Chickadee mimics snake hiss and movement to scare off feared predator

Chestnut-backed chickadee makes sudden hissing sounds and movements when a larger bird lands on top of the nesting box. She fans out her tail feathers over her young and simultaneously jumps up against the box and makes the loud hissing sound. This happened on the San Francisco south bay peninsula at 8:06 PM on May 27, 2021.
This behavior is described in "Behavioral Mimicry in the Titmice and Certain Other Birds" by Charles G. Sibley:
"... the survival value of the 'snake display' is obvious. The occurrence of such a display in hole-nesting species is certainly correlated with the fact that there is but one avenue of entrance and exit. The incubating bird cannot escape from a predator capable of entering the nest opening. A high survival value is thus imposed upon any mechanism capable of inducing escape reactions in the intruder. The proof of the effectiveness of an explosive hiss, with or without an accompanying sudden movement, is found in the fact that this same pattern has evolved independently in hole-nesting birds of widely different origins ..."
"The suggestion was advanced above that the 'snake display' constitutes an example of behavioral Batesian mimicry [a benign species mimics the appearance of a dangerous one]. It may well be argued that an explosive hiss is of itself a startling sound and that mimicry is not necessarily involved. This viewpoint would hold that the occurrence of hissing in snakes and in hole-nesting birds is simply a matter of convergent evolution. The case for mimicry is based on the fact that many snakes are actually dangerous to possible predators on the birds and thus the harmless mimic derives an advantage by its resemblance to the harmful model."
"The effectiveness of the hissing sound in frightening mammalian predators is to be found in their demonstrated sensitivity to sibilants. Rayleigh showed that the sound sss has most of its energy in the band between 8 and 12 kilocycles per second, to which the human ear is relatively insensitive. This same band of frequencies includes the peak of sensitivity for the rat (Rattus) . The hiss of a snake is undoubtedly far louder and more frightening to a rat than it is to a man."
Behavioral Mimicry in the Titmice (Paridae) and Certain Other Birds" by Charles G. Sibley , Wilson Bulletin, Volume: 67, April-June 1955
sora.unm.edu/n...

[@lannyhsu708]

lol looks like a curious California towhee i think

[@graychang99]

Yes, I agree it's a California towhee. In my yard, I also see dark-eyed juncos, mourning doves, Bewick's wrens, and hummingbirds.

[@womantisful]

Do you clean out the nestbox of last year's nest in preparation for spring?

[@graychang99]

Yes