A researcher discovers two populations of birds that are similar. The two populations live in habitats that are different. What evidence might suggest to the researcher that the birds belong to different species rather than the same species?

A: Some birds appear to be hybrids of the birds in the two populations. 
B: The birds in the two populations have different mating behaviors. 
C: Birds in the two populations sometimes feed in different locations.  
D: The two populations of birds feed at different times of the day.