The desiccated crunch of dead leaves underfoot. A gloomy night’s chill prickling your skin. When, oh, what poor little creature is this on the ground? An extinguished little jewel. A hummingbird now hushed. Lifeless but still so lovely. You set it on the porch to mourn in the morning. But when you return, there in the dim glow of dawn, somehow whirring wings, flapping feathers. A bird back from the dead! A humming-zombie?! Read on to learn about the autumnal activities of the Ruby-throated Hummingbird, with a twist fit for spooky season!

While I happily welcome autumn’s arrival, I also relish the ruby-throated relics of summer that are still sipping nectar in my backyard. I know we are quickly approaching the time that any sighting could be the last until next spring. But not only are my feeders not yet fallow, they are busier than ever with soon-to-be-migrants (or perhaps birds from more northern latitudes already on their way south) fueling and fattening up before the journey to come. This month, the last of our remaining hummingbirds will take wing for their tropical winter climes. But first our busy little birds are feasting!

Exactly when our hummingbirds decide to depart is probably a complicated interplay of the birds’ own instinctual hardwiring and environmental factors like declining daylight hours, cooler temperatures, and decreasing natural food sources, all of which trigger hormonal signals that let the Ruby-throats know it’s time to stockpile a tremendous amount of energy for their flight to their wintering grounds. Interested in learning what hummingbird biology can teach us about human disorders, scientists at Johns Hopkins Medicine have studied the Ruby-throated Hummingbird’s extraordinary metabolism, which is over 77 times faster than a human’s:

“To keep up the blistering pace of their flight, they need the human equivalent of over 150,000 calories every day. To survive their migration, the birds rapidly pack on weight, as much as doubling it in a matter of days. They slurp down so much sugar that their blood sugar levels are high enough to kill or seriously hurt a human. Much of the sugar goes straight to their muscles to fuel the constant buzz of their wings and their rapid heartbeat, which can reach up to 1,200 beats per minute. Other sugars wind up in the liver where supercharged enzymes process them into fat that fuels the birds’ migration.”

So it’s no wonder our fall feeders are particularly popular when convenient calories are needed most. While we know of hummingbirds’ intense need for nectar, they do require protein from insects as well. Victorians attempting to keep captive hummingbirds were the first to discover that birds fed exclusively sugar syrup would not live as long as birds kept in rooms with open windows that allowed insects to fly inside. We now know insects account for upwards of 60 percent of a hummingbird’s diet! They can catch insects midair, or pluck spiders from their webs. So in addition to keeping nectar feeders and native flowers available, fostering an insect-friendly habitat will also help attract more hungry hummingbirds to your yard.  

In order to retain the stores of body fat they’re building before migration, the Ruby-throats not only consume more, but expend less. They, like many hummingbirds and other animals, can enter a hibernation-like state called torpor to conserve energy. Their body temperature can dip by as much as 20 degrees and their heart rate can drop from 200 beats per minute even at rest to less than 50 beats in torpor, which allows their metabolic rate to decrease as much as 95 percent. A recent study discovered that Ruby-throats appear to use torpor strategically and seasonally. Nesting females rarely deploy torpor when they need their own body heat to keep chicks warm. But in summer, males may enter torpor to survive short term “energy emergencies” when their body fat dips below five percent. As they ready for migration, however, Ruby-throats will enter torpor even when their body fat is as high as 40 percent. The authors found, “[T]he more time birds spent in torpor, the more fat they gained. This suggests that in late summer, hummingbirds switch from using torpor as a survival strategy to using it to maximize energy savings before migration.”

Should you ever find a hummingbird you believe might be distressed or dead, it is best to proceed cautiously and observe first. Wild Birds Unlimited offers this helpful advice: “Hummingbirds in torpor may look and seem to be dead, clinging tightly with their feet locked around a small branch, eyes closed, and beak often pointing skyward. They will feel cold, lifeless and are unresponsive to touch. Then, shortly before dawn they begin to waken by shivering to warm the muscles, complete revival usually taking about an hour. People have found hummingbirds in torpor and thinking that they were dead, occasionally have put ‘dead’ hummingbirds in a trash bin only to hear them fluttering around inside trying to escape an hour or so later. If you find a hummingbird in this condition it is best to leave it alone; it may simply be in torpor and will have a normal recovery to daytime activities.” 

So by the time us human creatures are ready for our annual sugary celebration at the end of the month, most, if not all, of our ruby-throated residents will have departed, having already filled themselves with their own sweets and treats to fuel their fall voyage south. Until then, I will enjoy the last few remaining glimpses of ravenous little Ruby-throats visiting my feeder. Please revisit our January article to learn more about their fall migration, and a reminder that although our Ruby-throats have left us, our winters here in North Carolina are not necessarily hummingbird-less! 

Blog post written by Brittany Richards