First Sign of Spring?

In what could be the first preview of the upcoming spring, two birds that do not typically winter in the Colvin Run Habitat appeared in the last two days. First, an American Robin appeared and immediately visited the bird bath.
Unfortunately, the heater was out of the water, so the robin found only ice.
Second, a pair of Eastern Bluebirds appeared in the maple trees. The bluebirds did not visit the feeders. Blue birds have not been observed in the Habitat in the last five years. Their early arrival is a clear sign that I need to but out the bluebird house that I received as a Christmas present from my daughter and son-in-law.