Birds

Hummingbirds enter overnight hibernation-like state to save energy for long trip south: U of T research

Christopher.Sorensen — Wed, 15 Dec 2021 15:41:12 +0000

Hummingbirds enter overnight hibernation-like state to save energy for long trip south: U of T research

Christopher.Sorensen Wed, 12/15/2021 - 10:41

Alexa Battler

Topic

Breaking Research

Birds

Biology

Graduate Students

Research & Innovation

U of T Scarborough

Hummingbirds’ metabolisms are so fast that they face an ever-looming threat: running out of energy and dropping dead. That’s why the birds evolved a physiological trick, an ability at the centre of a new study by researchers at the ��Ƶ Scarborough’s Welch Lab and Western University.

It’s called torpor – a state similar to hibernation, in which a hummingbird's body temperature drops 20 degrees or more and their metabolic rate slows by up to 95 per cent. The researchers suggest hummingbirds use this ability strategically.

“They're basically shutting off at night and then just waking up in the morning like they arose from the dead,” says Erich Eberts, a PhD candidate at U of T Scarborough and lead author of the study into torpor and hummingbirds. The paper was published this month in the journal ELife.

Eberts spent three years trying to determine the rules of torpor – that is, when and how much energy a hummingbird has when it goes into that state. He was shocked at how clear the numbers were.

“I wondered if he would observe enough instances of torpor to tell what the patterns were,” says Kenneth Welch, associate professor in the department of biological sciences. “About halfway through that first summer, he was getting birds going into torpor almost every night. But not long after, he said, ‘The birds are suddenly doing something very different.’”

Like hibernation, torpor involves severely lowering metabolism and temperature. Unlike hibernation, torpor is short-term (photo courtest of Erich Eberts)

In fact, torpor in hummingbirds does appear to follow rules – seasonal ones. In early and mid-summer, when male hummingbirds stay light and agile to defend their turf and court mates, they use torpor to survive so-called “energy emergencies.” The researchers’ study determined this emergency state kicks in when their fat levels drop below five per cent of their body mass.

“These data help simplify this almost nebulous question of when hummingbirds use torpor; it's when they hit this emergency level of fat during the night,” Eberts says. “But the really interesting part was that the five-per-cent threshold essentially disappeared in late summer right before the migration period.”

The study found that when it’s time to migrate, the birds will enter torpor at high body-fat ratios, even up to 40 per cent. By eating more during the day and using torpor at night, the birds can better prepare for the journey south. Researchers have previously observed hummingbirds fattening up before migration, but whether it was due to torpor was unconfirmed.

“Hummingbirds can use torpor in different contexts to support their seasonal energy demands. It's this really versatile energy manipulation mechanism,” Eberts says. “We were also able to show that they can fatten up more if they use the torpor more.”

Eberts studied 16 male ruby-throated hummingbirds (female birds only rarely enter torpor during nesting to keep chicks warm) in the vivarium at the Advanced Facility for Avian Research at Western University with co-author Chris Guglielmo, a professor in Western's department of biology. Before the birds went to sleep, he used a QMR machine, which works like an MRI that generates numbers instead of images, to measure body fat. The birds were then placed in a respirometry chamber to measure oxygen use and how quickly they used their fat. A steep drop in metabolism and body temperature indicated they were entering torpor.

The study suggests that torpor is more than an emergency fail-safe – hummingbirds can use it to meet different energy needs.

"If evolution has solved this problem of dealing with energy emergencies in different animals, then maybe we can learn about flexibility in the rules for drastically shutting down metabolism," Welch says. "From the human-centered perspective, we'd love to be able to put astronauts into torpor for, say, their journey to Mars."

Eberts is now looking into the effect temperature has on the five-per-cent fat threshold hypothesis. He’s also examining whether ages and sexes of hummingbirds impact their use of torpor.

“There's somewhat of a debate on how common torpor is in birds in general, so considering the flexibility of torpor use is important for more broadly understanding the scope of torpor use in other animals,” he says.

