The correct answer is B: Melting
Yes, over a period of time, and a few generations later, the birds would eventually adapt to the new situation. During Natural Selection, only the fittest that are best able to handle the change in environment will survive and pass on those traits that make them immune or resistant to the change, to their offspring.
Contemporary landscapes result from many causes, including variability in abiotic conditions, such as climate, topography, and soils; biotic interactions, such as competition, mutualism, herbivory, and predation, that can generate spatial pattern even when environmental conditions are homogenous; natural disturbances. I hope this helps :)