bubbling under The hidden lives of seabirds

Text by Steve Benjamin & Lauren de Vos

Photographs by Jean Tresfon enowned for the shoals of fish that tempt top marine predators along the Gannets breed at only six sites in southern Africa, namely Possession, Mercury and South African coastline, the so-called sardine run has attracted much interest Ichaboe­ islands in Namibia and, in South for the shark and cetacean behaviour associated with it. Less publicised, Africa, Bird Island at Lamberts Bay, Malgas R Island and Bird Island in Algoa Bay. The last how­ever, are the underwater exploits of these predators’ avian counterparts. is the largest colony and in 1994 supported 68 000 pairs of gannets. Weighing 2.6 kilo- Steve Benjamin found himself distracted from the shimmering shoals by the antics of grams and with a 1.8-metre wingspan, the Cape Gannet is a large bird and its terrific Cape Gannets and Cape Cormorants and discovered that these birds are adapted power is evident as it plunges from a dizzy- to dominate both sea and sky. Lauren De Vos captures his adventures in text. ing height. Wings back and neck exten­ded, it becomes a ‘beaked bullet’ moments be- fore impact with the water at 90–100 kilo­ he turbulent waters off South metres an hour. As proficient underwater Africa’s coast boast a spectacu- as it is in the air, the gannet can dive to a lar array of marine life and play depth of 10 metres, its trajectory traced by host to diverse aerial predators a contrail of bubbles. As numbers of gan- thatT hone their skills wheeling in the skies nets hit the waves, divers’ ears ring with above. Determined competition among the noise of a battlefield – ‘cannons’ firing these masters of sea and sky has driven and ‘bullets’ whistling through the blue. Cape Gannets Morus capensis and Cape In a fascinating inversion of their above- Cormorants Phalacrocorax capensis to be- water behaviour, the birds spread their come efficient underwater pred­­ators that wings and ‘fly’ to greater depths (plung- target sardines and other baitfish. Plum- ing as deep as 22 metres) in pursuit of fish. meting from a considerable height, the But this specialised hunter, now classified Cape Gannet performs fearless high-speed as Vulner­able, faces a threat to its survival: dives. With a breath-hold that would ren- the 80 per cent population decrease since der free-divers green with envy, the Cape the 1950s has been attributed largely to the Cormorant doggedly pursues its prey at over-exploitation of fish stocks by humans, depth. But the under-water­ interactions and there is keen competition by prey between these two species are difficult to species for the diminishing food resources. observe and not widely documented. It is A glossy blue-black bird with a striking a unique series of events and the perfect orange gular pouch, the Cape Cormorant synchrony of con­ditions that uncover is smaller than the gannet, weighs 1.2 kilo­ their underwater skirmishes as they take grams and is well adapted to long dives in on one another,­­ fellow predators and the pursuit of its fish prey. Although its popu- elements. lation is declining and it is categorised as There is one occasion that most signifi­ Near-Threatened, it is common along the cantly draws these species together in Cape West Coast in both inshore marine their battle for a prized common resource environments and inland fresh­water sys- and, fortuitously, it is the same event that tems, with the core of its range stretching allows phenomenal opportunities for hu- south from Cape Cross in Namibia to Cape man observation of their interactions. On Agulhas. Here the cormorants can be seen the annual sardine run, divers have the in their thousands as they ‘leap-frog’ one chance to watch these birds underwater as another to chase prey. They are less popu- they prey on static sardine bait-balls (tight lous along the Eastern Cape coast, but a phenomena. Each year between May Above A Cape Gannet brakes at the formations of fish trying to escape preda- few hundred birds roost on the sheer cliffs and July millions of sardines leave their conclusion of a successful dive. tion). My understanding of and respect near Port St Johns. They are well adapted feeding grounds off the Eastern Agulhas for these birds grew immensely during for chasing fast-moving fish and use their banks and embark on a spawning migra- Opposite A model of aerodynamic design, last year’s run when, together with pho- large, webbed feet to propel themselves tion that takes them up the KwaZulu- a gannet arrows out of the sky in pursuit tographer Jean Tresfon, I witnessed spec- through the water. These birds are in fact Natal coastline. The fish travel within of fish harried to the surface by common tacular feats of agility, determination and quite heavy relative to their body size, an a cold finger of water that creeps up the dolphins. perseverance. Dominating both realms of adaptation that helps them to remain un- coast and facilitates their movement. They blue, from the sky to the sea, Cape Gan- derwater for up to 76 seconds at a time. can cover as much as 60 kilometres a day, Previous spread The underwater battle nets and Cape Cormorants displayed their in pulses comprising many small pockets zone explodes as common dolphins charge prowess as avian predators and revealed he sardine run, off South Af- or in a massive shoal that resembles an oil through a shoal of red-eye herrings. A Cape their secret underwater lives. rica’s tempestuous Wild Coast, slick. Greatly influenced by ocean condi- Gannet bullets through the water, bubbles Distinguished by their bright blue eye­ is considered to be one of the tions, they are not observed at all in some streaming in its wake. rings and creamy white plumage, Cape Tworld’s most spectacular natural years, possibly because they pass the 44 seabird submariners AFRICA – BIRDS & BIRDING april/may 2012 seabird submariners 45

