Answer: The estimated number of robins in the population is 550
Explanation: To estimate the population of robins, we will use the Mark-Recapture technique:
1) Capture a small number of individuals, mark them (with tags or other harmless identification) and release them;
2) After a period of time, catch another group and count the ones who have the mark;
3) Estimate the population using:

where
N is the estimate of individuals in the population
M number of individuals marked
C is the total number of individuals captured the second time
R is the number of individuals with the mark recaptured
For the population of robins:


N = 550
The best estimate for the robin population is 550.