Le Gros et al. • URBANIZATION AND HOST-PARASITE INTERACTIONS 
789 
indicate that associations between parasites and 
their hosts can be either positively or negatively 
affected by urbanization. 
Tompkins et al. (2011). in their review of the 
effects of wildlife diseases on ecosystems, 
indicate a wider exploration of the effects of 
parasites on invasive species* success is needed. 
Further studies on the distribution and effects of 
parasites in relation to urbanization are needed as 
little is known about how urbanization affects 
parasites, and nest parasites in particular, and how 
these changes can affect urban bird communities. 
We investigated how the interaction between 
the Northern Mockingbird (Mimus polyglottos) 
and its nest parasite (Philomis porteri: Diptera: 
Muscidae) varies with urbanization. Previous 
research (Fokidis et al. 2008, Stracey and 
Robinson in press) demonstrated the mockingbird, 
an urban-positive species, increases in abundance 
with urbanization with peak densities occurring in 
residential neighborhoods (Stracey 2010). We 
considered the mockingbird a good model species 
test if the 'parasite-release* hypothesis might 
contribute to the success of urban-positive spe¬ 
cies. Dipteran nest parasites are known to have 
deleterious effects on nestlings and. at times, 
adults (Arendt 1985a, b; Hurtrez-Bousses et al. 
■W8; Simon et al. 2004; Segura and Reboreda 
^11), and assessing their presence is much less 
IDV asive than assessing blood parasites. Mocking¬ 
bird nests are more likely to be infected by this 
parasite than by fleas or mites (pers. obs.), and 
Philomis parasites are known to have negative 
l-iness consequences for nestlings, including 
b'ghcr mortality and decreased growth rates (Loyc 
^Carroll 1995, Dudanicc and Kleindorler 2006. 
Galligan and Kleindorfer 2009. Kleindorfcr and 
^udaniec 2009). Little is known, however, about 
hovv urbanization affects the abundance of P. 
imeri. We investigated how the distribution of P. 
I*>rieri changed with urbanization. We predicted. 
•*^don the ’parasite-release hypothesis', that we 
U(Jt| ld hnd fewer parasitized nests and lower 
'"tensities of parasitism (number of parasites per 
"ust; sensu Margolis el al. 1982) in urban habitats 
U| *h the lowest levels of parasitism in residential 
neighborhoods, where mockingbird density is 
highest. 
METHODS 
Study Species.— The Northern Mockingbird is 
an open-cup nesting, altricial bird that occurs 
[ hroughout the United States, southern Canada, 
Mexico, and the West Indies (Derrickson and 
Breitwiseh 1992). The breeding season in Florida 
starts as early as late February and ends in early 
August, and a pair can nest from one to five times 
during the breeding season (Derrickson and 
Breitwiseh 1992). Clutch size is between two 
and six eggs, and nestlings remain in the nest 
12 days with both parents providing care (Der¬ 
rickson and Breitwiseh 1992). 
Philomis porteri occurs in southern Texas and 
Florida (Dodge 1955, Kinsetla and Winegarner 
1974) and has been observed on at least three 
species of birds: Northern Mockingbirds. Eastern 
Bluebirds (Sialia sialis). and Great Crested 
Flycatchers (Myiarchus crinitus) (Kinsella and 
Winegarner 1974. Spalding et al. 2002). Larvae 
arc obligate subcutaneous parasites of nestlings 
and feed on blood, other body fluids, and cellular 
debris (Dudanicc and Kleindorfer 2006, Fessl et 
al. 2006). Adults are non-parasitic and may feed 
on decaying organic matter, fruits, or flowers 
(Dudanicc and Kleindorfer 2006, Fessl et al. 
2006). Philomis larvae are known to have 
negative Fitness consequences including reduced 
growth, diminished body condition, decreased 
fledgling success, and increased nestling mortality 
for at least some hosts (Arendt 2006, Dudaniec 
and Kleindorfer 2006. Dudaniec et al. 2007, 
Rabuffetti and Reboreda 2007. Huber 2008, 
Galligan and Kleindorfer 2009). Females of most 
species of Philomis lay eggs in the avian hosts’ 
nests. The larvae of subcutaneous species, after 
hatching, burrow under the nestlings' skin where 
they feed until they are ready to pupate. They then 
leave the nestlings, pupate in the nesting material, 
and emerge as adults 10 days later, allowing 
Philomis to produce several generations per year 
(Glasgow and Henson 1957. Kinsella and Wine¬ 
garner 1974, Uhazy mid Arendt 1986, Delannoy 
and Cruz 1991. 'Young 1993. Nores 1995, 
Spalding ct al. 2002. Arendt 2006, Dudaniec and 
Kleindorfer 2006, Fessl el al. 2006). The life 
cycles of many Philomis parasites have been 
partially described, but little is known about P. 
porteri. 
Study Sites —Our study was conducted at seven 
sites in and around Gainesville. Florida, USA 
during spring and summer 2007 and 2008. All 
study sites were within 50 km of Gainesville and 
were spread along an urbanization gradient. These 
sites were grouped into four types of habitat: 
wildlife preserve (1 site; Ordway-Swisher Bio¬ 
logical Station), pasture (2 sites), residential area 
