1. Echolocation is the ability of some animals to orient themselves through sound emission and interpretation of the echoes. This is bats' main sense for orientation and recognising biotopes that provide food, water, and roosts. It is widely accepted that echolocation call frequency is related to body mass, and this relationship has been described as the 'allometric hypothesis', which proposes a negative correlation between these variables. 2. There is evidence that, in many cases, the allometric hypothesis does not apply. Additionally, studies supporting this hypothesis were done at the family level, resulting in a broad range of correlation values with r ranging from −0.36 to −0.76, and only insectivorous bats were included. Due to the notable exceptions and the lack of a quantitative synthesis of this hypothesis including all echolocating bats, we evaluated the allometric hypothesis of echolocation calls for this group. 3. Using a meta-analysis and phylogenetic generalised least-squares techniques, we evaluated the relationship between echolocation call peak frequency and the body mass of bats. 4. We found a negative relationship between body mass and echolocation call peak frequency for the 85 bat species that were included in our analysis (r = −0.3, p = 0.005). The relationship was consistent when we analysed the data at the insectivorous guild level, and in bats belonging to the families Vespertilionidae, Rhinolophidae, Emballonuridae, and the genus Myotis. However, the wide range of r values suggests that the strength of the relationship between peak frequency and body mass varies within the order Chiroptera. 5. Our results support the allometric hypothesis of sound production in echolocating bats. However, the low coefficient we found suggests that factors other than body mass may influence the peak frequency of echolocation calls produced by bats.

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