On June 11, 1998, Dennis Wiley, the park manager at Champoeg State Heritage Area, saw a kestrel (which had a nest near by) fly up to the front of a nest box, hang from the hole and reach its head into the nest box. When the box was checked the tree swallow nestlings were still in the nest. The nest was 1" below the hole. Apparently, the kestrel could not reach the nestlings.

On June 12, 1998, Dennis Wiley checked a nest box and found 3 bluebird eggs. This was the beginning of a second clutch for the pair and the female had built a second nest on top of a swallow nest, placing the top of the nest about 1" below the hole.  The next day, when the nest was checked, the eggs were gone and there was dried yolk dripped down the front of the box.  The nest was not otherwise disturbed. This nest box was on a post covered with greased sheet metal, and there was no evidence of a predator (raccoon or snake) climbing up the post. The kestrel was very likely the culprit. Other nests on greased metal poles have lost eggs and nestlings to apparent avian predators.