It is believed that animals living in northern regions have shorter appendages than animals living in southern regions. Random samples of birds were selected from each group and wing lengths for birds (in millimeters) were measured. The following table gives summary statistics.

Region	n	Average	Standard deviation
Northern (N)	33	113.0	1.2
Southern (S)	33	114.0	2.5
Difference (d = N - S)	33	-1.0	1.1

(a) Find an 80% confidence interval for the mean difference of wing lengths of birds between the northern regions and the southern regions. (Round your answers to 4 decimal places, if needed.)