You are welcome. Nature is not sympathetic or very patient with old age or disabilities. In fact, nature is very cruel in this sense so most old and injured animals do not make it in the wild. It is the old "survival of the fittest" explanation. To protect the gene pool, decrease predators in a habitat area, and open new habitats for younger and healthier animals or promote nesting/mating habitats for mating pairs, nature promotes the removal of anything that can affect the above. Not having a mate and an established nesting/mating habitat along with the protection of a mate and offspring can also cause Carl to yield to the other birds. Good question. The Regal Swan