Great tits sing at a higher frequency in noise polluted urban surroundings than quieter ones to help overcome the auditory masking that would otherwise impair other birds hearing their song. Although great tits achieve a change in song frequency by switching song types, in other urban birds the change in frequency might be related to the<unk> . For instance, in humans, the<unk>  results in speakers adjusting frequency The<unk>  or<unk>  reflex is the involuntary tendency of speakers to increase their vocal effort when speaking in loud noise to enhance the audibility of their voice. This change includes not only loudness but also other acoustic features such as pitch, rate, and duration of syllables. This compensation effect maintains the auditory signal-to-noise ratio of the speaker's spoken words. The effect links to the needs of effective communication, as there is a reduced effect when words are repeated or lists are read where communication intelligibility is not important. Since the effect is involuntary it is used as a means to detect malingering in those simulating hearing loss. Research on birds and monkeys find that the effect also occurs in the vocalizations of animals. The effect was discovered in 1909 by Étienne<unk> , a French otolaryngologist.
Lombard effect
Widowhood effect
Ceiling effect 
Bystander effect 
Martha Mitchell effect
Whitten effect
Bouba/kiki effect
Weekend effect