J Wildl Dis: Interspecific differences in hematozoan infection in Sonoran desert Aimophila sparrows.
Numerous studies have identified factors that control avian
hematozoan infections, but the mechanisms that account for host
differences in parasitemia remain largely speculative. To address this
issue, we compared the prevalence of these parasites in stained blood
smears from 4 conspecific Sonoran desert Aimophila sparrow species
sampled during their breeding season: rufous-winged (Aimophila carpalis;
RWSP), rufous-crowned (Aimophila ruficeps; RCSP), Cassin's
(Aimophila cassinii, CASP), and Botteri's (Aimophila botterii;
BOSP) sparrows. Blood smears contained Hemoproteus fringillae (RWSP),
Trypanosoma everetti (RWSP, RCSP, BOSP), Trypanosoma avium (CASP), and
microfilariae (all species). Most (92.5%) RWSP (n = 40) were infected
with Hemoproteus, but this parasite was not detected in RCSP (n = 20) or
BOSP (n = 20) and was found only in one (2.5%) CASP (n = 40).
Trypanosoma sp and microfilariae were detected in all species, but
prevalence differed between these 4 sparrow species. Species differences
in parasite prevalence were not due to difference in sex, age, adult
body mass, incubation period, breeding habitat, or plumage colorfulness.
However, differences in Hemoproteus sp prevalence correlated with
preferred nesting height, as RWSP generally nest above ground, whereas
the other species nest on or close to the ground. Elevated H fringillae
prevalence in breeding-condition RWSP presumably does not result from a
seasonal relapse associated with breeding or require new infection
because this prevalence did not differ in males sampled during and
outside (n = 21) the breeding season, and all male RWSP (n = 25) that we
held in captivity and shielded from new infections and influence of
natural photoperiod for 1 year had viable blood H fringillae
gametocytes. H fringillae prevalence in fall-sampled hatch-year male
RWSP (n = 11) was 63.6%, demonstrating that this parasite can be
transmitted on the breeding grounds and during the first months of life.
T everetti prevalence in RWSP was lower in winter than in summer and
also in long-term captive than in free-ranging adults. Presence of this
parasite in the blood of breeding males may depend on recrudescence of
existing infections or new infections.