Malaria is caused by a microscopic blood parasite that is transmitted in the bite of female mosquitoes, which need a blood meal to produce their eggs.

Pregnant female mice were housed next to males infected with Babesia microti, which is a mild blood parasite causing few symptoms, but some anaemia.

By assessing the colouration and state of health of 195 free-living urban pigeons, they found that darker pigeons had lower concentrations of a blood parasite called haemosporidian.