HEARING IN THE RED-BILLED FIREFINCH LAGON O S TIC TA SENEGALA AND THE SPANISH TIMBRADO CANARY SERINUS CANARIA: THE INFLUENCE OF NATURAL AND ARTIFICIAL SELECTION ON AUDITORY ABILITIES AND VOCAL STRUCTURE

ABSTRACT

We tested the auditory sensitivity of red-billed firefinches Lagonosticta senegal0061 and Spanish timbrado canaries Serinus canaria. Both these species produce songs and calls that are narrowband and relatively high in frequency, with spectral energy falling predominantly in the region of 3–6 kHz. Hearing thresholds were measured in these two species and compared to the auditory sensitivity of closely related species: the well studied zebra finch Taeniopygia guttata, and other strains of canary bred for song. Auditory thresholds were similar in both groups of birds, with firefinches having an audiogram typical for that of small birds. Timbrado canaries exhibited an audiogram with its greatest sensitivity in the relatively high region of 4–6 kHz, corresponding to the peak frequency of its calls. Critical ratios measured over a range of several octaves increased in a monotonie fashion at a rate of 2–3 dB per octave for both firefinches and timbrado canaries. Critical ratios in these two species are similar to what has been found in most other small passerine species, suggesting spectral resolving abilities similar to most small birds tested to date.