Answer: The correct answer is- to see what new traits might appear next.
As per the information in the question, pigeon breeder selects the offspring of pigeons with spotted bodies.
Spotted body is a trait that would be depicted by two different alleles ( such as one for black and other for white color).
As both the alleles for the color are represented in the pigeon offspring, therefore, it is a case of co-dominance ( let us take its genotype as Bb, where 'B' is allele for black and 'b' for white color).
When pigeons with spotted bodies are cross bred, they can produce pigeon with spotted and non spotted ( such as black 'BB', white 'bb', or spotted 'Bb' ) body depending upon the allele that is passed to the offspring.
Thus, pigeon breeder selects the spotted bodies pigeons and then breed those offspring to see what new traits might appear next.