A 4.8 m male estuarine crocodile ready for release with satellite transmitter. This crocodile traveled over 590 km by sea. (Courtesy/University of Queensland)
Next time you’re out sailing the high seas and think you’ve spotted a crocodile hanging ten, no need to get your eyes checked just yet. Turns out crocs do surf ocean currents, albeit sans boards and all the crazy wipeouts.
The behavior tracked by researchers out of Queensland, Australia, helps explain why the reptiles are so widespread, yet genetically similar.
Estuarine crocodiles which typically live in saltwater habitats like rivers and mangroves occupy a range covering about 10,000 km2 stretching from East India to Fiji and southern China to northern Australia, said the study. Geographic isolation tends to support the evolution of different species. But despite living in places separated by thousands of miles of open ocean, a crocodile living in Fiji is likely the same kind of croc living in Australia.
“The estuarine crocodile occurs as island populations throughout the Indian and Pacific Oceans, and because they are the only species of salt-water living crocodile to exist across this vast area, regular mixing between the island populations probably occurs,” said Hamish Campbell with the University of Queensland, and study lead in a press release.
But until now, scientists weren’t sure how. Stories have floated in over the years of ocean-bound crocodiles, even though the toothy predators are no Mark Spitz when it comes to swimming. Campbell and his colleagues from Queensland Parks and Wildlife Service and Australia Zoo set out to monitor the mobile capacity of crocs. They used acoustic and satellite tracking to follow the movements of 27 adult crocodiles over the course of a year. The crocodiles revealed an astonishing range of movement, regularly traveling 50 kilometers or more from their stomping grounds to the mouth of the river and out into the sea.
Croc’s, it seems, like to “go with the flow,” according to the researchers. Tides and currents dictate the timing and extent of a crocodile’s swim, with crocs typically beginning a swim within an hour of a changing tide, following the movement of the water, and returning to shore when water is no longer headed in the desired direction. Similar behavior applies to swims in the open ocean, where crocs ride the currents.
One croc, a roughly 15-foot- long male, traveled more than 400 kilometers in 20 days from the east coast of Cape York Peninsula through the Torres Straits to the west coast of Cape York, according to the study. At one point, the croc stopped on the shore of the Torres Straits and stayed there for four days waiting for more ideal currents.
Campbell explains that this type of behavior, “not only helps to explains how estuarine crocodiles move between oceanic islands, but also contributes to the theory that crocodilians have crossed major marine barriers during their evolutionary past.”
The full paper is available in the British Ecological Society’s Journal of Animal Ecology.
Two girls in a jeep rumble around the country roads of Nebraska to check out the spring sandhill crane migration and can’t believe their eyes. Be careful. Watching this might make you a craniac.
Going organic isn’t just a popular choice for eco-savvy dieters, turns out migratory birds like it too. A new study out of Lund University in Sweden shows that migrating birds lean towards green when it comes to large-scale monoculture farms, with higher abundances and diversity of birds choosing to stop at organic farms than conventional ones. The findings offer new crops for thought when it comes to managing agriculture for wildlife well-being.
The idea that organic farming is good for wildlife is nothing new. Farming practices that hit overdrive and heavy pesticide use have been linked to drops in wildlife populations. But previous studies focused largely on bugs or resident bird populations. Juliana Dänhardt and Martin Green of Lund University decided to take the research a step further, focusing on migratory bird species.
Migratory birds get hit with a double whammy when dealing with environmental stress. They contend with a lot of the same environmental pressures as resident birds, but enjoy the added baggage that comes from moving into a temporary living situation. These visitors tend to show up at tilling time to an unfamiliar landscape and must fuel up in a hurry before embarking on the next leg of their journey.
Dänhardt and Green wanted to see if organic farming and more diverse cropland would helped alleviate some of these pressures. In 2005, they and their team selected a dozen pairs of farms in Falsterbo, Sweden, one of the richest agricultural regions of the country. The pairs were set up to compare organic versus conventional and diverse versus simple crop farms. During the fall migratory season, they conducted bird surveys to see what happened. Dänhardt and her colleagues found the relationship between birds and farm preference to be a complicated one.
