Santiago Merino

Are avian blood parasites pathogenic in the wild? A medication experiment in blue tits (Parus caeruleus )

The Hamilton and Zuk hypothesis on haemoparasite–mediated sexual selection and certain studies of reproductive costs are based on the assumption that avian blood parasite infections are detrimental to their hosts. However, there is no experimental evidence demonstrating harmful effects of blood parasites on fitness in wild populations, it even having been suggested that they may be non–pathogenic. Only an experimental manipulation of natural blood parasite loads may reveal their harmful effects. In this field experiment we reduced through medication the intensity of infection by Haemoproteus majoris and the prevalence of infection by Leucocytozoon majoris in blue tits (Parus caeruleus), and demonstrated detrimental effects of natural levels of infection by these common parasite species on host reproductive success and condition. The fact that some of the costs of infection were paid by offspring indicates that blood parasites reduce parental working capacity while feeding nestlings. Medicated females may be able to devote more resources to parental care through being released from the drain imposed upon them by parasites and/or through a reduced allocation to an immune response. Therefore, this work adds support to previous findings relating hosts life–history traits and haematozoan infections.

Mites and blowflies decrease growth and survival in nestling pied flycatchers

The effects of blood sucking mites (Acari) and blowfly larvae (Diptera) ectoparasites on the growth and survival of nestling pied flycatchers (Ficedula hypoleuca) breeding in nest boxes were studied. Mites significantly decreased mean within-brood tarsus length, a measure of skeletal size, and mass. High mite loads also increased within-brood variance in mass, although the effects varied depending on the quality of the nesting site. Significant interactions between the effects of mites and nest box quality and breeding phenology were detected, the lightest nestlings fledging from late, low quality nests with high mite loads. No effect of mite loads on nestling mortality was apparent. In contrast, blowfly larvae abundance contributed more to nestling mortality in one year, although this seemed to pave the way for brood survival in nests with high infestations. High abundances of both ectoparasite species were comparatively beneficial for pied flycatcher broods, suggesting a role for competition between ectoparasites that may ultimately increase host brood survival

The blood parasite Haemoproteus reduces survival in a wild bird: a medication experiment

While avian chronic haemoparasite infections induce reproductive costs, infection has not previously been shown to affect survival. Here, we experimentally reduced, through medication, the intensity of infection by Haemoproteus parasites in wild-breeding female blue tits Cyanistes caeruleus. However, this treatment did not reduce the intensity of infection in males or the intensity of infection by Leucocytozoon. Medicated females, but not males, showed increased local survival until the next breeding season compared with control birds. To our knowledge, this is the first empirical evidence showing long-term direct survival costs of chronic Haemoproteus infections in wild birds.

Haematological variables are good predictors of recruitment in nestling pied flycatchers (Ficedula hypoleuca)

ABSTRACT The number of different types of circulating leucocytes may provide information about the health state of birds in the wild. We counted the number and proportions of circulating leucocytes in blood smears of nestling pied flycatchers (Ficedula hypoleuca) shortly before fledging. We studied the relationship between these haematological measures and environmental factors like parasitism, body mass, hatching date, and brood size. The heterophils-to-lymphocytes ratio was higher in nestlings whose nests suffered from mite infestation and in lighter individuals, heterophils being the cells that responded preferentially to malnutrition. Recruited birds had lower lymphocyte and heterophil counts when nestlings than non-recruited ones. Our results show that heterophil count is a better predictor of local recruitment than other variables widely used for nestlings as survival predictors, like body mass or hatching date, supporting the hypothesis that low heterophil counts reflect a good individual health state in nestlings.

Sexual selection and tail streamers in the barn swallow

The functional significance of elongated, narrow tips of the tail feathers of certain birds, so–called tail streamers, has recently been discussed from an aerodynamic point of view, and the effects of sexual selection on such traits have been questioned. We review our long–term field studies using observational and experimental approaches to investigate natural and sexual selection in the barn swallow, Hirundo rustica, which has sexually size–dimorphic outermost tail feathers. Experimental manipulation of the length of the outermost tail feathers has demonstrated sexual selection advantages of tail elongation and disadvantages of tail shortening, with opposite effects for natural selection in terms of foraging efficiency, haematocrit and survival. These findings are contrary to the prediction of a general deterioration from both shortening and elongation, if the tail trait was determined solely by its effects on aerodynamic efficiency and flight manoeuvrability. Patterns of sexual selection in manipulated birds conform with patterns in unmanipulated birds, and selection differentials for different components of sexual selection in manipulated birds are strongly positively correlated with differentials in unmanipulated birds. Age and sex differences in tail length, and geographical patterns of sexual size dimorphism, are also consistent with sexual selection theory, but inconsistent with a purely natural selection advantage of long outermost tail feathers in male barn swallows.

