Met at 8:30 at the reservoir. Both parents were feeding the chicks but not in the usual way, which has always been to fly directly to the nest, feed and fly off again immediately. Instead they would arrive with food (often Caddis Fly larvae) and land on an abutment, hop around, hop up the nearly-dry spillway, hop along the rim, and finally fly to the nest. Sometimes it was 5+ minutes before they delivered their food to the chicks. The explanation for this behavior was very likely attributable to the presence of a Great Blue Heron standing motionless on a limb in the pool below. It was paying no attention to the dippers and caught two fish as we watched. They were about 6” long, thin and reddish and were swallowed whole and alive. We left after an hour to go for coffee and I returned an hour later. The heron was gone and the feeding pattern had returned to close-to-normal. There was still some hesitation about going directly to the nest, but only seconds, not minutes.
I walked up the east side path to look at the nest. The opening is clearly visible and the chicks could be seen. I saw two cream-colored gapes when an adult arrived, and there may have been a 3rd. Fledging is still 10 days away.