Exercise 3 solution

January: 4 + 0 + 2 = 6
February: 5 + 1 + 0 = 6
March: 3 + 6 + 0 = 9
March had the highest total, 9. (Check: 6 + 6 + 9 = 21, matching the species totals 12 + 7 + 2.)

Why three months cannot show a trend (sample reasons): too few visits; weather and time of day vary from visit to visit; the same birds may be counted more than once; one place may not represent a wider area; a season's change may just be normal seasonal movement, not a long-term trend.