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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 4. December 2011 
(residential) and low (pastures) host densities. We 
did not consider other hosts of P. porteri, which 
might affect host-spccific parasitism rates (Ost- 
feld and Keesing 2000). Kleindorfer and Duda- 
niec (2009), for example, found that parasite 
intensity was significantly higher for nests with 
many close heterospecific neighbors in a related 
species of botfly. P. porteri has been documented 
in nests of two other species: Eastern Bluebirds 
(Spalding et al. 2002) and Great Crested 
Flycatchers (Kinsella and Winegarner 1974. 
Spalding et al. 2002), both of which occurred in 
wildlife preserves, pastures, and residential areas, 
but were uncommon in parking lots (CMS, 
unpubl. data). We do not have data on parasitism 
rates of these species, nor do we know if 
additional species also serve as hosts. 
It is unclear if urbanization affects the distri¬ 
bution of P. porteri. This parasite may benefit 
from changes caused by moderate levels of 
human land modification, such as in pastures 
and residential areas. Residential areas in Gaines¬ 
ville still contain native vegetation and arc 
characterized by moderate percentages of ground 
covered by buildings (7.06 and 28.49% at our 
study sites) and pavement (5.80 and 19.44% at 
our study sites. Table 3). This pattern has also 
been documented for the Brown-headed Cowbird 
(Molothrus ater ), a brood parasite, which reaches 
highest abundance at moderate levels of urbani¬ 
zation (Chace et al. 2003), although undoubtedly 
for different reasons. Our findings offer weak 
support, al best, that the ’parasite-release* hy¬ 
pothesis could explain why urban-positive species 
like mockingbirds are so successful in urban 
areas. Only the most extreme urban environments 
appear to offer a refuge from botflies and birds 
nesting in habitat with the most natural vegetation 
also had a refuge from high levels of botfly 
parasitism. Our results arc difficult to interpret 
without a more complete understanding of the 
ecological factors that affect the distribution of P. 
porteri. The importance of P. porteri selective 
pressure on mockingbirds relative to both other 
parasites and other factors (i.e., food and 
predators) is unknown. Our study highlights the 
limitations in our understanding of how urbani¬ 
zation affects bird communities through its 
effects on parasites. Given the potential of 
parasites to have an important ecological role in 
structuring bird communities, continued research 
into the affects of urbanization on parasites is 
vital. 
ACKNOWLEDGMENTS 
We thank G. J. Sleek for identifying (he parasite Judil 
Ungvari-Martin for assistance with nest dissection, and 
Steve Daniels. T. J. Richard, and R. E. Hanauer for help 
with Held work. We thank Butler Plaza, the Oaks Mall, the 
University of Florida Beef Research Units. Ordway- 
Swishcr Biological Station, and all homeowners who 
granted permission to work on their properties. 
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