22.09.2019 – Efficient scrounging
Scrounging or stealing food from other creatures is an expected phenomenon in the ocean if you consider the difficulty in getting something proper to eat and the opportunistic behaviour of most marine animals. In some cases, feeding situations are a harmonious social experience, a symbiosis, where several species may even work together during a hunt and share the prize. In other cases the scrounger simply steals the food from those that worked for and earned it.
The two species of cetaceans we encountered during todays trips, the Bottlenose dolphins (Tursiops truncatus) and Short-finned pilot whales (Globicephala macrorhynchus), are often encountered together, although today they were both seen separately. According to recent observations it is assumed that the altruistic Bottlenose are more likely to initiate the interaction and they may do so for several reasons. One of them may be to gain advantages in hunting deep-sea squid, an area of expertise for the pilot whales. To encounter such a mixed group is always exciting but both species are just as delightful when encountered separately. The Bottlenose dolphins charmed the guests aboard our afternoon trip on the Stenella with their undeniable charisma and incredible curiosity.
During almost every sighting, birds are involved, with the Cory’s Shearwater (Calonectris borealis) and Yellow-legged gulls (Larus michahellis) being the most frequently encountered species. When cetaceans hunt they often trap fish just beneath the waters surface giving the birds an easier time in snatching some of the prey. However, if a Great Skua (Stecorarius skua) happens to be close by things can get a little tricky for other marine birds. These large, brown-coloured birds of prey usually pass over the archipelago’s waters in late summer or autumn and come here to harass other marine birds for their food, a behaviour known as kleptoparasitism. Kleptoparasites steal food from other animals rather than getting it themselves. Skuas have even been observed injuring or killing young shearwaters, making the nervosity of marine birds when these large predators are looming nearby quite understandable. We observed such anxiety amongst the juvenile Yellow-legged gulls we saw feeding this afternoon, as the Skua entered the flock from afar, flashing the white markings under its wings as it swooped down to scrounge the prey from the young birds. Thankfully for the gulls, the Skua was largely outnumbered and quickly left the scene after scoring one fish but the short spectacle was incredible to witness!
By Paula Thake
Sightings of the day
10:00 Short-finned pilot whales
15:30 Bottlenose dolphins