Sleepy Hummingbirds

Sleepy Hummingbirds

| Anusha trains Kaheela to set a hummingbird trap for their research on hummingbird torpor. |

Hours after I finished grading final labs for this quarter’s Teaching Assistantship, I had my camera gear packed into the back of my little orange Honda and was speeding through the night towards the Arizona border. My friend Anusha, who normally lives in New York, was at a field station just nine hours away, and what better way to spend a weekend than photographing your friend’s PhD research on hummingbirds?

After racing across the state of Arizona past two forest fires and using the loosest possible interpretation of speed limits, I reached Highway 80 in New Mexico just after 2am and found myself in a veritable hailstorm of jackrabbits. I am not sure if these were Were-Rabbits lured out by the full moon or if this was an unannounced gathering of some sort of lagomorph death cult, but rabbits were hurling themselves in front of my car left and right, testing the limits of my very fastest reflexes. No sooner would I catch the reflection of eyes in the bushes at the roadside then a crazed rabbit would leap out and head full-speed straight for the spot on the road my car tires would be reaching in approximately eight milliseconds. I cut my speed in half and am proud to say I managed to avoid hitting any rabbits (probably at the expense of the longevity of my tires), save one that hurled itself straight into the side of my car after I had already passed by. I can’t say what happened to that one. Hopefully it was just stunned. Later on I heard researchers comparing personal record numbers of rabbits found on truck grills after night drives to the station, with numbers between eleven and fifteen, so perhaps this is just a necessary method of population control and I shouldn’t have felt so guilty.

I emerged from Hurricane Warren having avoided committing rabbit mass-murder and turned onto the narrow highway leading a few miles just back into Arizona to Southwestern Research Station in the Chiricahua Mountains. Although it was pitch-black and I couldn’t make out any features past the immediate trees illuminated by my highbeams, I could feel the presence of the looming sandstone cliffs that had blocked out the moonlight. After a few winding miles, I finally reached the researcher dorm where I had a bed waiting and fell asleep.

Southwestern Research Station

| Southwestern Research Station, Chiricahua Mountains. June 2017. |

In the morning I awoke to golden light illuminating the cliffs I could sense on my late-night drive in, even more grand than they had been in my imagination. At the field station’s cafeteria I met up with the research team, Anusha and her collaborators Don, Isabelle, and Kaheela from George Fox University.

Anusha is a PhD student studying the energy expenditure of hummingbirds. Hummingbirds have extremely high metabolisms—the highest of any vertebrate animal [1]—and have to consume two to three times their bodyweight in nectar each day in order to stay alive. This means that at night, when they are at rest and unable to feed, they have to employ energy-saving strategies to ensure that when they wake up they have enough energy reserves to resume the nectar hunt.


| Black-chinned hummingbird in the Chiricahua Mountains, 2017. |

To save energy and survive the night, hummingbirds enter a state of deep torpor, where a hummingbird drops its body temperature as the ambient temperature falls until it reaches some species-specific lower limit. Hummingbirds have been observed to lower their body temperatures by 26°C or more at night [2]. (In comparison, humans will become hypothermic with just a 2°C drop in body temperature!) However, the state of deep torpor takes the hummingbird a long time to wake up from, leaving the bird vulnerable to predators.

Anusha was studying whether hummingbirds enter shallow torpor, a state of inactivity where the hummingbird’s body temperature only drops by a few degrees, conserving energy but not fully entering the deep torpor state. In order to investigate this hypothesis, she was using infrared cameras and a system for measuring nighttime respiration, both of which give information about the hummingbirds’ metabolic activity.

Trapping Hummingbird

| Anusha expertly catches a blue-throated hummingbird caught in the researchers' trap. |

Southern Arizona has more than a dozen species of hummingbirds, many of which are found in abundance at the Southwestern Research Station. Black-chinned, blue-throated, and magnificent hummingbirds abound at the bird feeders and along the streams flowing a short walk from the research station grounds.

Each day of fieldwork, during the daytime, the research team set out to trap the hummingbirds to be used for long the night of measurements ahead. Trapping hummingbirds requires two things—a trap, and a lot of patience. The research team set two traps in close proximity to each other in a tree-covered clearing across a river from the research station. The traps consisted of two main pieces—the bottom a circular piece of netting, and the top a cylinder of netting that can be raised to allow the hummingbird in and dropped to trap the hummingbird safely in the net. The researchers hung hummingbird feeders full of nectar in the center of the traps, which lure in the hummingbirds to feed. A researcher sits a safe distance from the trap, holding a long string that drops the netting when released. Since the hummingbirds can move significantly faster than human reflexes, they ideally wait until the hummingbird has settled on the feeder to take a long drink, otherwise the hummingbird could flit out of the trap before the net falls.

Only the male hummingbirds are used for the nighttime experiments, since capturing a female hummer could mean that you’ve removed a mother from her hungry chicks, who need constant feeding and protection. If a female is accidentally caught, the researchers carefully catch her, give her a long drink of nectar from the feeder to replenish the energy she used up in the trap, and release her back into the wild.

Hummingbird Experimental Setup

| Anusha and Isabelle set up the infrared camera experiment by lining the hummingbird's box with plastic to cut out extraneous infrared from the background. |

Once the hummers are trapped, it’s back to the lab to set up the experiments that will occupy the researchers for the entire night. The hummingbirds are weighed and measured, and the two main experiments are set up.

The first experiment involved collecting measurements throughout the night of the hummingbird’s body temperature using a FLIR infrared camera. These measurements can be used to determine if the hummingbird has entered a state of deep torpor, or if the hummingbird enters the hypothesized shallow torpor state.

Infrared Hummingbird

| A hummingbird imaged by an infrared camera to determine its body temperature. |

The second experiment involved measuring the hummingbird’s metabolic rate by measuring its respiration, a process known as respirometry. Using a complicated-looking setup of tubes and sensors, the carbon dioxide production and oxygen consumption of the hummingbird is measured precisely to track its metabolic rate over time, in order to determine whether the bird is awake or in a level of torpor.

Respirometry Experiment

| Kaheela monitors the respirometry experiment. |

Throughout the night, the researchers stayed awake to monitor the two experiments, sleeping in shifts to ensure the night’s data is complete. I never fail to be inspired by the dedication and sacrifice scientists around the world demonstrate in their pursuit of knowledge and understanding.

Feeding Hummingbird

| Isabelle feeds a Blue-throated Mountain-gem hummingbird in preparation for its release. |

In the morning, when they have awakened from their torpor, the hummingbirds are fed a generous breakfast of sugar water and released out into the morning sun. The researchers, exhausted from a night of very little sleep, grab a nap (or a big cup of coffee) and make preparations to catch more hummers for the next night’s round of data.

Sadly, after only a few days of enjoying the routine of research and observing the secret lives of scientists and hummers, I had to leave the fun behind and drive back to San Diego to catch an early-morning flight to D.C. for the annual National Geographic Explorers Festival. The researchers stayed, continuing the tireless task of data collection for several more weeks.

And the most exciting part? Anusha’s work from this field season and prior ones found evidence for the existence of a shallow torpor state in hummingbirds! [3] An exciting conclusion to a cool hypothesis about these fascinating little birds.