Aerial hearing thresholds and ecoacoustics of a threatened pursuit-diving seabird, the marbled murrelet Brachyramphus marmoratus

Abstract

As humans increasingly utilize sensitive coastal areas, diving seabirds like the marbled murrelet Brachyramphus marmoratus face a unique combination of exposure to pervasive anthropogenic sound and acoustically mediated disturbances in terrestrial and marine environments. Despite its threatened status, the sound sensitivities and sensory ecology of this species are unknown, limiting any predictions of the frequencies or sound levels that may induce acoustic impacts. In this study, we measured electrophysiological aerial hearing thresholds for 10 wild individuals captured, sedated, examined inside a field-deployed anechoic chamber and subsequently released. Auditory responses were detected across a 0.5 to 6 kHz frequency range. The median auditory threshold was lowest at 2 kHz (33 dB), while hearing was generally sensitive between 0.75 and 3.8 kHz. B. marmoratus thresholds were elevated compared to other studied alcid species. In-air sensitivities were used to provide an initial prediction of underwater hearing thresholds. To further explore the auditory sensory ecology of this solitary-nesting species, hearing data were also compared to short-term recordings (5 d) of the aerial soundscape of a marbled murrelet nesting habitat. The soundscape contained both abiotic and biotic sounds that contributed to broadband sound levels of 46-55 dB re: 20 µPa rms (0.2-10 kHz). This comparatively quiet habitat enabled relatively frequent detection of anthropogenic sounds within the soundscape. Energy from this acoustic pollution consistently overlapped marbled murrelet sound sensitivities, indicating that the species is susceptible to disturbance from a range of noise types.

Long distance calls: negligible information loss of seabird social vocalisations over propagation down to the hearing threshold

“…2020), down to 13 dB re 20 µPa in the 1-3.5 kHz range in the common murre ( Uria aalge ; Smith et al . 2023a), and down to 17 dB re 20 µPa in the 1-3.5 kHz range for the marbled murrelet ( Brachyramphus marmoratus ; Smith et al . 2023b).…”

“…across species, namely down to 10-20 dB re 20 µPa in the 1-2.5 kHz frequency range for the Atlantic puffin(Mooney et al 2020), down to 13 dB re 20 µPa in the 1-3.5 kHz range in the common murre (Uria aalge;Smith et al 2023a), and down to 17 dB re 20 µPa in the 1-3.5 kHz range for the marbled murrelet (Brachyramphus marmoratus;Smith et al 2023b). We chose 1000 m as the maximum propagation distance, with calculated ASPL at this distance roughly corresponding to the minimum physiological hearing threshold (i.e.…”