A look at the huge appetites of whales

AS EVERY whale-watcher knows, a feeding frenzy of noisy seabirds out on the open ocean usually means there’s a whale underneath. Whalers, long ago, hadn’t the fancy technology sailors and fishermen have today; they often relied on birds to guide them to their quarry.

Mon, 21 Dec, 2015 - 00:00

Richard Collins

Gulls and gannets converge on hunting whales to feed on ‘the scraps which fall from the rich man’s table’. The huge mammals are an indirect source of food for birds but are there dangers in working with them? Do whales even eat seabirds?

Conor Ryan, Padraig Whooley, Colin Barnes and Simon Berrow of the Irish Whale and Dolphin Group (IWDG) raise these questions in the current edition of Irish Birds.

On December 3, 2008, while taking biopsy samples and identification photos of whales 11km south of Glandore, Co Cork, the IWDG team found three dead gulls floating within a few metres of each other. Two of the victims were kittiwakes, dainty ocean-going gulls which only come ashore to breed. The third was a herring gull, the familiar scavenger of a town dumps and follower of ships.

Twelve fin, five Minke and four humpback whales where feeding in the area. Eight days later, 25 dead seabirds were found close to where 12 fin and five humpbacks were plunge-diving. The death list this time included herring gulls, kittiwakes, gannets, guillemots and razorbills.

The birds were freshly dead; one herring gull carcass was still warm when taken from the sea. The IWDG team believe that all were killed by whales. Had they been ‘run over’ by these huge trucks of the sea, sucked under and drowned? Were they ‘ingested and regurgitated’ by the lunging giants, the authors ask?

That most of the victims were juveniles supports these suggestions; young inexperienced birds may not be streetwise enough to keep out of trouble. Remains of auklets, relatives of guillemots and puffins, have been found in humpback whale scats in the Pacific, so it’s possible that whales in the Celtic Sea swallow seabirds at least inadvertently.

There are two kinds of whale, ones with teeth and ones with sieves known as ‘baleens’. Dolphins such as Fungi and orcas, of Big Willy fame, are toothed. The legendary Moby Dick was a sperm whale, the largest member of the toothed tribe. At least one species, the orca, is an opportunist feeder which takes sea mammals and birds.

Humpbacks, fins, and minkes are baleen whales. They lunge towards their prey, taking a huge amount of water into the mouth. This is released through the baleen, the huge net-like filter made of finger-nail material, which keeps the whale’s victims trapped in the mouth. Fin whales were the likely culprits off Glandore. There were more of them than other whales in the area and they plunge-feed close to the surface. Diving at speeds in excess of 3m/sec, they could pose a risk to birds coming close to them. Minkes and humpbacks move more slowly.

It’s possible, the authors conclude, that lunge-feeding whales ‘could contribute to significant juvenile mortality in seabirds’. Theirs is only the third published paper to address this topic; associations of seabirds and whales have been little researched.

Tracking cetaceans, despite the danger, seems to benefit birds but is there anything in it for the whales? Have relationships developed between particular species? The great whales were hunted to the brink of extinction over the last few centuries. Have seabirds lost the skills needed to feed safely close to them? Whale populations are recovering now. Cetaceans could provide an extra food source for seabirds, at a time when their numbers are declining.

Analysis of scats might reveal whether seabirds are taken routinely by whales. Scats, however, are very difficult to obtain; they break up and sink within half an hour of being passed.