Aristotle – the last human to know everything there was to know during his lifetime- was the first to write on subject of bird migration. He believed that small birds (particularly swallows) hibernated during the winter and this serve as conventional wisdom for almost 2000 years.
Aristotle also believed that birds morphed from one species to explain how one species would disappear near the end of summer (i.e. redstart) and another would appear to residence through the winter (i.e. robin). This process of change was called Transmutation.
It’s laughable now to think of “migration” in these terms but I believed I witnessed the latter the other day with my observation of the Trumpeter Swan. I went out the Portage the next day and saw 2 large dark-billed swans but they were clearly Tundras. Later in the evening I saw them from my liar .. I mean my lair, and this time the nearby Mute Swans did not respond to their presence and the Tundra’s were not observed in courtship display. I believe the Trumpeter’s transmutated into Tundra’s so that they could co-exist with the aggressive and territorial Mute Swans. I intend to watch to see if they turn back into Trumpeters but in the meantime I will transmute my yardlist to reflect the current form these swans have taken.