SPRING

Australian Geographic - - Walk About -

Septem­ber–Novem­ber

LITTLE PEN­GUIN NUM­BERS rise rapidly as more and more of these small aquatic birds ar­rive to re­unite with mates from the pre­vi­ous sea­son. “Once the f irst chicks hatch, the par­ents then al­ter­nate go­ing to sea to feed,” says Pro­fes­sor Rob Har­court from Mac­quarie Univer­sity’s Depart­ment of Bi­o­log­i­cal Sciences. “One par­ent al­ways stays with the chicks when they are young, with the other par­ent go­ing to sea for one night. That’s when we can track them, dur­ing these short pe­ri­ods at sea.” When they are on eggs, par­ents can do longer trips of up to 10 days, be­cause they don’t have to feed chicks, although most trips are much shorter.

“If the par­ents are suc­cess­ful they might have a sec­ond clutch through spring and into De­cem­ber,” Rob ex­plains. “They have up to two chicks in a clutch and the chicks grow as big as the par­ents and be­come this big ball of f luff un­til they moult and go to sea. When the chicks start get­ting older, both of the adults can go to sea in search of food be­cause the chicks are more in­de­pen­dent.”

Avian ar­rivals

Mi­gra­tory se­abirds also start ar­riv­ing as the weather starts to warm with the ar­rival of spring. This in­cludes bur­row­ing shear­wa­ters and white-faced storm pe­trels, which choose stands of salt­bush ( Rhago­dia sp) to re-es­tab­lish their nest­ing grounds. The pe­trels have only re­cently be­gun re­colonis­ing Mon­tague and the NPWS is still as­sess­ing how many pairs now use the is­land. Re­cent sur­veys in­di­cate there are about 50 ac­tive bur­rows on the is­land at the mo­ment.

“We’ve re­cently in­stalled a sound-at­trac­tion sys­tem for the pe­trels along with ar­ti­fi­cial nest boxes, which may aug­ment the num­ber at­tracted to the is­land to nest and in­crease their dis­tri­bu­tion into re­stored Rhago­dia habi­tat,” says Amy Har­ris, the south coast’s NPWS shore­bird re­cov­ery co­or­di­na­tor.

The f irst sil­ver gulls and crested terns also be­gin to ar­rive at the is­land dur­ing spring. “They start check­ing out the is­land in Septem­ber, and usu­ally stay longer on land with each pass­ing day, lead­ing up to breed­ing and nest­ing,” Amy says. “In spring they form large so­cial for­ag­ing rafts, com­menc­ing their courtship f lights and dis­plays prior to mat­ing.”

Seals

The great­est seal num­bers oc­cur on Mon­tague dur­ing the spring breed­ing sea­son. “The seals are re­ally in­ter­est­ing be­cause they have this un­usual re­pro­duc­tive strat­egy called em­bry­onic di­a­pause,” Rob says. Males mate with fe­males 7–10 days af­ter the pre­vi­ous sea­son’s pups are born. But, he ex­plains, fer­tilised eggs don’t im­plant in the uter­ine walls of the fe­males un­til months later. In this way pups are timed to be born dur­ing the next breed­ing sea­son, when adult males are pre­oc­cu­pied with fight­ing other males for breed­ing rights.

“It is likely that seals ad­just the tim­ing [of pup births] us­ing this em­bry­onic di­a­pause mech­a­nism to avoid pre­da­tion of pups by the male seals,” Rob says. “They get re­ally ag­gres­sive from about Oc­to­ber through to the end of De­cem­ber when their testos­terone is in full swing. At the end of the breed­ing sea­son their tes­ti­cles shrink right down and their hor­mones turn off and they ba­si­cally turn into eating ma­chines be­cause they haven’t fed dur­ing the breed­ing sea­son, when they have been too busy fight­ing over fe­males.” Males can lose 30–40 per cent of their body mass dur­ing the breed­ing sea­son.

Spring also closes the mi­gra­tory cy­cle of the hump­back whales, which can reg­u­larly be seen at this time of year frol­ick­ing off the is­land with their new­born calves on the southerly leg of their mi­gra­tion to sum­mer feed­ing grounds off Antarc­tica.

The threat­ened sooty oys­ter­catcher breeds al­most ex­clu­sively on off­shore is­lands – in­clud­ing Mon­tague – dur­ing spring and sum­mer.

A sil­ver gull takes to the air above the nest­ing crested tern colony at the base of the Mon­tague Is­land light­house.

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