The Wilson Journal of Ornithology 123(4):788-796, 2011 
ASSOCIATIONS BETWEEN NORTHERN MOCKINGBIRDS AND THE 
PARASITE PH1LORNIS PORTERI IN RELATION TO URBANIZATION 
AR1ANE LE GROS,'~ J CHRISTINE M. STRACEY.' 3 AND SCOTT K. ROBINSON 1 
ABSIRACT. We investigated associations between Northern Mockingbirds (Minins polyglottos) and the nest parasite 
Philomis ported (Diptera: Muscidae), and how they vary with urbanization in northccntral Florida. Our goal was to 
ascertain il the -parasite-release' hypothesis could contribute to high reproductive success of Northern Mockingbirds in 
urban areas. We collected 26 nests in 2007 and 73 in 2008 that had produced fledglings along an urbanization gradient, and 
measured the number of nests parasitized and the number of P. ported in the nests. Habitats differed in prevalence of 
Philomis parasitism, but not directly in relation to urbanization. Parking lots and wildlife preserves had low levels of 
parasitism, whereas residential neighborhoods and pastures had significantly higher parasitism prevalence. Parasite 
prevalence was also significantly and positively affected by nest height and percentage of ground covered by buildings, 
trees, and open areas in the study site. Our findings do not offer strong support for the 'parasite-release' hypothesis in 
relation to urbanization, but suggest that vulnerability to parasites is habitat-specific. Received 2 April 2010. Accepted27 
June 2011. 
Urbanization causes high local extinction rales 
and replacement of many species by others that 
survive well in urban areas (McKinney 2002, Blair 
2004, Gottscholk el al. 2007). which we refer to as 
urban-positive species (Slracey 2011). Numerous 
researchers (Adams 1994. Goring and Blair 1999. 
McKinney 2002. Chape and Walsh 2006. Shochut 
et al. 2006. Fokidis et al. 2008) have hypothesized 
that changes in predation and food resources arc 
responsible for the success of urban-positive 
species. Few siudies, however, have tested the 
hypothesis that urban-positive species are released 
from parasites that help regulate populations in 
native habitats. Urban species could be less 
exposed to parasites either because hosts are in 
better condition and have better immune systems to 
fight parasites (Fokidis et al. 2008) or because 
some parasites are less prevalent in urban areas 
(Marcogliese 2005). Some authors (Lafferty 1997. 
Marcogliese 2004, Sures 2004, Marcogliese 2005) 
suggest parasites are frequently the first species to 
be affected by ecosystem changes. 
Parasites have an important role in structuring 
many ecological communities (Minehella and 
Scott 1991). They can regulate host populations 
by increasing energetic demands, altering behav¬ 
ior, increasing mortality, reducing fecundity, 
altering nutritional status, reducing growth, mod- 
' Florida Museum of Nulural History, 305 Dickinson 
Hall, P. O. Box 117800, Gainesville. FL 32611. USA. 
"Current address: CRI, Universite Paris Descartes, 24 rue 
du Faubourg Saint Jacques, 75014 Paris, France. 
’Current address: Westminster College, 1840 South 1300 
East, Salt Lake City. UT 84J05. USA. 
4 Corresponding author; 
e-mail: ariane.le.gros@gmaiI.com 
itying interspecific competition, enhancing sus¬ 
ceptibility to predation, and altering mate choice 
and sex ratios (reviewed by Minehella and Scott 
1991). Loyc and Carroll (1995) reviewed the 
effects of ectoparasites on birds and found they 
affect nestling growth, body condition, and 
survival, as well as adult reproductive success 
and behavior. They concluded that blood-feeding, 
nest-dwelling parasites may significantly reduce 
host fitness. Tompkins et al. (2011) found that 
parasites frequently mediate the success of 
invasive species. If a similar mechanism is 
operating in urban habitats, an additional hypoth¬ 
esis for high abundance of urban-positive species 
may be decreased parasitism. 
Numerous recent studies measured the effects 
ol urbanization on host-parasite interactions along 
an urban gradient (Gregoire et al. 2002. Reperant 
et al. 2007. Fokidis et al. 2008. Geue and Partecke 
2008, Page et al. 2008. Evans et al. 2009. Lehrer 
et al. 2010). The frequency and the intensity of 
roundworm ( Bay lisa scans procyonis) infection in 
common raccoons (Procyon lotor). for example 
decreased with urbanization (Page et al. 2008 ) and 
the prevalence of some species of helminth 
parasites in red foxes (Vulpes vulpes ) also 
decreased with urbanization (Reperant et al 
2007) . Similarly, for songbirds, individuals in 
urban areas generally had fewer blood parasites 
(Fokidis et al. 2008), fewer Ixodes ticks (Gregoire 
et al. 2002. Evans et al. 2009). and lower risk of 
infection by blood parasites (Geue and Partecke 
2008) than in rural areas. Lehrer et al. ( 2010 ), 
however, found that prevalence of Toxoplasma 
gondii in woodchucks (Marmota monax) was 
positively related to urbanization. These studies 
788 
