Hagen et al. (2011) estimated the home range sizes of four bumblebees (Bombus) by fitting them with tiny radio transmitters and tracking their positions by plane and ground surveys. They estimated the mean home range size to be 20.7 ± 11.6 ha, where the number after the ± sign refers to standard error of the mean. 

a. Provide a description for the standard error. What does it measure?

b. What assumption are we making when calculating the standard error of the mean?

c. What would you recommend the researchers do next to reduce the standard error of their estimate of the mean home range size?