Heterophil/lymphocyte ratios and heat-shock protein levels are related to growth in nestling birds

Abstract Growing altricial birds may experience nutritional stress in the nest due to sibling competition, food restriction, or parasites. Nutritional stress may be detected through its effect on nestling growth, although genetic and maternal effects may interfere with its expression. A more direct way of estimating nutritional stress may be through measurements of organismic stress in growing birds. Heterophil/lymphocyte ratios (H/L) have been proposed as reliable physiological indicators of the stress response. Heat-shock protein (HSP) synthesis is induced by animals in response to various stressors, making the concentration of HSPs a suitable measure of organismic stress. In a study of growing pied flycatchers (Ficedula hypoleuca), we assessed H/L from cell counts in blood smears and levels of two HSPs, HSP60 and HSP70, from the cell fraction of peripheral blood. H/L and the level of HSP60 were significantly positively associated in nestlings of 13 days of age, while the level of HSP70 was not related to the other two measures. Small nestlings with respect to tarsus length on day 7 had higher levels of HSP60 and higher H/L values. Brood means of nestling mass, tarsus length, and wing length shortly before fledging were negatively related to both mean HSP60 level and mean H/L ratio. Brood variances in body mass and wing length on day 13 were positively associated with mean HSP60 levels but not with mean H/L values. Up to 80% of variation in some traits was explained by stress indicators.

High Prevalence of Hematozoa in Nestlings of a Passefine Species, the Pied Flycatcher (Ficedula hypoleuca)

While this may be true in many passerines, mainly ground-nesting species with short fledgling periods, we show here that prevalences may be detected as early as 13 days of age in a cavity-nesting passerine. Prevalences and intensities of hematozoa in nestling birds may merit further study, as both parameters are relatively easy to quantify in smears of peripheral blood in bird species such as the Pied Flycatcher (Ficedula hypoleuca, Muscicapidae), which has a relatively extended fledgling period. In 1993, an intensively studied population of Pied Flycatchers in central Spain (Potti 1993) was sampled for presence of hematozoa. Adult birds were captured while incubating (females) or feeding nestling (males); a drop of blood was obtained from the brachial vein, smeared, air dried, and fixed with 100% ethanol. Slides were later stained with Giemsa for 45 min. In addi-

Daily energy expenditure and cell-mediated immunity in pied flycatchers while feeding nestlings: interaction with moult

Ecological immunology posits a trade-off between parental effort and immunocompetence underlying the cost of reproduction. The moult-breeding overlap observed in several bird species represents a conflict in resource allocation between two energy-demanding processes. Moult processes have been associated with enlargements of immune system organs. In the present study. we measured simultaneously daily energy expenditure (DEE) and the T-cell-dependent immune response of pied flycatchers, Ficedula hypoleuca, caring for grown nestlings. We used the doubly labelled water technique and the phytohaemagglutinin (PHA) injection assay on both males and females, while recording provisioning rates and moult scores. DEE and the PHA response were negatively correlated for females, but not for males. A significantly higher proportion of males than females initiated moult. Provisioning rates were strongly correlated with DEE for females but only for non-moulting males. The DEE of moulting males was marginally correlated with moult score. For moulting males, there was a marginally significant positive correlation between moult score and immune response. The trade-off between DEE and immunity for females could underlie the cost of reproduction. However, the moult-breeding overlap found in males may offset this trade-off, thereby reducing the implications of immunosuppression for parental survival.

BLOOD PARASITES OF PASSERINE BIRDS FROM CENTRAL SPAIN

Sixteen species of passerine birds captured during a 2.5 yr period in Central Spain were examined for hematozoa. Haemoproteus spp., Leucocytozoon spp., Trypanosoma spp., Plasmodium spp., and microfilariae were observed. The most prevalent species were in the genus Leucocytozoon. The majority of the records are new for Spain and some represent new host records. More than one-half of the birds examined were infected with at least one parasite species. These records are similar to those reported from other areas in northern Europe and the Iberian Peninsula.

Corticosterone metabolites in blue tit and pied flycatcher droppings : Effects of brood size, ectoparasites and temperature

The hypothalamic-pituitary-adrenal (HPA) axis of birds induces the secretion of corticosterone (CORT) as a response to different ecological variables. In this study we tested experimentally if manipulations of brood size or ectoparasitism led to subsequent differences in the concentration of excreted CORT metabolites of adult and nestling blue tits (Cyanistes caeruleus). No significant effect of the manipulation of brood size was detected in adults or nestlings. No significant effect of ectoparasitism was detected in males or nestlings, although females from uninfested nests showed lower concentrations of excreted CORT metabolites. In addition, we analysed if weather conditions had an influence on the concentration of excreted CORT metabolites of blue tits and pied flycatchers (Ficedula hypoleuca) breeding in the same forest. We detected no effect of weather conditions on adults, but nestlings of both species showed a negative correlation between their excreted CORT metabolites and the average mean temperatures they were subjected to during their growth. This effect was not found in blue tits in a colder year, suggesting that the sensitivity of the HPA axis to ambient temperature may be subjected to interannual variation. Moreover, we found a positive effect of the maximum temperature on the day of sampling on the concentration of CORT metabolites of blue tit nestlings in one of the years. These results suggest that weather conditions may act as environmental stressors to which the HPA axis of blue tit and pied flycatcher nestlings may be sensitive.