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The Spectacular Biology of Hummingbirds with Peter Mangold D.V.M.

Summertime at Roger’s Gardens is warmly greeted by the stunning displays of our local pollinators. Monarchs float through the air, bees hum in the low shrubbery, and birds chirp gleefully from high branches. But our most daring resident isn’t so easy to observe. Blink – and you might miss it. These creatures flit through the sky at record speeds and maneuver through the gardens with rapid athleticism. A flash of a ruby throat, a whir of tiny jeweled wings, a dark, bobbing beak through a flurry of flowers. Wander the gardens long enough and you’re sure to see one perch before you, a brief pause, a breath, look! A hummingbird!

Hummingbirds are one of the most impressive creatures in the animal kingdom, paragons of tenacity and athleticism packaged neatly in a tiny feathered body. Their unique physiology allows them to carry out their impressive modes of flight, and they sustain all of this activity as nectarivores (animals who mainly consume nectar). They play a critical role in the environment as pollinators, as the pollen that collects on their beaks and feathers as they feed is carried to neighboring flowers resulting in cross-pollination, helping our crops, gardens, and natural spaces to flourish. As we gear up for a warm summer filled with the acrobatic displays of our local hummingbirds, we sought to learn more about the impressive biology of these animals. To better understand the way hummingbirds live and move, we turned to Dr. Peter Mangold, a veterinarian located in the Bay Area who studied hummingbird physiology and locomotion for his graduate research.

Dr. Mangold studied Anna’s Hummingbird of San Diego, working with a colony of about 15 birds maintained by his research lab. He sought to understand how these birds are able to achieve such impressive speeds, and more importantly, how they are able to hover, without rapid fatigue. Hovering, in fact, is the most difficult form of flight, and hummingbirds have very particular biological features in order to carry out this unique mode of locomotion. Our exciting discussion with Dr. Mangold follows below, where we learn a little more about the remarkable physiology of these tiny wonders.

Thank you so much for joining us today! To begin, let’s start off with some general questions about hummingbird biology to get better acquainted with the way they move.

How do hummingbirds feed and what do they feed on?

Hummingbirds hover (very metabolically expensive) to insert their long, thin beaks into a flower to get a taste of nectar (sugar). Then, they’re immediately off to the next flower. They spend a great deal of time hovering to feed on nectar.

They also eat a lot of bugs. The nectar just provides simple sugars, or carbohydrates. The bugs provide hummingbirds with protein, fat, vitamins, and minerals. They can’t live on sugar water alone. Typically, feeding on bugs is easier since they don’t have to hover to catch them. They pick them off the ground or off plants, or catch them in mid-flight. When flying forward, hummingbirds benefit from the lift generated by their wings, like other birds. When hovering, they have to rely entirely on their chest muscles pushing the air down against gravity. This is much more energetically taxing, as they must rely entirely on the force generated by the muscles, and cannot benefit from the lift birds generate during forward flight.

And exactly how fast do hummingbirds fly?

Hummingbirds can go from 0 (hovering) up to 60 mph or so. In a steep dive, they can move incredibly fast.

Not many animals are capable of hovering – how do hummingbirds accomplish this? What about their anatomy is different from other birds that makes this possible?

Hummingbirds move their wings in figure eights to hover, as where other birds move their wings up and down. This “egg beater” motion is actually the most efficient way to move the air. They can do it so fast (upwards of 200 beats per minute) and have such strong muscles (25% of their body weight is pectoral muscle) that they can hover for 30 – 40 seconds if they need too. When flying forward, they return back to flapping their wings up and down. They can go from an airplane to a helicopter, and back again, anytime they want!

Hummingbirds are also incredibly impressive at maneuvering quickly mid-flight. How do they do this?

Subtle adjustments to the wings and their small size equal amazing maneuverability. They also have very good eyesight for catching bugs and finding flowers, enabling them to quickly target where they need to fly.

And how fast do their hearts beat to maintain all of this rapid activity?

Their heart beats up to 1,200 times a minute, they can breathe 250 times a minute. For comparison, a human heart rate of 160 is concerning as it starts to put an unsustainable burden on the heart muscle. In fact, hummingbirds can use 10 times more oxygen than humans. So, pound for pound, they are 10 times better than an elite athlete when it comes to exercise physiology.

That’s incredible! Hummingbirds are certainly the Olympians of the animal kingdom. Let’s start to dive a little deeper into the research you did with hummingbirds. Why did you first start researching their physiology?

I was in graduate school, having graduated from UC San Diego with a degree in Animal Physiology. I was in a Comparative Physiology Master’s Program and was helping my Major Professor with her research on renal (kidney) function in extreme environments. She was studying marine mammal and hummingbird renal function. Marine mammals live in salt water, a difficult environment for the kidneys, and it’s well documented that hummingbirds have some of the most extreme physiology known to man, which also puts a significant burden on the kidneys.

At the time, I was also taking a cardiology class as part of my grad program. The professor of the class was researching the function of the human sweat gland during exercise. He was working with Navy Seals in San Diego as they often train in difficult environments and exercise to the extreme.

