If some of the birds are darker than the others.
return birds ;return #1 that are darker ;return number of  #1 ;return number of  #2 ;return difference of #3 and #4 ;return if  #4 is at least one ;return if  #5 is at least one ;return if  both  #6 and #7 are true
['select', 'filter', 'aggregate', 'aggregate', 'arithmetic', 'boolean', 'boolean', 'boolean']