Vul­tures of the Waves

Although not the pret­ti­est birds to grace the planet, if you ever get the chance to see gi­ant pe­trels in the wild they will command your re­spect like few oth­ers, says re­search sci­en­tist Jamie Cole­man

BBC Earth (Asia) - - Contents - PHO­TOS BY JAMIE COLE­MAN

Sneak a peek at the gi­ant pe­trels, birds that will command your re­spect like few oth­ers

They may not be pretty but they most def­i­nitely are beau­ti­ful in their own un­com­pro­mis­ing way. There is noth­ing quite like watch­ing the com­ing to­gether of hun­dreds of these ma­jes­tic gi­ants at a re­cently de­ceased corpse. With pi­ranha-like ef­fi­ciency, they can tear hun­dreds of kilo­grams of flesh from an ele­phant seal car­cass in hours, with pow­er­ful tube-nosed bills strong enough to crack open a seal skull. Plung­ing deep into the re­mains, the heads and necks of these usu­ally exquisitely preened birds quickly be­come coated with bright red blood and gore. It’s not a sight for the squea­mish!

Equally strik­ing is the com­pe­ti­tion for the op­ti­mal place at the feast. The birds pos­ture with wings spread and tails fanned, mov­ing their heads from side to side while emit­ting their best war songs –

FEW EX­PE­RI­ENCES ARE AS HAUNT­ING AS BE­ING CAST INTO THE SHADOW OF THEIR MAG­NIF­I­CENT 2M WINGSPAN.

chill­ingly prim­i­tive gut­tural cries – to put off challengers. If this de­ter­rent is un­suc­cess­ful the birds clash chest to chest, lock­ing bills and slap­ping wings un­til one con­tender con­cedes. It’s a spec­tac­u­lar dis­play of com­pet­i­tive car­nage from this ul­ti­mate scav­enger.

Yet, in stark con­trast to this sav­age be­hav­iour, these birds are re­splen­dent in flight as they seem to fol­low ships ef­fort­lessly across the South­ern Ocean. “Pe­trels are true masters of the waves with the abil­ity to ma­noeu­vre and thrive in some of the most in­hos­pitable en­vi­ron­ments of the world,” says or­nithol­o­gist David Steel. “It’s no co­in­ci­dence that pe­trels are most nu­mer­ous in lat­i­tudes with per­sis­tent winds. They make fly­ing in the strong­est of weather look easy, as wing adap­ta­tion­slet them ex­ploit the wind’s en­ergy and the air cur­rents that de­velop over steep ocean waves. This al­lows them to travel long dis­tances with lit­tle waste of en­ergy. These seabirds are true pelagic species and their rather short broad tails and often broad-tipped wings give them the ben­e­fits of dy­namic flight.”

AD­MIRE FROM AFAR

Most hu­man en­coun­ters with these pre­his­toric-look­ing birds are from a dis­tance and it is easy to un­der­ap­pre­ci­ate their true size. Side by side, they would com­fort­ably stand taller than a hu­man adult’s knee height. Few ex­pe­ri­ences are as haunt­ing as be­ing cast into the shadow of their mag­nif­i­cent 2m wingspan as you walk along a beach with them soar­ing over your head. The ghostly ‘whoosh’ sounds that ac­com­pany their flight only adds to the su­per­nat­u­ral at­mos­phere.

The Antarc­tic and sub-Antarc­tic is­lands where gi­ant pe­trels breed lack na­tive mam­malian preda­tors, so these birds have ful­filled the twin roles of top preda­tor and top scav­enger. I am cur­rently liv­ing and work­ing on one of these sub-Antarc­tic is­lands, South Ge­or­gia, roughly 1,390km south-east of the Falk­lands and 2,150km from South Amer­ica.

As a prod­uct of its iso­lated na­ture and ex­treme con­di­tions, South Ge­or­gia has no per­ma­nent hu­man res­i­dents. In­stead, it boasts a con­veyor belt of Bri­tish Antarc­tic Sur­vey staff, who in­habit the is­land for a year at a stretch, study­ing fish­eries and Antarc­tic ecosys­tems. It is my re­spon­si­bil­ity to mon­i­tor the suc­cess of the higher preda­tors on the is­land, in­clud­ing Antarc­tic fur seals, wan­der­ing al­ba­trosses, gen­too pen­guins and gi­ant pe­trels. Through­out the south­ern sum­mer, I spend most of my time out in the field col­lect­ing data on their colonies and mon­i­tor­ing their health. Through­out the win­ter, when the pe­trels have de­parted to their win­ter­ing grounds, my fo­cus con­cen­trates on the Antarc­tic fur seals.

My par­tic­u­lar work with gi­ant pe­trels looks at their re­pro­duc­tive suc­cess. I mon­i­tor the birds from when the first adults ar­rive at the colonies un­til the last chick fledges. I record when birds ini­ti­ate breed­ing, how many eggs hatch and when, and the size and weight of the chicks be­fore they fledge. Good feed­ing by the adults re­sults in fat chicks, which have a higher sur­vival rate than lighter chicks. This sort of study gives a rea­son­ably ac­cu­rate im­pres­sion of how healthy the ecosys­tem is, since any large-scale shifts lower down the food chain will sooner or later af­fect the keystone preda­tors, whether in a pos­i­tive or neg­a­tive way.

