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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. Keywords: health state, leucocytes, nestlings, parasitism, pied flycatchers, recruitment.Résumé : Le nombre des différents types de leucocytes en circulation dans le sang peut fournir de l'information au sujet de l'état de santé des oiseaux dans la nature. Nous avons compté le nombre et déterminé les proportions de leucocytes circulant dans des frottis sanguins provenant d'oisillons gobemouches noirs (Ficedula hypoleuca) peu de temps avant leur premier envol. Nous avons de cette façon étudié la relation entre ces mesures hématologiques et des facteurs environmentaux, comme le parasitisme, la masse corporelle, la date de l'éclosion et la taille de la couvée. Le rapport entre les leucocytes neutrophiles et les lymphocytes est plus élevé chez les oisillons dont les nids sont infestés par des mites et chez les individus les plus légers, les leucocytes neutrophiles étant les cellules sanguines qui se manifestent le plus lors d'une malnutrition. Les oiseaux qui ont recruté dans la population avaient des numérations de lymphocytes et de leucocytes neutrophiles moins élevées au stade de jeunes au nid que ceux qui n'ont pas recruté. Ainsi, la numération des leucocytes neutrophiles serait un meilleur prédicteur du recrutement local que d'autres variables féquemment utilisées, comme la masse corporelle ou la date d'éclosion. En somme, nous appuyons l'hypothèse que les numérations de leucocytes neutrophiles constituent de bons indicateurs de santé chez les oisillons.

More colourful eggs induce a higher relative paternal investment in the pied flycatcher Ficedula hypoleuca : a cross-fostering experiment. Á J. Avian Biol. 37: 555 Á560.The signalling hypothesis of eggshell colouration in birds posits that females of species with blue-green eggs signal their phenotypic quality or the quality of their eggs to their mates through deposition of the antioxidant biliverdin as pigment. Males respond by investing more in the offspring. Through a cross-fostering experiment where we have exchanged whole clutches between pairs of pied flycatcher Ficedula hypoleuca nests, we managed to break potential associations between female quality and clutch chromaticity. We show that males respond to incubated clutches with more variable and higher peak values in blue-green chroma through a higher proportional investment in nestling provisioning on day 4 of the nestling period, when males invest more heavily than females in provisioning. More variable clutches show higher peak chroma values. We also show that egg colour during the two-week incubation period has a significant effect, which is not found for the colour of eggs during the laying period. Finally, the proportion of male provisioning visits affects negatively female brooding effort and nestling mortality, and thereby has positive effects on female fitness. Blue-green chroma in the pied flycatcher functions as a signal of female or clutch quality to males which respond by adjusting their relative investment with respect to total pair effort.

The evolution of different life-history strategies has been suggested as a major force constraining physiological mechanisms such as immunity. In some long-lived oviparous species, a prolonged persistence of maternal antibodies in offspring could thus be expected in order to protect them over their long growth period. Here, using an intergenerational vaccination design, we show that specific maternal antibodies can display an estimated half-life of 25 days post-hatching in the nestlings of a long-lived bird. This temporal persistence is much longer than previously known for birds and it suggests specific properties in the regulation of IgY immunoglobulin catabolism in such a species. We also show that maternal antibodies in the considered procellariiform species are functional as late as 20 days of age. Using a modelling approach, we highlight that the potential impact of such effects on population viability could be important, notably when using vaccination for conservation. These results have broad implications, from comparative immunology to evolutionary eco-epidemiology and conservation biology.

Compared to non-flying nest-dwelling ectoparasites, the biology of most species of flying ectoparasites and its potential impact on avian hosts is poorly known and rarely, if ever, reported. In this study we explore for the first time the factors that may affect biting midge (Diptera: Ceratopogonidae) and black fly (Diptera: Simuliidae) abundances in the nest cavity of a bird, the hole-nesting blue tit Cyanistes caeruleus, and report their effects on adults and nestlings during reproduction. The abundance of biting midges was positively associated with nest mass, parental provisioning effort and abundance of blowflies and black flies, while negatively associated with nestling condition. Furthermore, a medication treatment to reduce blood parasitaemias in adult birds revealed that biting midges were more abundant in nests of females whose blood parasitaemias were experimentally reduced. This finding would be in accordance with these insect vectors attacking preferentially uninfected or less infected hosts to increase their own survival. The abundance of black flies in the population was lower than that of biting midges and increased in nests with later hatching dates. No significant effect of black fly abundance on adult or nestling condition was detected. Blood-sucking flying insects may impose specific, particular selection pressures on their hosts and more research is needed to better understand these host-parasite associations.

Carotenoids are molecules that birds are not able to synthesize and therefore, must be acquired through their diet. These pigments, besides their function of giving birds red and yellow colouration when deposited in feathers, seem to act as immune-stimulators and antioxidants in the organism. Hence, only the healthiest individuals would be able to express carotenoid-based ornaments to a larger extent without compromising the physiological functions of carotenoids. Various studies have reported that birds infected by parasites are paler than those uninfected, but, to our knowledge, none of them has assessed the possible eVect of multiple infections by blood parasites on plumage colour. By comparing the yellow colour in the breast plumCommunicated by Heli Siitari. age of blue tits, Cyanistes caeruleus, between birds infected by diVerent numbers of blood parasite genera, we found that those birds infected by more than one genus were paler than those parasitized just by one. In addition, we examined the potential role of carotenoid-based plumage colour of blue tits as a long-term indicator of other parameters of health status, such as body condition and immunoglobulin and heat shock protein (HSP) levels. Our results indicate that more brightly coloured birds had lower HSP70 levels than paler birds, but we did not Wnd any signiWcant association between colour and body condition or immunoglobulin levels. In addition, we found a positive signiWcant association between Haemoproteus density of infection and HSP60 levels. Overall, these results support the role of carotenoid-based colours as indicators of health status in blue tits and show detrimental eVects of parasitism on this character.

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