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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 1. March 2012 
exists regarding the effect of cowbird parasitism during the 
post-fledging period. We monitored 115 Ovenbird 
(Seiurux itumcupillit) nests in 2006-2008 in northcentral 
Minnesota, six of which were parasitized. We used 
radiotelcmctry to monitor movements of 36 Ovenbird 
fledglings (9 additional fledglings depredated <24 hrs 
after fledging were excluded from the movement analysis) 
from non-parasitized nests and one fledgling from a 
parasitized nest. Clutch sizes and produetiv ity were lower 
in parasitized Ovenbird nests than non-parasitized nests, 
similar to populations at other locations. The fledgling we 
tracked from a parasitized nest (in 2008) died after 2b days. 
It was the only fledgling in our study that died (n = 20) 
with no sign of predation and an empty stomach. That 
fledgling look 12 days to travel 50 m from its nest and 
25 days to travel >100 m from its nest. Fledglings from 
non-parasitized bruods tracked tor >25 days during 2008 
(n = 16) took4.1 ±0.71 anil 9.5 1 1.14 days to travel the 
same distances. Our observations suggest that negative 
effects of brood parasitism may persist into the post- 
fledging period, possibly confirming observations of 
cowbird-only survival compiled from the literature. 
Received 6 March 2011. Accepted 22 July 2011. 
Brood parasitism by Brown-headed Cowbirds 
(Molotlirus ater, hereafter cowbirds) has numerous 
negative effects on productivity of nesting migrant 
passerines (Rothstein 1990. Robinson et al. 1995, 
Ortega 1998, Lorenzana and Sealy 1999). Egg 
replacement by female cowbirds significantly 
decreases number of Ovenbirds ( Seitines auroca- 
pilla) fledged in parasitized nests (llann 1937. 
Donovan et al. 1995. Hersek et al. 2002). Cowbird 
parasitism significantly increased nest abandonment 
by California Gnatcatehers ( PolioptiUi califomicci) 
(Braden et al. 1997) and delayed nesting of Yellow 
Warblers {Seiophaga petechia) that bury parasitized 
clutches (Guigueno and Sealy 2010). Nest predation 
of parasitized songbirds is also influenced by the 
presence of cowbird nestlings. Predation of Amer¬ 
ican Redstart (S. ruticilla) nests was 16-19% higher 
in parasitized nests than in nests not parasitized by 
cowbirds (Hannon et al. 2009). Begging behavior in 
nestling songbirds is a significant factor contributing 
to nest predation (Haskell 1994) and cowbirds beg 
significantly more than nestlings of host species 
(Payne 1991). Experimental nests at which cowbird 
begging calls were broadcast were significantly 
more likely to be depredated than nests at which 
Indigo Bunting (Passerine) cyanea) calls were 
broadcast (Dearborn 1999). 
Substantial attention has been given lo effects of 
cowbirds on nesting success, but less is known about 
how cowbird nest parasitism impacts host broods 
during the post-fledging period. Smith (1981) 
monitored marked Song Sparrows ( Melospiza melo- 
dia) and found that fledglings experienced no 
significant reduction in survival due to brood 
parasitism. However, juvenile indigo Buntings from 
parasitized nests were 82% less likely to return to 
natal areas ii their second year than juveniles from 
non-parasitized nests (Payne and Payne 1997). 
Rasmussen and Sealy (2006) reported that adult 
hosts of parasitized broods, in 97 of 102 observations 
involving 42 species of hosts, were observed feeding 
cowbird fledglings, but not their own young. Airola 
(1986) found that parasitized family groups in the 
Sierra Nevada contained 76% fewer host fledglings 
than non-parasitized groups. These authors suggested 
the discrepancy in parental care may cause increased 
mortality ofhost fledglings in the early post-fledging 
period. The post-fledging period is a time of high 
mortality for many songbirds without additional 
stresses Iron cowbird parasitism (Ricklcfs 1968. 
King el al. 2006. Berkeley et al. 2(K)7). 
Cowbird fledgling activity occurs in four main 
phases: inactive, active, superactive. and indepen¬ 
dent (Woodward 1983). The inactive and active 
phases cover the first 11 days after leaving the 
nest when ihe cowbird develops the ability to fly. 
but generally does not actively beg or follow the 
host parent*. The superactive phase occurs 13 to 
23 days after fledglings leave the nest and is 
characterized by fledglings following host adults 
and near-ecnslant begging. The superactive period 
is followed by independence. 25 to 30 days after 
leaving the nest. Thus, cowbird-induced parental 
neglect of offspring may affect host fledgling 
survival up to 30 days into the post-fledging 
period. 
We slutied a population of Ovenbirds in 
northcentral Minnesota to assess the effects ol 
forest maragement practices on reproductive 
success. Ovenbirds generally do not remove 
cowbird eg«s or abandon nests at high frequencies 
in response to parasitism, but are capable of 
successfully raising cowbirds and their own young 
through the nesting period (Hann 1937. Hersek 
et al. 2002i. However, little is known about the 
effects of hood parasitism on Ovenbird fledgling 
survival. <Ve report an observation of one 
parasitized nest that supports the hypothesis that 
cowbird paasitism reduces host fledgling survival 
while the young are dependent on adult care. 
METHODS 
We searched for and monitored Ovenbird nests 
during the 2006-2008 breeding seasons in mature 
