Today's "post" in Edwin Way Teale's A Walk Through the Year speaks of how humans long ago based their plans on natural events that would vary some each strict (and later invented) calendar year. He says the Iroquois felt the best time to plant corn is "when oak leaves [have] become as large as a mouse's ear," and the Greek poet Hesiod remarked that summer arrives when the thistle blooms.
This wonderful naturalist Dr. Teale, married to another wonderful naturalist, speaks of how even now we may feel say "autumn has arrived" not on the autumnal equinox necessarily but when, in the Teales' case, a flock of evening grosbeak birds alights in the grounds of their lovely farm, or "winter has come" with the first snowstorm...
the Teales' autumnal bird, from a google search:
