Once a common sight around London, house sparrow ( Passer domesticus ) populations have fallen for decades; They are down 71% since 1995. Now scientists believe they know why: A mosquito-borne disease called avian malaria.
Researchers gathered 3 years of data from 11 sparrow colonies around London where the birds grow. They counted raw numbers of birds each year and collected blood and annihilates from a number of individuals.
Seven of the 11 colonies lost birds, and about 74% of the mussels carried avian malaria ( Plasmodium relictum ). It is the highest rate of infection with this parasite seen in any wild bird population in Northern Europe, the researchers report today in Royal Society Open Science . Avian malaria can cause reductions in Western Europe, North America and India, too, says the team.
Like other forms of malaria, avian malaria spreads when mosquitoes bite birds and feed on their blood. The disease can lead to infections that can be fatal to the birds, and they can transmit the infection to their offspring. Most sparrows carry the parasite, but the number of parasites found in each bird's system was significantly higher in descending populations, especially in younger birds, the team found.
Scientists do not know why avian malaria is common in domestic mice, but they say that further research can provide clues.