(CNN) After nearly being hunted to extinction, southern right whales in Australia are making a comeback -- with the help of drones.
Researchers from Australia's Murdoch University have teamed up with the World Wide Fund Australia and are using drones for the first time to check on the health of the endangered species.
They're monitoring southern right whales in the Great Australian Bight and have revealed that females lose an extraordinary amount of weight while fattening up their calves, before journeying back to Antarctica.
The whales travel thousands of miles to the area off South Australia's coast to give birth. Researchers have found that, once the calves are born, mothers do not eat and rely solely on their fat stores.
Scarlet with suspected propeller cuts from a large ship.
WWF-Australia whale researcher Chris Johnson said their significant weight loss made them "especially vulnerable to emerging threats."
Global ocean warming -- which can reduce their food supply, tangling in marine debris, increased ship traffic and oil and gas exploration all threaten the endangered species.
"Nurturing a calf is already tough enough for the mothers without humans adding to the pressure," Johnson said.
That's why, he said, the research project involving drones is so important. "If the condition of the whales changes in the future, it could be a sign that human activities are having an impact."
One drone picture revealed that a southern right whale mother, named Scooter, lost 17 inches in body width in as little as two months while looking after her calf. Other mothers became so skinny, even their spinal cords began to show.
Scooter on July 3 (top) and September 4 (bottom). She lost 17 inches (43 centimeters) in width in 63 days
Lead researcher Fredrik Christiansen from Murdoch University said whale mothers could only give birth every three to four years because of the toll on their bodies.
"When they arrive, they have significant fat reserves; they are wide all along their body. When they leave, they look like giant tadpoles. They have a head which is still big and robust, but the rest of the body is skinny, and you can even see the spinal cord showing up,"
Professor Lars Bejder, also from Murdoch University, told CNN that little was known about mother-calf relationships, so the study helped researchers understand the general consequences of reproduction for these mammals.
He said as female whales only return every three to four years, it was crucial for the research to carry on: "It's important we do it for another 2-3 years to get a full sense of all the moms which will give us a really good indication (of the impacts of breeding)."
Bejder said it's also important for the team to start looking at Antarctica, where southern right whales migrate to after breeding, to understand their feeding habits.
Spokesman, Mark Symons, for WWF-Australia said it was the "first time scientists have been able to study whales in this way."
He said WWF-Australia sponsored the research and that drones were able to "unlock some of their mysteries."
Bella's calf on July 3 (top) and September 4 (bottom). The calf grew 6 feet (1.83 meters) in length in two months.
Whaling in the 19th century almost wiped out the entire species in Australian waters, leaving less than 300 remaining. Fortunately the particular species are no longer hunted and researchers now estimate numbers have increased to 3,500. But still, they said, there's much to learn.
"Southern right whales are recovering but nowhere near to the same extent as humpback whales. And we don't really know why, and that's one of the big questions we're hoping to answer," Bejder said.
"(They're) magnificent animals and a symbol of ocean health so it's really important that these animals are conserved in their natural environment."
Endangered no more: Animal species on the rebound
Here's a look at other rare animals whose once-dwindling populations have rebounded. The inspiration for the teddy bear, the Louisiana black bear, will be delisted as a threatened species on March 11, 2015. The bear was originally listed under the Endangered Species Act in 1992 due to habitat loss.
Citing significant improvements in its population and habitat conditions and reductions in direct threats,
the U.S. Fish and Wildlife Service proposed downlisting the West Indian manatee from "endangered" to "threatened" under the Endangered Species Act.
Thanks to conservation efforts by states, landowners and others, the Delmarva Peninsula fox squirrel -- native to Mid-Atlantic states -- is no longer at risk of extinction. One of the animals included on the first list of endangered species nearly a half-century ago, the squirrel was set to be removed from the list in December 2015, the U.S. Department of the Interior said.
Columbian white-tailed deer, native to Oregon and Washington, were officially listed as endangered in 1967. They were removed from the list in 2003 after the population grew from less than 2,000 to more than 5,500.
The Lake Erie water snake, native to the Great Lake's waters between Cleveland and Toledo, Ohio, was removed from the endangered species list in 2011. The snakes grow to more than 3 feet in length and are not venomous.
A gray whale calf emerges from the waters off Baja California, Mexico, in 2010. The Pacific gray whales have been protected since 1970 and are at the center of a growing whale-watching industry. They were removed from the endangered species list in 1994, although climate change has impacted their food chain and caused their numbers to decline again in recent years.
The Steller sea lion, native to Alaska, was removed from the list in 2013 after 23 years of federal protection.
The Virginia northern flying squirrel was in danger of extinction in 1985, when scientists documented only 10 remaining animals. But its population made a comeback, and the squirrel was removed from the list in 2013. The squirrel is native to West Virginia and, yes, Virginia. It doesn't really fly, although membranes between its legs serve as "wings" and let it glide from tree to tree.
The American alligator was placed under federal protection in 1979 and removed eight years later thanks to limits on alligator hunting, which had depleted the species.
The gray wolf, which can be found in wilderness areas of the northern American West and Canada, was listed as endangered in 1978. After its populations recovered, the wolf was taken off the list in 2011.
The red kangaroo, the largest of all kangaroo species, is of course native to Australia's arid outback rather than the United States. According to a list released by the U.S. Fish and Wildlife Service, it was added in 1974 and delisted in 1995.
The American peregrine falcon was classified as endangered in 1970 after its population was decimated by pesticides. By 1975, there were only 324 known nesting pairs of American peregrine falcons. Conservation efforts helped them rebound, and they were removed from the list in 1999. There are now more than 2,000 known breeding pairs of the birds in North America.
Adult brown pelican, found in the coastal Atlantic and the Gulf of Mexico, can reach up to 8 pounds and have wingspans of over 7 feet. The birds were listed as endangered in 1970 but taken off the list in 2009.
The bald eagle, a revered American national symbol, was famously endangered for 40 years. By 1963, only 417 known nesting pairs of bald eagles remained in the U.S. Vigorous conservation efforts revived the handsome bird, and it was removed from the list in 2007. Today there are more than 10,000 nesting pairs of bald eagles in the contiguous United States.
The Aleutian Canada goose, found in Alaska, Canada and the Pacific Northwest, numbered only in the hundreds in the mid-1970s. But efforts to recover the bird population were successful, and biologists estimated that there were 37,000 Aleutian Canada geese by the time the bird was removed from the list in 2001.