Dove coos are known to be important for intra-specific communication in various contexts. Earlier research showed the occurrence of systematic frequency modulations for the perch-coo of the collared dove and suggested that presence or absence of these modulations might be important in communication. The present study examined the occurrence of frequency modulations and frequency use for perch-, bow- and nest-coo, as well as variation in these features between and within individuals, to assess the acoustic ‘signal space' for this species. The occurrence of frequency modulations was high for perch- and bow-coo, but low for the nest-coo. The relative distribution of modulations over the three elements of a coo differed for the various coo types. Coo types differed also in their ‘frequency profiles'. Frequency use is correlated with the occurrence of modulations. Differences between coo-types as well as variation within a coo-type and within individuals can be described by a limited set of parameters, which may be linked to basic properties of the coo producing mechanism. As a consequence of the occurrence of modulations and their distribution over the coo-types, the acoustic differences between the coo-types are amplified. As the different coo-types serve different functions, presence of modulations increases the signal space and decreases the ambiguity of the coo types. Differences between individuals exceeded those within individuals and were largest for perch- and bow-coo, which both serve in territorial defence and mate attraction.
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