Deep-diving beaked whales dive together but forage apart

Abstract

Echolocating animals that forage in social groups can potentially benefit from eavesdropping on other group members, cooperative foraging or social defence, but may also face problems of acoustic interference and intra-group competition for prey. Here, we investigate these potential trade-offs of sociality for extreme deep-diving Blainville′s and Cuvier's beaked whales. These species perform highly synchronous group dives as a presumed predator-avoidance behaviour, but the benefits and costs of this on foraging have not been investigated. We show that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. This enables whales to coordinate their mean travel direction despite differing individual headings as they pursue prey on a minute-by-minute basis. While beaked whales coordinate their echolocation-based foraging periods tightly, individual click and buzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.

Adult male Cuvier's beaked whales (Ziphius cavirostris) engage in prolonged bouts of synchronous diving

“…This conclusion is further supported by recent observations we have made over multiple resightings of synchronous animals instrumented with telemetry tags and confirmed to be in the same surface groups visually (unpublished data). Finally, evidence from another population of this species has shown similar group synchrony including during shallow dives observed in animals instrumented with higher resolution telemetry tags (Aguilar de Soto et al, 2020;Alcázar-Treviño et al, 2021).…”

“…Synchrony may be beneficial in cooperative foraging (e.g., Benoit‐Bird & Au, 2009; Parks et al, 2014). There is some evidence, however, that Cuvier's beaked whales that surface in groups may separate while foraging at depth, before rejoining during ascent (Aguilar de Soto et al 2020; Alcázar‐Treviño et al, 2021; see also sperm whales; Watkins et al, 1985; Irvine et al, 2017). Even if animals do not coordinate prey‐capture attempts, maintenance of synchrony in diving pattern may be beneficial if individuals use eavesdropping to find areas of high prey availability (e.g., Barclay, 1982; Gannon et al, 2005; Götz et al, 2006).…”

Trade-offs in telemetry tag programming for deep-diving cetaceans: data longevity, resolution, and continuity

“…We also compared depths from two different tag types deployed on different individuals in the same group in 2019, as animals in the same group at the surface are known to maintain high levels of synchrony [14, 15, 16, 17]. One of these tags was identical in type and programming to our 2018 time-series only satellite tags; the other was a shorter-term bio-logger attached by suction cups (DTAG) archiving pressure at 250 Hz, processed and decimated to 25 Hz [18].…”

Acoustic‐based estimates of Cuvier's beaked whale (Ziphius cavirostris) density and abundance along the U.S. West Coast from drifting hydrophone recorders

“…Ideally, group size for acoustic estimates of abundance and density would be determined acoustically. Although beaked whales remain close enough during foraging to eavesdrop on their group members, they forage independently (Alcázar-Treviño et al, 2021). This separation between members of a group provides a potential mechanism for estimating group size acoustically.…”