The study was supported by the Natural Sciences and Engineering Research Council of Canada, Human Frontier Science Program, Canada Foundation for Innovation and Ontario Research Fund.

The Versatility of Torpor-use in Ruby-throated Hummingbirds from Deniz Kaya on Vimeo.

Common agricultural pesticide may be putting hummingbirds at risk: U of T study

Christopher.Sorensen — Thu, 18 Feb 2021 18:26:32 +0000

Common agricultural pesticide may be putting hummingbirds at risk: U of T study

Christopher.Sorensen Thu, 02/18/2021 - 13:26

Cutline

Researchers at U of T Scarborough discovered that a common insecticide can slow the metabolism of ruby-throated hummingbirds by as much as 25 per cent in the hours after exposure (photo by mlharing via Getty Images)

Topic

Research & Innovation

Sustainability

U of T Scarborough

Hummingbirds need an incredible amount of energy to flap their wings 50 times per second to maintain hovering flight. Their metabolism is so supercharged that if they were human-sized they would consume energy at a rate more than 10 times that of an Olympic marathon runner.

But a new ��Ƶ study has found that a common agricultural pesticide might be slowing down the crucial physiological process that makes hummingbirds so unique.

Researchers in Associate Professor Ken Welch’s lab in the department of biology at U of T Scarborough discovered that a common insecticide – which is chemically related to the nicotine found in tobacco – can slow the metabolism of ruby-throated hummingbirds by as much as 25 per cent in the hours after exposure.

“We don’t know exactly why it goes down – whether the chemical is disrupting the metabolic processes or because they simply feel sick as a result of exposure – but they definitely show a reduced metabolic rate during the first few hours after ingesting it,” says Welch.

Neonicotinoid pesticides, introduced in the 1990s and now the most common type of insecticide in the world, are effective at killing insects because they can be transported to every part of a sprayed plant including the leaves, stems, roots, flowers, nectar and fruit. They can also persist in the soil and the plant for more than a year. However, the effects of pesticide concentrations in wild birds are just beginning to be understood.

Welch says that hummingbirds may be especially prone to the negative effects of exposure because they encounter the pesticides in a number of ways, including through spraying, eating contaminated insects and, especially, drinking the contaminated nectar of sprayed plants.

He says it’s also clear that hummingbirds are being exposed to these chemicals in the wild, pointing to recent research where the chemical was found in hummingbirds that lived near sprayed blueberry crops in B.C.’s Fraser Valley. The research, by Welch’s collaborators at Environment and Climate Change Canada, found the chemical in the nectar of blueberry plants up to a year after it was sprayed, and also in the urine samples of hummingbirds collected during the spring and summer.

It begs the question about the long-term effects of chronic exposure.

“We only looked at the first few hours after exposure, but theoretically there could be a long-term impact on the central nervous system,” says Welch, a renowned expert on hummingbirds.

He explains that the pesticide works by essentially paralyzing an insect’s ability to breathe and move through disruption of the nervous system.

“We could assume that those potential risks also exist for hummingbirds through long-term exposure. At the moment, we just don’t know. It would require more research.”

The study, published in the journal Scientific Reports, which received funding from Environment and Climate Change Canada and the Natural Sciences and Engineering Research Council of Canada (NSERC), raises important policy considerations. While all outdoor uses of several neonicotinoid pesticides were banned in Europe in 2018 to protect wild bees, they are still commonly used in North America.

At the very least, Welch says some consideration should be given to when the pesticide is sprayed, especially during periods when vertebrates or important pollinators are active to reduce the chances of exposure.

“If hummingbirds are skipping their normal foraging behaviour because of a dip in their metabolic rate, it could put them in an energy bottleneck,” he says.

“If they’re already low on energy, and then they are exposed to this pesticide, that hummingbird may very well find itself in an energetic crisis not too long after.”