The central tail feathers of the long-tailed finch (Poephila acuticauda) are a sexually dimorphic trait hypothesized to play a role in sexual selection. The longer tail feathers in males cost energy to produce, and this is thought to signal the male's excellent health condition. The table contains the lengths of the central tail feathers (average of the two central feathers, in millimeters) of 20 male and 21 female long-tailed finches.
Males: 87, 77, 95, 73, 74, 85, 56, 86, 95, 108, 75, 87, 73.5, 82, 89, 64, 74.5, 87, 85, 86
Females: 60, 59, 72, 54, 65, 58, 59, 65, 60, 68, 70.5, 80, 87, 65, 59, 65, 70, 66
How much longer, on average, are the central tail feathers of male long-tail finches compared to that of the females? A 95% confidence interval for the difference, Mf - Mm, in population mean length for the male and the female adult long-tail finches is lower bound to upper bound. (Enter your answers rounded to one decimal place)
Lower bound: 10.8
Upper bound: 22.5