Variation in the whistle characteristics of short-beaked common dolphins, Delphinus delphis, at two locations around the British Isles

Abstract

The vocal repertoire of many delphinid odontocetes includes narrowband tonal whistles used mainly for communication. The aim of this study was to describe the whistle repertoire of short-beaked common dolphins, Delphinus delphis, recorded in the Celtic Sea between May and August 2005. The 1835 whistles recorded were classified into six broad categories and 30 sub-types, of which simple upsweeps and downsweeps were the most common. Furthermore, the parameters duration, inflections, steps and various frequency variables were measured. The whistles covered a frequency span from 3.56 kHz to 23.51 kHz and had durations between 0.05 and 2.02 seconds. Whistle parameters varied with behavioural context, group size and between encounters. The whistle repertoire of Celtic Sea common dolphins was compared to that of D. delphis from the Western Approaches of the English Channel, recorded during a survey between January and March 2004. The relative abundances of the broad whistle types did not differ between the two locations, but most whistle parameters were significantly different: almost all frequency variables measured were significantly higher in English Channel whistles. This may indicate some degree of population structuring of short-beaked common dolphins around Britain. Alternatively, the common dolphins in the English Channel may have shifted the frequencies of their vocalizations up to avoid masking by low-frequency ambient noise produced by high levels of vessel traffic in this area.

Review of Underwater and In-Air Sounds Emitted by Australian and Antarctic Marine Mammals

“…Instead, this species' vocalisations have been described from New Zealand [149,150], the Eastern Tropical Pacific [151,152], the UK [153][154][155], the Mediterranean [156][157][158] and the Atlantic Ocean [158]. Whistles have fundamentals from 3 to 24 kHz and last 0.01-4 s [149][150][151][152][153][154][155][156][157][158][159]. Burst-pulse sounds have been reported at 2-14 kHz, lasting 0.5-0.75 s [157]; however, recordings from Australia appear much more broadband with energy up to 160 kHz (Fig.…”

Whistle characteristics and daytime dive behavior in pantropical spotted dolphins (Stenella attenuata) in Hawai‘i measured using digital acoustic recording tags (DTAGs)

“…For example, whistle frequency parameters differ among populations of short-beaked common dolphins (Delphinus delphis; Ansmann et al, 2007), Indo-Pacific bottlenose dolphins (Tursiops aduncus; Hawkins, 2010), and common bottlenose dolphins (Tursiops truncatus; May-Collado and Wartzok, 2008). Furthermore, spectral and temporal whistle characteristics and vocal behavior are known to be influenced by factors such as group size, whistle type, behavior, stress and ambient noise levels (Morisaka et al, 2005;Ansmann et al, 2007;May-Collado and Wartzok, 2008;Rankin et al, 2008;Esch et al, 2009;Hawkins, 2010), which all may vary across time and space. Around the main Hawaiian Islands, three insular populations of pantropical spotted dolphins have recently been designated: an O'ahu stock, a 4-Island stock and a Hawai'i Island stock (Caretta et al, 2014).…”

“…A combined assessment of whistle characteristics from pantropical spotted dolphins in the ETP and in Hawai'i found minimum and maximum frequencies of 8.4 and 18.0 kHz, respectively (Oswald et al, 2007). However, because whistles from these populations were combined, the extent to which these parameters may vary among populations is not known; geographic variation in whistle characteristics has been documented in other delphinid species and could exist for pantropical spotted dolphins (e.g., Morisaka et al, 2005;Ansmann et al, 2007;May-Collado and Wartzok, 2008;Hawkins, 2010).…”

Macro- and micro-geographic variation of short-beaked common dolphin’s whistles in the Mediterranean Sea and Atlantic Ocean

“…Finally, ambient noise level also plays a role in the whistle structure of dolphins (MORISAKA et al 2005b;MAY-COLLADO & WARTZOK 2008). Man-made noise has been suggested as the explanation for acoustic differences described both in the frequency and modulation of short-beaked common dolphins' (Delphinus delphis) whistles between the English Channel and the Celtic Sea (ANSMANN 2005;ANSMANN et al 2007). Intra-specific variation in this type of vocalization has been assessed both at macro-(differences that occur over long distances and between populations that are geographically separated (KREBS & KROODSMA 1980)) and micro-geographic scales (variation between contiguous groups; KREBS & KROODSMA 1980), especially for Tursiops spp.…”