The lava birds

Meet the Me­lane­sian megapode – an avian species that starts life be­neath the warm sands of the vol­canic Solomon Is­lands.

BBC Wildlife Magazine - - Contents - By Mark Cocker Pho­tos David Ti­pling

Dis­cover the an­cient Me­lane­sian megapodes that use sub­ter­ranean vol­canic heat to in­cu­bate their eggs

The sound of our boat’s en­gine drowned out the vast si­lence of the South Pa­cific night. It was 4am and pitch black – the only thing I could see dis­tinctly was the white­ness of the break­ers crash­ing and spread­ing onto the shore.

We were on the Solomon Is­lands, at a place called Savo, to see a bird that lays its eggs in the ground, like a croc­o­dile. The em­bryos are warmed by the heat of vol­ca­noes. When they hatch, the chicks, alone and un­aided, have to scram­ble up – some­times through 1.5m of sand – from the nest-grave in which their moth­ers have buried them. Par­ent and off­spring will never know­ingly meet.

The crea­ture in ques­tion is called the Me­lane­sian megapode – a ground-dwelling species, about the size of a chicken, with a small head, short brown wings and a spher­i­cal body that car­ries a deep, dark blue­black sheen. Its most no­table fea­ture is the size of its legs and feet, which ex­plains that odd name – megapode means ‘big foot’.

Megapodes form a sep­a­rate an­cient fam­ily called the Me­gapodi­idae that in­cludes 22 species, which oc­cur from the In­dian Ocean across parts of In­done­sia, the Philip­pines and

New Guinea, as far as south­ern Aus­tralia, then way out into the cen­tral Pa­cific through the ar­ray of is­lands known as Me­lane­sia. Savo is among that com­plex of ar­chi­pel­a­gos and it is no co­in­ci­dence that this spot, like much of the zone in which megapodes oc­cur, ex­pe­ri­ences some of the high­est lev­els of seis­mic ac­tiv­ity known on Earth.

Savo is a live vol­cano and the megapodes have prob­a­bly ex­ploited the is­land’s sub­ter­ranean heat to in­cu­bate their eggs for mil­len­nia. In turn, the lo­cal peo­ple have learned to ex­ploit this re­la­tion­ship to sup­ply them­selves with some of the most nu­tri­tious eggs pro­duced by any avian species.

We were still in semi-dark­ness when Wil­fred Ngasi, the chief of Aga­toka vil­lage, ush­ered me and pho­tog­ra­pher David Ti­pling to a beach bor­der­ing the for­est, where the megapodes lay. The lo­cals make th­ese sand­fields even more at­trac­tive for the birds by clear­ing fallen de­bris, while a thatched fence around the perime­ter ex­cludes preda­tors, such as pigs, dogs and mon­i­tor lizards. Even as we took our seats be­hind the ‘blind’ we could hear the megapodes in the trees over­head, where they pro­duced a loud, high-pitched cho­rus of ‘yee-yeeow’ notes.

Beach bur­row­ers

Lo­cal tra­di­tion has it that Savo’s birds come from Guadal­canal, the largest of the Solomon Is­lands, about 15km to the south. In truth, they prob­a­bly come from all di­rec­tions and many is­lands, since sites with the nec­es­sary geo­ther­mal con­di­tions are ex­cep­tional. There is one Me­lane­sian megapode nest­ing ground called Pok­ili, on the is­land of New Bri­tain, that drew in an es­ti­mated 53,000 birds in a sin­gle sea­son dur­ing the 1970s. Such is the im­por­tance of th­ese spots that, in the past, peo­ple fought run­ning bat­tles over con­trol of them, some­times with fa­tal con­se­quences.

At Savo, the neigh­bour­ing vil­lagers reg­u­late their megapode fields am­i­ca­bly. Soon the birds were run­ning freely across them to be­gin their morn­ing’s work. It was

In less than a minute, a megapode would go from full view to van­ish­ing into its own ex­ca­va­tions.

at this point that those re­mark­able feet came into their own. Find­ing a suit­able spot, a bird would set to rak­ing hard and, in less than a minute, could go from full view to van­ish­ing com­pletely into its own ex­ca­va­tions. The scene was one of as­ton­ish­ing in­dus­try ac­com­pa­nied by a re­lent­less hub­bub of high con­tact notes.

The megapodes un­der­took ad­ja­cent dig­gings and puls­ing jets of scraped sand would fly into the air in se­quence. Each ex­ca­va­tion pro­ceeded in a rhyth­mic pat­tern but of­ten with the spoil arc­ing in di­a­met­ri­cally op­posed di­rec­tions. Sev­eral birds would oc­ca­sion­ally be busy all in one patch, but out of sight, and it would ap­pear as if the ground were mag­i­cally dig­ging it­self.

As it goes deeper, a megapode has the chal­lenge of re­mov­ing the spoil that has ac­cu­mu­lated at the mouth of its hole. It must rou­tinely emerge to clear th­ese tail­ings be­fore re­turn­ing to the ‘coal-face’.

Hid­den depths

Later in the day, we were present when lo­cal peo­ple dug out the re­sult­ing cav­i­ties and it was as­ton­ish­ing to see the depths to which this 550g bird had de­scended. In an at­tempt to re­trieve one of th­ese eggs, some peo­ple would van­ish head-first into a bur­row with only their feet show­ing.

It was in­trigu­ing to find that the bot­tom of the hole was moist and warm; it is thought that megapodes pos­sess sen­si­tive parts in their mouths or tongues that help them judge the sub­strate’s tem­per­a­ture. The nat­u­rally oc­cur­ring heat vent slowly in­cu­bates the egg and the chick emerges about 50 days later. In some species of megapode, such as the Aus­tralian malleefowl, eggs have hatched af­ter 90 days. For com­par­i­son, the av­er­age do­mes­tic chicken takes fewer than 30.

The fam­ily, as a whole, uses two other meth­ods of in­cu­ba­tion aside from mak­ing the most of geo­ther­mal ac­tiv­ity. Three species use beaches that are warmed sim­ply by the sun, but the most com­mon strat­egy is to ex­ploit heat gen­er­ated by the mi­cro­bial de­com­po­si­tion of veg­e­ta­tion. Me­lane­sian megapodes also use this method.

Clock­wise from left: Megapodes ex­ca­vate their nest cham­bers; th­ese 550g birds can dig to im­pres­sive depths; there can some­times be a bit of a skir­mish among the birds, as they look for suit­able dig­ging spots; vol­cani­cally heated sand re­sults in com­mu­nal nest grounds; Savo Is­land.

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