screenshot from infrared video by Animal Energetics / Powers Lab
screenshot from infrared video by Animal Energetics / Powers Lab

Infrared Video Shows How Hummingbirds Shed Heat Through Their Eyes and Feet

screenshot from infrared video by Animal Energetics / Powers Lab
screenshot from infrared video by Animal Energetics / Powers Lab

Animals have lots of ways of keeping cool. Dogs pant, humans sweat, koalas hug trees. But what about birds? Flying generates lots of heat, and getting rid of the excess is complicated when your body is covered in insulating feathers.

Ecologist Donald Powers is interested in how hummingbirds regulate heat. The tiny birds can hover in the air and fly at speeds up to 39 feet per second (and some can hit about 88 feet per second while diving), beating their wings 80 times per second. The range of speeds, Powers figured, means they probably employ a few different ways of losing heat.

To find out what those are, he and other researchers used an infrared camera to measure the heat lost by calliope hummingbirds flying in a wind tunnel.

As they recently described in a study published in Royal Society Open Science, the team discovered that the birds have a few key heat dissipation areas (HDAs) that were consistently 46°F or more above air temperature during flight. These spots were around their eyes, under their wings, and on their feet—all areas where feathers are sparse or absent and heat can be shed easily. They appear as bright white spots on the hovering hummingbird in the infrared thermography video below.

The different HDAs came into play at different flight speeds. The hot spots around the birds’ eyes, for example, were three times larger during hovering and slow flights than they were during faster flights. While hovering, the birds also dangled their legs instead tucking them in like they do during faster flights, maximizing their heat loss. The HDAs under the birds wings, meanwhile, were largest and highest in temperature at the lowest and highest flight speeds when the wing muscles were working hardest.

All of this suggests that, as Powers predicted, hummingbirds use different heat loss mechanisms depending on how fast they're flying, with most heat lost through radiation at lower speeds, and convection becoming more important at higher speeds. It also suggests that hummingbirds have the hardest time maintaining a normal temperature while hovering, which requires more metabolic power and exposes the birds to less airflow.

When it’s cold out, hummingbirds have to worry about regulating their temperatures the other way and keep themselves from losing too much heat. To stay warm in the winter, the birds slow their metabolisms down and go into torpor. Many species also head to warmer parts of the world, like the Rufous hummingbird, which usually lives in Canada and Alaska and spends winters in Mexico and the Caribbean.

Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5
Climate Change Has Forced Mussels to Toughen Up
Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5
Andreas Trepte via Wikimedia Commons // CC BY-SA 2.5

Researchers writing in the journal Science Advances say blue mussels are rapidly evolving stronger shells to protect themselves against rising acid levels in sea water.

Bivalves like mussels, clams, and oysters aren’t good swimmers, and they don’t have teeth. Their hard shells are often the only things standing between themselves and a sea of dangers.

But even those shells have been threatened lately, as pollution and climate change push the ocean's carbon dioxide to dangerous levels. Too much carbon dioxide interferes with a bivalve’s ability to calcify (or harden) its shell, leaving it completely vulnerable.

A team of German scientists wondered what, if anything, the bivalves were doing to cope. They studied two populations of blue mussels (Mytilus edulis): one in the Baltic Sea, and another in the brackish waters of the North Sea.

The researchers collected water samples and monitored the mussel colonies for three years. They analyzed the chemical content of the water and the mussels’ life cycles—tracking their growth, survival, and death.

The red line across this mussel larva shows the limits of its shell growth. Image credit: Thomsen et al. Sci. Adv. 2017

Analysis of all that data showed that the two groups were living very different lives. The Baltic was rapidly acidifying—but rather than rolling over and dying, Baltic mussels were armoring up. Over several generations, their shells grew harder.

Their cousins living in the relatively stable waters of the North Sea enjoyed a cushier existence. Their shells stayed pretty much the same. That may be the case for now, the researchers say, but it definitely leaves them vulnerable to higher carbon dioxide levels in the future.

Inspiring as the Baltic mussels’ defiance might be, the researchers note that it’s not a short-term solution. Tougher shells didn’t increase the mussels’ survival rate in acidified waters—at least, not yet.

"Future experiments need to be performed over multiple generations," the authors write, "to obtain a detailed understanding of the rate of adaptation and the underlying mechanisms to predict whether adaptation will enable marine organisms to overcome the constraints of ocean acidification."

University of Adelaide
Scientists Find Potential Diabetes Drug in Platypus Venom
University of Adelaide
University of Adelaide

The future of diabetes medicine may be duck-billed and web-footed. Australian researchers have found a compound in platypus venom (yes, venom) that balances blood sugar. The team published their results in the journal Scientific Reports.

So, about that venom. The platypus (Ornithorhynchus anatinus) may look placid and, frankly, kind of goofy, but come mating season, the weaponry comes out. Male platypuses competing for female attention wrestle their opponents to the ground and kick-stab them with the venom-tipped, talon-like spurs on their back legs. It’s not a pretty sight. But it is an interesting one, especially to researchers.

Animal venoms are incredible compounds with remarkable properties—and many of them make excellent medicine. Many people with diabetes are already familiar with one of them; the drug exenatide was originally found in the spit of the venomous gila monster. Exenatide works by mimicking the behavior of an insulin-producing natural compound called Glucagon-like peptide 1 (GLP-1). The fact that the lizard has both venom and insulin-making genes is not a coincidence; many animal venoms, including the gila monster’s, induce low blood sugar in their prey in order to immobilize them.

It’s a good strategy with one flaw: GLP-1 and compounds like it break down and stop working very quickly, and people who have trouble making insulin really need their drug to keep working.

With this issue in mind, Australian researchers turned their attention to our duck-billed friends. They knew that platypuses, like people, made GLP-1 in their guts, and that platypuses, like gila monsters, make venom. The real question was how these two compounds interacted within a platypus’s body.

The researchers used chemical and genetic analysis to identify the chemical compounds in the guts and spurs of platypuses and in the guts of their cousins, the echidnas.

They found something entirely new: a tougher, more resilient GLP-1, one that breaks down differently—and more slowly—than the compounds in gila monster spit. The authors say this uber-compound is the result of a "tug of war" between GLP-1’s two uses in the gut and in venom.

"This is an amazing example of how millions of years of evolution can shape molecules and optimise their function," co-lead author Frank Gutzner of the University of Adelaide said in a statement.

"These findings have the potential to inform diabetes treatment, one of our greatest health challenges, although exactly how we can convert this finding into a treatment will need to be the subject of future research."


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