We have both species of gi­ant pe­trel – south­ern and north­ern – breed­ing on the is­land. As their unimag­i­na­tive names sug­gest, each has a ge­o­graph­i­cally dis­tinct breed­ing range, and they over­lap in South Ge­or­gia. North­ern­ers ar­rive in Septem­ber, just in time for the begin­ning of the ele­phant seal breed­ing sea­son. Their south­ern cousins ap­pear later, just be­fore the Antarc­tic fur seals breed and when pen­guin chicks pro­vide prey and scav­eng­ing op­por­tu­ni­ties. The be­hav­iour of gi­ant pe­trels dif­fers be­tween each penin­sula on the is­land, de­pend­ing on the lo­cal food re­sources, since dif­fer­ent birds in dif­fer­ent ar­eas spe­cialise in dif­fer­ent prey. And in sea­sons where other species fail or strug­gle, these birds pros­per ow­ing to in­creased scav­eng­ing op­por­tu­ni­ties.

Gi­ant pe­trels will also feed on the wing, often with skilled pre­ci­sion to scoop morsels and scraps from the sur­face of the sea, mak­ing them par­tic­u­larly sus­cep­ti­ble to the ac­ci­den­tal in­ges­tion of ma­rine lit­ter. “It’s es­ti­mated that as many as 90 per cent of seabirds have man-made items, such as bal­loons, in their stom­achs,” says David Steel.

Both species are largely monog­a­mous. They lay a sin­gle egg ev­ery year, which is in­cu­bated for two months. Chicks are born white-grey and downy, but be­fore they fledge at four months old they moult this down and re­place it with darker feath­ers. As they age, most of them grad­u­ally be­come paler. Af­ter hatch­ing, the chick will be guarded by one par­ent while its mate finds food, but they grow rapidly and within only three to four weeks both adults can head out to for­age, leav­ing the chick to fend for it­self – very ably.

From afar the chicks may look vul­ner­a­ble – but this is by no means the case. Most pe­trels cre­ate

IN THE SOUTH­ERN HEMI­SPHERE THOU­SANDS OF PE­TRELS ARE KILLED BY HOOKS ON LONGLINES.

an en­ergy-rich oily sub­stance as a biprod­uct of di­ges­tion, which they are able to store for pe­ri­ods when without food. How­ever, if re­quired, this dis­gust­ingly pun­gent glop can be ejected over large dis­tances to ward off an at­tack from the likes of a skua. It may not sound like much of a weapon, but the oil binds to feath­ers and can cause per­ma­nent dam­age. It also binds to cloth­ing and skin, as I know to my cost.

Sadly, smelly glop is no de­fence against the im­pact of the fish­ing in­dus­try. In the south­ern hemi­sphere many tens of thou­sands of pe­trels and al­ba­trosses are need­lessly killed by long­line fish­ing fleets. Longlin­ing is a method in which fish­ing lines with thou­sands of baited hooks at­tached are set over the side of a ship into the wa­ter col­umn and left to catch tar­geted prey over a pe­riod of time. This prac­tice is as­so­ci­ated with the by­catch of many seabirds as well as non-tar­get fish species: the baited hooks make very ap­petis­ing look­ing meals for birds, which get hooked and dragged be­neath the sur­face where they drown.

A GLOBAL PROB­LEM

The good news is that in South Ge­or­gian wa­ters, with the help of the Con­ven­tion for Con­ser­va­tion of Antarc­tic Ma­rine Liv­ing Re­sources, al­ter­na­tive fish­ing methods have been put in place to re­duce by­catch. These have been a great suc­cess, re­duc­ing the in­ci­den­tal death of seabirds from thou­sands ev­ery year in the late 1990s to al­most nil cur­rently. Other fish­eries are now be­ing en­cour­aged to in­tro­duce these sim­ple mod­i­fi­ca­tions. Un­for­tu­nately, how­ever, many pelagic seabirds have mas­sive ranges and so they sim­ply end up in fish­ing ar­eas that re­main less well-po­liced and where by­catch is still too high.

Hope­fully we’ll find a way to help gi­ant pe­trels thrive across the South­ern Ocean for cen­turies to come. In the mean­time, I feel priv­i­leged to get up close and per­sonal with these amaz­ing – if some­what grue­some – birds. Af­ter a day in the field with them I’ve often re­turned to base bleed­ing from mul­ti­ple peck wounds and smelling like noth­ing on Earth, and sev­eral washes later may still be asked to sit at a ta­ble on my own for din­ner. But it’s worth it.

South­ern gi­ant pe­trel chicks are raised with a spec­tac­u­lar

sea view. Af­ter fledg­ing, ju­ve­niles spend their first few years on an ex­ten­sive cir­cum­nav­i­ga­tion of the

South­ern Ocean.

BE­LOW: When rear­ing chicks, the pe­trels rely heav­ily on pen­guin and seal colonies as a source of food

ABOVE: Gi­ant pe­trels are sim­i­lar in size to many al­ba­trosses, but have nar­rower, shorter wings.

CLOCK­WISE

FROM TOP: Two gi­ant pe­trels fight over food; the birds raise their chicks on bare or grassy ground in colonies; feed­ing on car­casses is a messy busi­ness; gi­ant pe­trels are largely scav­engers

RIGHT: There are two colour morphs, white and dark. Young of the dark morph, as here, are sooty black

LEFT: With their meat-cleaver bills, gi­ant pe­trels have pres­ence

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