First Report of Epimeletic and Acoustic Behavior in Mediterranean Common Bottlenose Dolphins (Tursiops truncatus) Carrying Dead Calves

Abstract

Epimeletic behavior toward dead calves has been frequently reported in cetaceans, mostly with females (presumed mothers) showing supportive behaviors such as carrying, lifting, or sinking, often assisted by "escort" individuals. However, information on acoustic production in such contexts is scarce. This report describes two observations of epimeletic behavior toward dead newborns in bottlenose dolphins and associated acoustic production. Data were collected at the Tiber River estuary (Rome, Mediterranean Sea, Italy) with one hydrophone for passive acoustic monitoring and two digital cameras. In both cases, an individual (presumed mother) acting as the main supporter and directly interacting with the carcass by lifting it (case 1) or sinking it (case 2) was observed. Another adult individual (escort) was present in both encounters showing standing-by and excitement behaviors (case 1) and supportive behavior (case 2). In both encounters, whistles, pulsed sounds, and bray-call elements were recorded. The consistent vocal activity observed likely conveyed context-specific information. A signature whistle in the first encounter was also recorded, likely emitted by the putative mother as a distress call. This report confirms the occurrence of epimeletic behavior in bottlenose dolphins and reports a preliminary description of the acoustic production when a dead calf is involved, providing additional information on this largely unknown topic.

Keywords: Mediterranean Sea; Tiber River; Tursiops truncatus; acoustic behavior; bottlenose dolphins; dead calf; epimeletic behavior.

Figure 1

Map of the study site. The red rectangle represents the marine protected area “Secche di Tor Paterno” while the two diamonds represent the Single Point Moorings R1 and R2. The map also shows start and ending points (dots) and tracks (lines) of the first (blue) and the second (green) sighting.

Figure 2

Left picture: the dead new-born with visible fetal folds. Right picture: Edge of the new-born tail visibly marked.

Figure 3

The putative mother (“A”) carrying the dead calf on her rostrum.

Figure 4

The individual “B” (bottom dolphin) swimming close to the putative mother (upper dolphin).

Figure 5

Tail slap (left picture) and leaping close to the carcass (red circle) exhibited by the escort individual “B” (right picture).

Figure 6

Signature Whistle (SW_01) identified in the recordings from the first encounter (Hamming window, size 2048, DFT 2048, Overlap 50 %, Hop size 1024).

Figure 7

Carcass of the calf with the fetal folds still visible and inflated belly.

Figure 8

UNIRM_142 passing over the carcass (left picture), pushing it up with the rostrum (middle picture) and carrying it on the dorsal fin (right picture).

Figure 9

Left picture: UNIRM_025 passing over the carcass; right picture: UNIRM_025 (right dolphin) swimming close to UNIRM_142 (left dolphin). Red circles highlight the carcass.