brown wooden bird house on green grass during daytime

This bird house is on a tall post in my backyard. I had been watching the adult Bluebirds for months since they started 'courting'. The female laid four tiny blue eggs and I watched for the babies to appear and they did. After all those months of watching these birds I had to go into the city for the day. I came home and I had a feeling the bird house was empty. I was right. I had missed the fledglings fly away. :(