How Do You Know It's Spring?

Sure, the calendar says "March" and the first day of spring is less than a week away, but how can you tell if Spring is here to stay?

I know the snow has melted, but the forecast calls for more.

The crocus and tulips are poking out of the mud, but my roses still look dead.

The days are sometimes warm and sunny, but I can't be caught out at night without a coat.

The kids want to wear shorts and t-shirts to school, but come in freezing after playing.

But. . . .
The one true sign of Spring that has appeared many times at our house. . . . .

And I haven't seen a single one outside!