10.01.2019 – Dynamic duo

The Atlantic gave us a warm welcome on placid waters this morning with large groups of our dynamic duo here in Madeira; Short-finned pilot whales (Globicephala macrorhynchus) and Bottlenose dolphins (Tursiops truncatus). This combination of species has been extremely frequent these past months and we had two sightings involving both of them today.

It’s always fascinating to watch two species of cetaceans socialize with one another but we can’t help ask ourselves if such aggregations are random or if there are specific reasons for such interspecific interactions. If so, which of the two species is more likely to initiate such associations. Our colleagues in La Gomera on the Canary Islands asked themselves the same questions and discussed several hypotheses as to why these animals frequently travel in each others company while taking into account the observations they themselves made during whale-watching trips.

The team concluded that such groupings are more likely to be initiated by Bottlenose dolphins. This theory resulted from observations that are partially similar to those made by our team here in Madeira. Sightings of these associations are often made in deep waters, the preferred habitat of pilot whales. The pilot whale herds within these interspecific groups are also usually much larger than the number of acompanying Bottlenose dolphins although the species tend to have a similar average number of individuals within a travelling herd.

As opportunists, Bottlenose dolphins may actively seek out groups of pilot whales for foraging success, social reasons or as a protection from predators. Pilot whales like to hunt in deep waters for squid, a valuable prey that is also occasionally pursued by other delphinids due to its high water and fat content. Pilot whale herds may therefore indicate the presence of squid for the Bottlenose dolphins and perhaps they even hunt side by side. The large, bulky pilot whales may also help protect the Bottlenose dolphins from potential predators that may endanger sick or juvenile members of their school, like several pelagic shark species.

Social reasons may also be behind such remarkable aggregations. Although Bottlenose dolphins are notoriously altruistic, the curiosity and will to interact seems to be mutual amongst the members of both species. What’s worth mentioning, is that the interactions we observed in the last years between these two toothed whales seem very peaceful. Who knows, maybe some of the animals have even established interspecific friendships with one another and occasionally meet in Macaronesian waters? Wouldn’t that be something…

By Paula Thake

Sightings of the day

Stenella

10:00 Bottlenose dolphins, Short-finned pilot whales