Tail Feather Display of Carrion Crow

A pair of carrion crows (Corvus corone, family Corvidae) was spotted on the leafless treetop of a dawn redwood (Metasequoia glyptostroboides, family Cupressaceae). The one which perched on the higher branch flashed open and closed the tail feathers repeatedly just like a fan. But the crows didn't call at me. What does the behaviour mean? I wonder if it was a display of agitation or nervousness. Captured at dusk of early-February 2020 in Japan. For a full story (text in Japanese); https://sigma-nature-vlog.blogspot.com/2020/06/blog-post_27.html

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