The best-supported conclusion from the graph regarding the effects of fire ants on the birds is: C. The birds are less likely to survive when there are many fire ants, so the ants are likely taking over the niche of the birds.
What is the conclusion
The graph illustrates a negative correlation between the survival rate of birds and the percentage of bird nests treated with the ant-killing chemical.
As the percentage of treated nests (and thus, potentially fewer fire ants) increases, the survival rate of the birds also increases. This suggests that the presence of fire ants is negatively impacting the survival of the native bird species, indicating a potential displacement or adverse effect on the bird population due to the invasive fire ant species.