Experimental manipulation of cavity temperature produces differential effects on parasite abundances in blue tit nests at two different latitudes

was higher in males attending the heated nests in Germany, and the control nests in Spain. Moreover, both male body mass and nestling wing length were negatively related to the abundance of larval fleas. In conclusion, our results indicate that increased temperature at the nestling stage may affect the fitness of blue tits by altering parasite prevalence rates.