No, the two species will not interbreed. Some juvenile birds will pal around with other species, especially if they are being chased by their own kind to compete for nesting and food habitats. We would think that this is probably the case. Both of these birds may have been outcasts and decided to hang around each other because neither was a threat. However, once they reach breeding age and the hormones start erupting, their behavior toward each other could significantly change once a mate of their own species appears. The Regal Swan