Associations of Forest Type, Parasitism and Body Condition of Two European Passerines, Fringilla coelebs and Sylvia atricapilla

Abstract

Human-induced forest modification can alter parasite-host interactions and might change the persistence of host populations. We captured individuals of two widespread European passerines (Fringilla coelebs and Sylvia atricapilla) in southwestern Germany to disentangle the associations of forest types and parasitism by haemosporidian parasites on the body condition of birds. We compared parasite prevalence and parasite intensity, fluctuating asymmetries, leukocyte numbers, and the heterophil to lymphocyte ratio (H/L-ratio) among individuals from beech, mixed-deciduous and spruce forest stands. Based on the biology of bird species, we expected to find fewer infected individuals in beech or mixed-deciduous than in spruce forest stands. We found the highest parasite prevalence and intensity in beech forests for F. coelebs. Although, we found the highest prevalence in spruce forests for S. atricapilla, the highest intensity was detected in beech forests, partially supporting our hypothesis. Other body condition or health status metrics, such as the heterophil to lymphocyte ratio (H/L-ratio), revealed only slight differences between bird populations inhabiting the three different forest types, with the highest values in spruce for F. coelebs and in mixed-deciduous forests for S. atricapilla. A comparison of parasitized versus non-parasitized individuals suggests that parasite infection increased the immune response of a bird, which was detectable as high H/L-ratio. Higher infections with blood parasites for S. atricapilla in spruce forest indicate that this forest type might be a less suitable habitat than beech and mixed-deciduous forests, whereas beech forests seem to be a suboptimal habitat regarding parasitism for F. coelebs.

Effects of forest structure on the interaction between avian hosts, dipteran vectors and haemosporidian parasites

“…Contrary to our predictions, we did not find an effect of female vector abundance on haemosporidian parasitological parameters in any of our avian host species. We hypothesized that forest structure should indirectly affect parasite infection risk because of its known effects on vector abundance [16,19]. Variation of parasite prevalence in birds has been observed as within-year seasonal variation, reflected by the seasonal variation of vector abundance, distribution or exposure [29].…”

“…atricapilla there was significantly higher prevalence in spruce dominated forest stands than in mixed and beech forests [ 16 , 19 ]. Such differences were interpreted as a result of increased intra-specific competition for suitable habitat (i.e., beech forest for F. coelebs ), or as living in suboptimal habitats (i.e., S. atricapilla in spruce forests); in both cases there was a negative impact of forest structure parameters on body condition and immune status, increasing parasite infection risk [ 16 , 19 ]. In our study, we analyzed host-vector-parasite interactions within beech forests only; beech forest age classes did not per se represent the intricate structural differences as a result of management, as for example spruce forest does.…”

“…The effects on fitness are reflected in body growth and condition [15], and also in the birds' ability to invest in immune responses to fight-off pathogens (e.g. [16]). Outcomes of this trade-off can be observed in bilateral asymmetries, such as that of tarsus growth, which reflect early developmental challenges that depend on available resources of the place the young birds inhabit [17].…”

Avian haemosporidian parasites in an urban forest and their relationship to bird size and abundance

“…Heterogeneities of the environment also play an important role in infection risk; such as closeness to water bodies where vectors are more abundant (e.g. Wood et al 2007;Knowles et al 2014), and different forestry practices that can create puddles for vector breeding, which increases infection probabilities (Lüdtke et al 2013). Although we found a significant interaction between body size and abundance, it seems that there is not a strong trade-off between these two variables in regard to infection probability.…”

Spatial and seasonal variation of avian malaria infections in five different land use types within a Neotropical montane forest matrix

“…When hosts are located in sub-optimal conditions, there are higher costs when infection occurs because there is a trade-off between using limited resources to combat the infection or to do body maintenance and compete for territories (e.g. Lüdtke et al, 2013). Hence, we expected an increase in parasitaemia and a decrease in aggregation in the coffee plantation and urban forest, where habitat characteristics (i.e.…”