8.
Crossbills and food An ecologist studying breeding
habits of a bird called the common crossbill in dif-
ferent years finds that there is a linear relationship
between the number of breeding pairs of crossbills
and the abundance of spruce cones. In the table,
statistics are given for 8 years of measurements,
where x = average number of cones per tree and
y = number of breeding pairs of crossbills in a
certain forest.50
x = average number
of cones/tree
y = number of
crossbill pairs
Mean
23.0
18.0
Standard
deviation
16.2
15.1