I have been hearing this sweet bird for over a year now and thought I was hearing an owl. Only about a week ago I was enjoying sitting out in the sun on my deck and heard the sweet sound. I looked around and amazingly enough I spotted him in my very large maple tree. He was very kind and stayed long enough for me to photograph him. When I would hear him throughout the day I would wonder how an owl could be making so much noise during daylight hours. Now in case you think I'm odd for thinking this bird was an owl when I asked a friend if they knew what bird could be making the sound they too thought it was an owl. I believe this is a Mourning dove. In case your interested in hearing their sound you can go to the link I pasted below.
http://www.allaboutbirds.org/guide/Mourning_Dove/lifehistory
Ramon en het paard van Sinterklaas (2015)
9 years ago