopt a mixed 
reproductive strategy of combining early parasit¬ 
ism with late nesting (Trivers 1972, Lyon and 
Eadie 2008). 
Un-parasitized nests took longer to complete 
than anticipated with a laying rate of one egg per 
day. while parasitized nests took a shorter time 
than expected. We estimated that 2.5 females laid 
eggs in the same box based on eggs appearing per 
day. which was similar to the findings of Davies 
and Baggott (1989a). Mandarin Ducks laid on 
consecutive days or at longer intervals ranging 
from l to 6 days. Thus, it is possible that a female 
laying parasitically at one nest site was responsi¬ 
ble for the break in laying at another, as has been 
demonstrated for marked individuals of Wood 
Ducks (Clawson et al. 1979). 
Consistent with reports of others (Campbell and 
Ferguson-Lees 1972, Cramp 1977, Lever 1977), 
clutch size for un-parasitized nests of Mandarin 
Ducks ranged from seven to 12 eggs in our study. 
The recorded maximum clutch size for the species 
in a single box was 36 eggs (Davies and Baggott 
1989a), while the maximum clutch size was 25 
eggs in our study. This variability may be 
associated with the number of females that laid 
eggs in the same box. 
The hatching rate for eggs in all successful 
nests of Mandarin Ducks was 87.1 % in our study, 
which was higher than the 70% reported for the 
species by Davies and Baggott (1989b). and also 
higher than ~60% for Wood Ducks (Davis 1978, 
Zipko 1979, Moore 1981, Haramis and Thompson 
1985, Semel et al. 1988). Lower hatching success 
of Wood Ducks was frequently associated with 
factors caused by CBP including nest desertion 
and inefficient incubation, which may ultimately 
influence the reproductive success at the popula¬ 
tion level (Semel et al. 1988). Our results indicate 
'he parasitic behavior in the Mandarin Duck 
breeding population studied has not reached the 
problematic levels reported for Wood Duck 
populations. 
Ten parasitized and six un-parasitized nests 
received no subsequent incubation due to nest 
desertion in our study, which has also been 
reported for nest parasitism of Wood Duck nests 
(Jones and Leopold 1967, Haramis and Thompson 
1985, Semel et al. 1988. Roy et al. 2009). Several 
other factors may also affect desertion frequency 
of parasitized nests, including disturbance of 
laying or incubating females by parasitic females 
(Davis 1978, Semel and Sherman 1986) and the 
large number of eggs laid (Moore 1981, Semel 
and Sherman 1986). Nest desertion can also occur 
in response to factors unrelated to parasitism, 
including nest predation (Hill and Sealy 1994, 
Hosoi and Rothstein 2000). human disturbance 
(Rothstein 1975). broken or leaking eggs (Scott 
and Lemon 1996), and nest-site competition 
(Semel and Sherman 2001). Nest predation and 
broken or leaking eggs were not observed in our 
study, and the high rate of desertion might relate 
to nest parasitism. However, factors other than 
parasitism including disturbance from repeated 
nest inspection by researchers and interspecies 
competition for nest sites can not be excluded. 
Further study is required to identify factors 
responsible for nest desertion in this breeding 
Mandarin Duck population. 
ACKNOWLEDGMENTS 
We thank Jing La. Y. H. Pan, J. W. Zhang, X. H. Wang, 
and Hui Wu for assistance with collecting data in the field. 
We also thank an anonymous reviewer from Efdanz Writing 
for helping us to refine the manuscript into idiomatic 
English. R. A. Kennamer and an anonymous referee 
provided helpful suggestions for improvement of the 
manuscript. Financial support was provided hy the National 
Natural Science Foundation of China (No. 30970375), 
Training Fund of Northeast Normal University’s Scientific 
Innovation Project (No. 07013). and Jilin Provincial 
Science and Technology Department (No. 20070558). 
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