After a repeat trip to the site it was surmised that the Treehunter photographs taken at Los Bajos del Volcán could well be of two parent birds, even though only a single bird was visible at any one time. Here is a shot of what is perhaps the nest site, with one of the parent birds carrying what seems to be an insect pupa:

As is the case with many (if not most) furnariids, male and female Treerhunters cannot be distinguished in the field, while it is also supposed that both sexes also share duties in feeding the young. The next image shows what looks like a captured tree frog, presumably the next offering to the nestlings.

John relates that food was served, never visibly devoured, with a frequency of return of about 10 minutes within a timespan of 1 hour. This was recorded in two sessions of about half an hour each, and perhaps not all deliveries were seen. Congratulations to John on his patience and skill with a species that is not easy to observe and whose behaviour has rarely been photographed so well.