Disease Affects Females Breeding Potentials

Abstract from Functional Ecology
15th April 1996

A study by K. Allander and Gordon Bennett (Functional Ecology, 9: 677-682), addresses a widespread problem which has hardly been studied at all - what is the role of disease in the lives of birds?

It is obviously impossible to ask the Great Tits whether they are feeling under the weather! So blood samples were taken to find out whether the birds were parasitised by the same sorts of organisms that cause malaria in man. No fewer than 84% had parasites and older birds were more likely to be infected but had a lower load than first year ones. Parasite-free females both started laying earlier (3.2 days) and hatched earlier (2.7 days) than infected birds. The effects of parasites in the males were not significant.

It is suggested that competition by the parasites within the female reduces the energy needed for egg formation - much greater than the energy needed for sperm formation. These effects on the females will significantly reduce the productivity of infected birds.

Chris Mead