Hornbill in the Mirror

Throughout the wet season last year at Mpala, we were lucky to have a mother red-billed hornbill (Tockus rufirostris) and her one fledgling frequently around the station. The little one imitated many of its mother’s behaviors, in particular the habit of landing on window sills and inspecting its reflection intently. On one occasion while in the library, I heard a repetitive loud tapping sound behind my head. I turned around to find the mom hornbill pecking at the window, turning her head from side to side to gaze at the reflected hornbill. The photo above is from that exact moment. I wonder if because she saw her reflection so often, she might think of her reflection as another hornbill individual that repeatedly greets her at windows and poses no threat (hornbills are territorial). I usually refrain from anthropomorphizing animals in my blog posts, but in this case I’ll entertain the idea of the mother hornbill teaching her offspring about the hornbill in the window. How puzzling it must have been for her to arrive the first time with her young and find that her “friend” has also appeared with a little hornbill!

One of the most fascinating behaviors that hornbills exhibit is involved in nest construction and maintenance. Before laying eggs, the female will collect moist substrate and compact it against the outer surface of a tree cavity, narrowing the entrance hole to the point where she can just squeeze in. From the inside she will continue to modify the hole, as does the male from the outside (in some hornbill species), entrapping the female inside the cavity. During incubation, the male will supplement the mother and chicks with food. When the female and growing chicks no longer fit inside cavity, the mother will break it open from the inside, only to patch it up again in front of the nestlings. Both parents will then continue provisioning their young and also for some time after they have finally fledged.

Cavity nesting is not uncommon in birds, but what is unusual is the female remaining in a space that she cannot exit. Supposedly this behavior is beneficial for offspring survival, providing protection for the eggs and nestlings specifically from predation by other hornbills. I was not lucky to witness nest construction in hornbills, so unfortunately I cannot provide a species-specific description of this remarkable behavior. Maybe next time! I should also note that this behavior is present in most hornbills but not all— some exceptions being ground hornbills in the genus Bucorvus.

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