Use the godwit data in Practice Problem 5 to test whether the mean arrival dates of male and female partners differ significantly. What assumptions are required?

Data from problem 5 

Birds of many species retain the same breeding partner year after year. In some of these species, male and female partners migrate separately and spend the winter in different places, often thousands of kilometers apart. Yet they manage to find one another again each spring. In a field study of individually banded pairs of black-tailed godwits, Gunnarsson et al. (2004) recorded spring arrival dates of males and females on the breeding grounds in the year after they were observed breeding together. The data for 10 pairs are provided in the accompanying table. Arrival date is measured as the number of days since March 31.