Getting Goosed in Autumn

Our calendars denote changes in months and seasons, but often we mark the passing of time with significant and obvious changes in the world outside. Here in the Skagit Valley, autumn begins when the snow geese and trumpeter swans arrive. The last week in October the first wedges of swans passed over my house. Shortly afterwards the snow geese arrived. We have yet to get the heavy rains that often begin by early November and continue through December. But, the swans and geese have arrived, and it clearly feels like fall now. Of course sunset at 4:30 enforces the autumn mood as well.  Throughout the world, it's different-some events change abruptly-others subtly. But a date on a calendar is only how we mark the passage of time in our world of commerce, commitment, and order. In the natural world, it's not always so clear or timely. What natural events do you associate with welcoming a seasonal change?