The strength of bird populations was all over the show. Some types of birds did prefer diverse organic farmland, while others were less discerning. And certain species, such as geese and golden plovers, showed a penchant for wide-open monoculture fields. But one overarching trend did emerge from the complexity. Turns out, birds that chose the wide-open fields also preferred the organic version.
At the moment, ag trends in Sweden lean towards encouraging crop diversity as a way to bolster wildlife populations, but this study indicates that supporting organic or low-impact farming practices on large-scale monoculture farms could be another method for helping out those hard-flying, fast-eating, stressed out migratory birds.
The study is published in the online early edition of the journal Oikos.
Along the Yucatan Peninsula, in a land of heat and drenching humidity thrives a rare mangrove ecosystem, important for coastal life and home to jaguarundi, hundreds of bird species and, yes, maybe a mosquito or two. I hope you enjoy this short jaunt into the mangroves, sans the mosquitoes, near Celestun in Mexico’s Yucatan Peninsula. One afternoon doesn’t do a place like this justice, but it is a glimpse into this vulnerable ecosystem that is increasingly under threat from climate change, deforestation, pollution and coral reef degradation.
Every year the horseshoe crabs gather to spawn, releasing thousands of eggs along the Delaware Bay coast. And with timing perfected by evolution, red knots, a bird enduring one of the most impressive yearly migrations from the Arctic to the Tierra del Fuego, arrive just in time to gorge on the eggs of the horseshoe crab. It is a vital stop on the “peeps'” spring migration. But the crabs and their eggs are disappearing, a loss with dire consequences for the little birds.
Red knot populations have fallen more than 75 percent in recent years, and new research published in this month’s issue of Bioscience reveals that Red knots can thank the bait fisheries for their hungry stomachs. Within half a decade the fisheries harvesting horseshoe crabs grew 20-fold, gobbling up more than 2 million crabs a year and effectively eliminating 90 percent of the eggs that red knots rely upon to survive their almost 19,000 mile migration.
But this research is not just a blame game for the fisheries. A coalition of scientists worked together on this study to help draft recommendations for the adaptive management of the bait fisheries that could help all three groups survive.
For a month after birth, Southern right whale mothers and their calves rest and nurse. Then, like the pair shown here off Argentina, they start to swim faster and farther as they prepare for a long migration in the South Atlantic to reach their feeding areas. A University of Utah study found mother whales teach their calves where to eat, raising concern about whether the whales can adapt as global warming disrupts feeding grounds. (Photo/John Atkinson, Ocean Alliance)
Mom right whales know best when it comes to mealtime it seems. They lead calves to grub at traditional feeding grounds teaching their offspring generations of knowledge about when and where to find food. In fact whole clans of whales will dine together in the cetacean version of a family-owned dining spot. But this is one family tradition that could lead to starvation for an already vulnerable whale species if climate change causes shifts in food distribution.
Previous research by Vicky Rowntree, research associate professor of biology and a coauthor of the new study at the University of Utah, has already shown the impacts of climate change on right whale populations. When sea temperatures rise, krill disappear and right whales respond by giving birth to fewer offspring. Now these new studies into whale behavior could highlight another problem for the whales when it comes to food.
“A primary concern is, what are whales going to do with global warming, which may change the location and abundance of their prey?” asked Rowntree in a press release. “Can they adapt if they learn from their mother where to feed – or will they die?”
Rowntree and her colleagues collected skin samples from right whales and, using a novel technique in science, combined DNA and isotope analysis to determine whale lineages and where they tend to chow down. They found that related whales congregated in designated areas to feed, and that mothers teach calves in their first year of life where to find food.
Here’s to hoping that right whales will be quick to adapt if the buffet moves elsewhere.
The Nature Files 