SPRING
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.