Last year, Rob built and installed a bird house under our huge oak trees. Early this spring a Titmouse began singing for a mate in our front yard. His call was soon answered and we watched, as they built their nest in our bird house. After the nest was completed and a respectable amount of time had passed, I opened the door to the bird house and peeked in. There were 4 tiny eggs.
In time the eggs hatched and we observed the parents bringing fat green worms or caterpillars to their young. We peeked while the parents were away and saw the nest filled with four mouths opened wide. All we could see of the baby birds were their mouths. After a week or so the activity around the nest seemed to slow and I opened the door and saw a sleepy eye open - but the young birds didn't open their mouths. This is odd, I thought, but closed the door again to avoid causing stress to the parent birds.
Last weekend, the nest was quiet while we worked in the front yard, so I checked again and found all four baby birds had died. We removed the nest and took it and the baby birds to a local expert, the owner of The Bird Feeder (she has a degree in biology and has a wealth of information). She assured us that our opening the birdhouse wouldn't have driven the parents away and theorized that one of the parents might have died and the burden of feeding 4 babies was too great for the remaining parent. The babies must eat every 15 minutes. Another thought was that the parents might have fed poisoned worms to the young, but I assured her that we don't use pesticides in our yard so we doubt that was the cause. She also talked about how the bird count for Santa Cruz county is down this year and theorized that climate change is a cause. It's possible that the cycle of worms was out of sync with the cycle of the birds.
As we left the store, she said, "I'm sorry for your loss." I was surprised by her comforting words, but she was perceptive because I was feeling sad for the four youngsters who were so close to fledging before they died. Their wings were fully developed.
We are now fairly certain that something happened to the mother bird because the male has been appearing in our front yard and is advertising for a mate. We hope that when he is successful, he'll build a new nest in the same old birdhouse.