of secondary sexual characteristics that influence mate selection. Similar effects have been observed in other bird species. In medicine Parasite load has been shown to affect the spread of infectious diseases. For example, parasitologists at the Universidade de São Paulo researched the effect of Chaga's disease on the immune system. They found that individuals who survived the acute phase of infection develop parasite-specific immune response that reduces parasite levels in tissues and blood. This research aims to discover if the parasite load during the acute stage of infection affects if the host will eventually have a positive immune response. The research was conducted on mice, with the intention of eventually using the information gleaned from the experiments to assist humans who have contracted Chaga's disease. Marinho et al. found that parasite loads in the acute phase of infection correlates at the late chronic stage of the disease, with the intensity of the activation and response of the immune system of the host. This research could lead to new discoveries in parasitology. This could potentially prevent the spread of parasites and therefore diseases linked to parasite infection within a given population. Host stress Host stress causes conditions within the host to be less than ideal for parasites, leading to and causing parasite load. Malnutrition has been shown to suppress the immune system, leading to higher parasite loads within a population and increased transmission rates throughout the population. It has been shown that malnutrition, and putrefaction can lead to illness within a population and therefore increase the amount of parasites within a population. Those individuals that are malnourished and stressed exhibit the highest numbers of parasite load. This implies that these individuals have a higher likelihood of dying due to the environmental factors, as well as parasite infection, likely killing the population of parasites within that specific host. This would then limit the propagation of the parasites within the population. In the experiment conducted by Pulkkinen et al. it was found that when food was limited in a population of crabs infected with daphnia, there were mortalities among the infected population of crabs. This was due to stress within environment, as well as stress within the host (crab body) from parasite infection. Pulkkinen et al. also found that after a period of time there was a corresponding reduction in average size of crabs, and therefore the mortality rate due to malnutrition and