Thank you for your encouraging comment. Unfortunately, I don't know anything about the red spot's function.
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Thank you for your encouraging comment. Unfortunately, I don't know anything about the red spot's function.
I might have found the answer! It's appears to basically be a target that gull chicks can easily spot, so that they know where the food is. (Source)
Thank you so much for the investigation and your answer, @mightpossibly