Seasonal and age‐related changes in blood parasite prevalence in dark‐eyed juncos (Junco hyemalis, Aves, Passeriformes)

Abstract

We determined seasonal changes in blood parasite infections in a free-living population of Dark-eyed Juncos (Junco hyemalis) breeding in interior Alaska (65 degrees N; 148 degrees W). The common parasites found in blood smears were Leucocytozoon fringillinarum (56%), Trypanosoma avium (33%), and Haemoproteus fringillae (9%). In males, parasite prevalences were relatively high at arrival on breeding grounds and increased during the breeding season. Intensity of infection with Leucocytozoon also increased between spring and summer, and then decreased at the time of migration (September). This decrease did not occur in adult females. Elevated prevalences during the breeding season probably reflected the addition of new cases via vector activity to positive status resulting from spring relapse. We observed neither an association between parasite species nor a consistent relationship between parasite intensity and body condition. To further study relationships between reproductive system activity and parasite infections, we compared prevalences in adult males that were undergoing their first cycle of gonadal development and regression (males in their second calendar year, or SY) with those of older males (males in their third or more calendar year, i.e., after-second-year males or ASY). Circulating testosterone concentrations declined in both groups between arrival on breeding grounds (end of April-early May) and the end of the reproductive period (July), and they were higher in May in ASY than in SY males. At the peak of the breeding season (June), ASY males also had a higher parasite prevalence than SY males. This difference may have resulted from immunosuppressive effects of gonadal hormones and/or from behavioral differences between SY and ASY males such that older males were exposed to more insect vectors than younger males. .

Occurrence of blood parasites and intensity of infection in Prunella modularis in the montane and subalpine zone in the Slovak Carpathians

“…The increase in prevalence with age could be explained by higher mortality of young birds (Valkiūnas 2005), deterioration in the immune function of adults (Cichoñ et al 2003), or increased exposure to the vectors (Ahmed and Mohammed 1978). Several authors have confirmed the relationship between host body weight and prevalence of blood parasites (Scheuerlein andRicklefs 2004, Marzal et al 2008), but this effect is not always present and similarly to our study, other past studies have reported no direct relationship between the occurrence of blood parasites and host body weight (Hauptmanová et al 2002, Deviche et al 2001, Palinauskas et al 2005. Clarification of this relationship is often complicated in wildlife field studies due to many uncontrolled variables (Madsen et al 2007).…”

“…Similarly to the results of Svobodová and Votýpka (1998), we have also recorded a higher infection intensity in adult birds than in subadults. Some studies have presented the opposite result for L. fringillinarum (Allander and Bennett 1994) or no significant relationship between haemoparasite prevalence and age of birds (Deviche et al 2001).…”

Determinants of prevalence and intensity of infection with malaria parasites in the Blue Tit

“…Similarly, a number of previous studies also reported an increase in prevalence with age (e.g. Weatherhead and Bennett 1991;Norris et al 1994;Seutin 1994;Deviche et al 2001). We did not find any effect of sex on infection status, when considering either pooled infections or infections with separate lineages (pTURDUS1, hPARUS1).…”

Hematological and parasitological health conditions of the Pale-breasted Thrush (Turdus leucomelas) (Passeriformes: Turdidae) in southeastern Brazil

“…If infection causes a decrease in health a decrease in all hematological parameters is to be expected in the breeding season. It has been postulated that seasonal variation in hemoparasite prevalence is related to intrinsic factors of the reproductive cycle (BENNETT et al 1982, DEVICHE et al 2001, GARVIN & GREINER 2003. This occurs because the greater effort and energy demands of the reproductive period conflicts with the energy necessary to maintain the or- ganism, compromising the immune system and individual health.…”