Habitat-dependent breeding biology of the Blue Tit(Cyanistes caeruleus)across a continuous and heterogeneous Mediterranean woodland

Mediterranean woodland environments are characterised by high spatial and temporal heterogeneity,which means the inhabiting species face a wide variety of selective pressures.Species may respond differently to habitat heterogeneity and so distinct eco-evolutionary scenarios may be responsible for the inter-habitat variability in reproductive strategies observed in certain species.The inter-forest variability of some reproductive traits in passerines has been examined by comparing forest patches or separated fragments.However,there is still little information regarding how such highly mobile animals adjust their breeding performance across continuous and heterogeneous woodlands.Here we studied the reproductive performance of a population of Blue Tits(Cyanistes caeruleus) in an area of continuous Mediterranean woodland that included two mountain slopes and four different types of forest,ranging from deciduous oak forests to perennial non-oak forests.We studied the habitat heterogeneity and inter-forest phenotypic variation in terms of reproductive performance and adult and nestling biometry,besides also exploring the effects of ectoparasites on Blue Tit reproduction.Eggs were laid earliest in deciduous Pyrenean Oak(Quercus pyrenaica) forests,while clutch size and the number of fledglings were highest in the humid Pyrenean Oak forest,which had the greatest tree coverage and most humid climate,and lowest in the coniferous Scots Pine(Pinus sylvestris) forest.There were no inter-forest differences in hatching(percentage of nests with at least one egg hatched) and fledging(percentage of nests in which at least one nestling fledged)success.Similarly,there were no inter-forest differences in adult and nestling biometry,but adults that raised more fledglings had a lower body mass,while males whose females laid larger clutches had smaller tarsi.Most ectoparasites did not affect Blue Tit reproduction,although Culicoides had a negative impact on nestling body mass.These results suggest that Blue Tits can adjust their reproductive effort to the forest where they breed even across a very small spatial scale.Different eco-evolutionary scenarios,such as phenotypic plasticity or genetic structuring and local adaptation,might explain the phenotypic differentiation in the reproductive strategies observed over small areas in woodlands.

Within-brood body size and immunological differences in Blue Tit(Cyanistes caeruleus)nestlings relative to ectoparasitism

Several ectoparasites parasitise nestlings decreasing their body condition,growth and survival.To minimise any loss of fitness due to ectoparasites,birds have developed a wide variety of defence mechanisms,potentially including hatching asynchrony.According to the Tasty Chick Hypothesis(TCH),the cost of parasitism would be reduced if ectoparasites tend to eat on less immunocompetent nestlings,typically the last-hatched chick in asynchronously hatched broods,as they are in poor body condition.Two predictions of the TCH are that immune capacity is lower in smaller nestlings than in larger ones and that parasites should provoke a more negative effect on smaller nestlings.Here,we test these predictions in a population of Blue Tits(Cyanistes caeruleus)whose broods are parasitised by Hen Fleas(Ceratophyllus gallinae)and Blowflies(Protocalliphora azurea).We recorded the presence of both ectoparasites and analysed the immunocompetence(number of leucocytes per 10,000 erythrocytes and cutaneous immune response to phytohaemagglutinin)and body condition of smaller and larger nestlings within individual broods.The leucocyte count was higher in smaller nestlings than in larger ones,whereas the cutaneous immune response did not differ between smaller and larger nestlings.Smaller nestlings,but not larger nestlings,had lower body mass when fleas were present.Blowflies,by contrast,had no detectable negative effect on nestlings.Overall,our findings provide partial support to the TCH.Lower immune capacity in smaller nestlings than in larger ones was not supported,but Hen Fleas seemed to negatively impact on smaller nestlings more than on larger ones.