Yes, if something scares the birds from an area or they do not like the habitat because of scarce food, shelter, etc., then they may look somewhere else. Are there predators in your area, i.e. domestic (dogs, cats, humans), or wild (alligators, foxes, coyotes, etc.)? If so, something could have happened to one or both of the swans or a close call and they left the area. There is also another possibility that has nothing to do with predators or the habitat and that is the weather. Animals and plants are very susceptible to quick fluctuations in temperature. With the weather we have been having lately, many animals and plants think that with the warmer temperatures, it is time to nest or bloom. However, a cold front appears and this activity may completely cease until the next front of warm weather. So, the swans may have gone to nest initially thinking that the winter was over only to be surprised that another cold front appeared. This could instantly cause their nesting behavior to cease. We hope this information is of benefit. The Regal Swan