coastline at some depth and away from n last year’s run, in crystal- at a time that I really saw what the birds a strike rate as the gannets. Their talent, it Above A pair of streamlined Cape Do diving Cape predators’ scrutiny. clear water 10 metres below were doing during their dives. Targeting appeared, lay in robbing one another­ – and Cormorants are clearly intent on a meal as Unsurprisingly, an army of marine ma- the churning surface, a bait- a specific fish as they plummeted out of the gannets. With their smaller bodies, cor- they penetrate the shoal. Gannets ever rauders pursues these rich, oily fish and, ball of red-eye herring and the air, the gannets could deftly alter their morants are agile swimmers and faster than prizing them as a meal, the predators sardinesO glittered and swirled in a bid to trajectory as they catapulted themselves the heftier gannets underwater. Often, a Opposite Three Cape Cormorants gang up hit divers? go to great lengths to gorge themselves escape the barrage of predatory action through the water. A number of the birds black smudge of paddling cormorants har- on a Cape Gannet in a bid to wrest its hard- in the brief time of plenty. Long-beaked from common dolphins, Cape Gannets exited their dives upside-down, with a fish assed gannets that had failed to swallow won catch from it. ape Gannets are highly sensitive to common dolphins can form super-pods of and Cape Cormorants. Photographers were grasped in their bill. To achieve this, they their oily prize quickly enough. On one oc- Chuman activity around bait-balls. up to 5 000 individuals as they travel in there, primed to capture images of the had to keep the prey in sight throughout casion I watched as, like a band of impa- Previous spread If you can’t catch a fish, If observed from a distance, the birds search of the sardine shoals, while squad- frenzied action. Cormorants raced around the dive. They often seized the sardine tient underwater mobsters, 10 cormorants steal one. A pair of gannets tussle over a continue to plummet out of the sky as rons of tens of thousands Cape Gannets like wind-up toys between the fleeing midway along its body or by the tail and aggressively latched onto a single gannet as red-eye herring. they feed, but once snorkellers enter follow them closely from above. Below fish, paddling their webbed feet to propel then, after flicking the fish around under- it fought its way to the surface in a vain bid the water the gannets generally stop the surface, unknown numbers of cop- themselves through the confused blur of water, they would hastily gulp it down. to retain possession of its sardine. diving and move away. On occasion, per and dusky sharks congregate along silver scales. Often one fish was not sufficient and Flurries of activity such as this boil just they continue to dive if the bait-ball is the inshore waters in anticipation of the A symbiotic pattern emerged: first, the the gannets would pursue one another to below the surface of the water and the large or if they are particularly hungry, sardines. All the species rely on this huge common dolphins rallied and raced to- steal catches. Alternatively, an individual epic battles remain hidden from general which can occur after long periods of food resource and their life cycles are wards the fish, causing a shimmer of panic. would keep going, pumping its wings and view. The birds’ patience, skill and deter- extremely rough weather or a lack of timed to take advantage of its abundance. The high-pitched clicks and whistles sig­­- feet to chase down more fish. These birds mination are tested to the limit as they fish moving into the area. The risk Predictably, the occurrence of the sar- nalling this cetacean charge were followed don’t give up easily: divers have witnessed not only clash with one another, but fend of injury as a result of colliding with dine run draws wildlife photographers by a gannet blitzkrieg as hundreds of white, a single gannet catch and consume three off a host of other specialised marine pred­ an unpredictable moving object (such and adventure divers from around the feathered streaks bombed the water and fish during one plunge. ators in order to eat and survive. Ironical- as a snorkeller) in their feeding zone world. Unlike the predators, the ultimate seized the bewildered fish. Meanwhile, in a Cormorants employ a very different ly, their feathered appearance belies their is clearly one that is not worth taking. prize for the divers is not a meal but the clean-up action, opportunistic cormorants­ tactic to hunt their prey. Descending into prowess as highly adapted swimmers and The birds may continue to dive if a opportunity to witness a bait-ball wrestled lunged at potential escapees. the swirling shoal, they swim hard and ex- divers that are able to compete on a par small number of scuba divers are by a host of top predators. It’s easier said Given the lightning speed at which the tend their necks to grasp hold of fish. Al- with their shark and cetacean counter- underwater and near the bait-ball. than done and it can take many expedi- events occurred, it wasn’t until I reviewed though they were dogged in their pursuit, parts. It truly seems to be a secret life that tions before this goal is realised. photographs and video footage one frame these birds did not appear to have as high seabirds lead.

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