One day, we were talking after cardiology class, and he was very interested in the hummingbird work we were doing in the biology department. He wondered - how could the hummingbird hover for so long without their body becoming overwhelmed with lactic acid? Lactic acid is produced during rigorous exercise and causes the burning fatigue in our muscles when they are exerted. The production of lactic acid with maximal exertion, like a sprint, is what causes athletes to slow down or stop so the muscles can switch back over to using oxygen for energy (aerobic metabolism). Hovering is considered to be one of the most metabolically expensive activities possible, so how do hummingbirds hover so much without apparent fatigue? It was as if they were sprinting all the time. Running a marathon at sprinter speeds, all the time. The light bulb went off. We could find out, maybe. My professor had a Lactic Acid Assay he was using for his research in human exercise physiology, and we thought if we could miniaturize it, and get it to work with hummingbird blood, we could find out. This became the topic of my research.

And what was the topic of your research once you started working with these fantastic birds?

Our theory was that the Cori cycle activity in a hummingbird must be very fast. The Cori cycle is the process that recycles lactic acid back into glucose after exercise. As lactic acid is produced by anaerobic metabolism (intense exercise) in the muscles, it goes into the blood stream and is sent to the liver. The liver carries out the Cori cycle, converting lactic acid back into glucose, and sending glucose back to the muscles. There are active proteins, or enzymes, which carry out this process. Our theory was that the enzymes responsible for the Cori cycle in hummingbirds must be among the fastest ever recorded. We wanted to document that this was true and that this is what enables hummingbirds to hover for so long.

What was your experiment and what did you learn from this experiment?

Step one - miniaturize the Lactic Acid Assay. That took me a year. Hummingbirds don’t have a lot of blood. So, we needed to modify the assay to work on less than 30 microliters of blood. That’s about a drop. The original assay was designed for 3 milliliters (3,000 microliters).

Step two - design a way to exercise a hummingbird. We needed them to hover non-stop until they were unable hover anymore. Then, take 2 – 3 samples of blood over a minute or two. That turned out to be easier than we thought. A covered fish tank tipped up on one end was turned into the exercise chamber. Nowhere to go but hover and nowhere to land. When finally fatigued, the hummingbird landed in my hand and I quickly took a small blood sample. A minute later, another sample. Done.

Our preliminary tests showed, yes, hummingbirds make lactic acid. It also showed that, in hummingbirds, lactic acid levels in the blood decrease rapidly after exercise (the hummingbird liver sucked up the lactic acid almost as fast as it was being made). We discovered what we were hoping for - the Cori cycle enzymes in a hummingbird’s liver are among the fastest ever recorded. These enzymes rapidly recycle lactic acid back into glucose, preventing the hummingbirds from fatiguing significantly while hovering. That’s how they can ‘sprint a marathon’!

Fascinating! So these fast-acting enzymes enable hummingbirds to be the little superheroes we see hovering around in our backyards.

As you know, people have been increasing efforts to support native hummingbird populations, due to the beauty they bring to the garden as well as the important role they carry out as pollinators. People are often incorporating hummingbird friendly plants into their gardens or hanging nectar feeders to attract the birds. As a veterinarian, what do you recommend people use in their hummingbird feeders?

You can simply put 25% sugar water in the feeders. An easy source of sugar water is a nice treat for them. Usually, flowers just give them a tiny drop of sugar, whereas they can gulp it from a feeder. There are commercial products on the market that contain additional nutrients besides sugar that is beneficial for the hummingbirds, but the wild birds can also find their own bugs and other nutrients if you choose to prepare home-made nectar.

Additionally, be sure not to prepare or purchase nectar with any red food coloring or other artificial additives as this can be harmful to the birds.

If one is lucky enough to discover a hummingbird nest in their yard, what is the best way to ensure the mother and babies are not disturbed?

Like all birds, stay away. Observe from a distance only. Birds are afraid of us and are easily stressed by our presence, so it is best to give them as much space as possible.

What do you recommend individuals do when they find a hummingbird that appears unwell or unable to fly?

Call your local veterinarian to find out where to take the hummingbird. I am located in the Bay Area, and I like to direct people to the Lindsey Wildlife Museum in Lafayette. They have a veterinarian that treats wild animals that are found sick and injured.

Why do you think it’s important for people to help protect and support wild hummingbirds?

It’s simple - they’re cool! They’re fun to watch, and do incredibly important work for the environment. And, they have amazing physiology that, on occasion, some lowly graduate students get to study. My work with hummingbirds launched my career into Veterinary Medicine!

Hummingbirds are truly tiny marvels, inside and out. Their remarkable capabilities of flight are rooted in the most nuanced aspects of their biology, which allows their metabolism to run so quickly and efficiently that they are practically indefatigable. We hope that you enjoyed this discussion with Dr. Mangold as much as we did, as he illuminated just some of the many physiological aspects that makes the hummingbird way of life possible. This summer, we welcome you to join us, to gather, to watch, and to wonder, at the magnificent flight of the hummingbird.

Written by Melissa Martens of Roger’s Gardens, Corona del Mar, Ca