Red-winged blackbird males defend territories and attract females to mate and raise young there. A male protects nests and females on his territory both from other males and from predators. Males also frequently mate with females on adjacent territories.

When males are successful in mating with females outside their territory, do they also attempt to protect these females and their nests from predators? An experiment measured the aggressiveness of males toward stuffed magpies placed on the territories adjacent to the males (Gray 1997). This aggressiveness was measured on a scale where larger scores were more aggressive and lower scores were less aggressive. This aggressiveness score was normally distributed. Later the researchers used DNA techniques on chicks in nests to identify whether the male had mated with the female on the neighboring territory. They compared the aggressiveness scores of the males who had mated with the adjacent female to those who had not. The results are as follows:

Test whether there are differences in the mean aggressiveness scores between the two groups of males. Are males aggressive to a different degree depending on whether they had mated with a neighboring female?

Transcribed Image Text:

Mean aggressive-ness score Mated with neighbor Mated with neighbor Did not mate with neighbor Did not mate with neighbor -0.168-0.168 0.8060.806 Standard deviation of aggressiveness score 1.1351.135 0.5430.543 Sample size (n) (n) 10 10 36 36