Some functions are expected to return a single int (the first two) while others are expected to return a slice (the third). The tests align with what the functions ought to return: the first two tests expect an int and the third wants a slice. Are you seeing something different?
// TotalBirdCount return the total bird count by summing
// the individual day’s counts.
// BirdsInWeek returns the total bird count by summing
// only the items belonging to the given week.
// FixBirdCountLog returns the bird counts after correcting
// the bird counts for alternate days.