Birds
Ruby-Throated Hummingbird
Archilochus colubris · also called common eastern hummingbird
The ruby-throated hummingbird is the most familiar hummingbird in eastern North America and a study in living at the physical limits. It is one of the smallest birds on the continent, it has the fastest metabolism of any warm-blooded animal its size, and it makes one of the most improbable migrations in the bird world.
Overview
Ruby-throated hummingbirds breed across the whole eastern half of North America, in woodland edges, gardens, parks, and clearings with flowers. They are the only hummingbird that nests east of the Great Plains. In autumn nearly the entire population funnels south to Mexico and Central America, and returns the following spring, timing the journey to the flowering of particular plants along the route.
Extreme physiology
A hummingbird’s body is organised entirely around powering flight:
- A huge heart and flight muscles. The heart makes up a large share of body weight and beats up to 1,200 times a minute; the flight muscles are proportionally the largest of any bird.
- Constant refuelling. The bird feeds every 10 to 15 minutes all day, consuming roughly its own body weight in nectar, and would starve within a couple of hours of not eating.
- Overnight torpor. To survive the night it shuts its metabolism down, letting body temperature fall close to the air temperature.
- Unique flight. A rotating shoulder joint lets the wing generate lift on both strokes, so the bird can hover, reverse, and fly briefly upside down.
The gulf crossing
Before migrating, a ruby-throated hummingbird gorges and lays down fat until it weighs nearly twice its normal 3 grams. Many then launch out over the Gulf of Mexico and fly around 800 km without stopping, an 18-to-22-hour effort over water with no food and no rest, landing on the far shore lean and exhausted. It does this southbound in autumn and northbound in spring.
Diet and pollination
Nectar and sap fuel the bird; small insects and spiders supply everything else. In feeding, the hummingbird laps nectar with a long, forked, brush-tipped tongue that flicks in and out around 15 times a second, and it carries pollen between flowers on its head and bill — making it an important pollinator of many red and orange tubular flowers that are shaped to fit it.
Reproduction
Males display with pendulum-like dive flights, arcing back and forth in front of a female with a whirring buzz, their throat feathers flashing iridescent red. The female alone builds a walnut-sized nest of plant down bound with spider silk, camouflaged with lichen, and stretchy enough to expand as the chicks grow. She lays two pea-sized eggs, incubates them for about two weeks, and raises the young without help from the male.
Conservation
The ruby-throated hummingbird is listed as Least Concern, and surveys suggest its numbers have risen over the past several decades, helped by the popularity of nectar feeders and hummingbird gardens. The main risks are the loss of stopover habitat along the migration route and the wider decline of the insects it needs for protein.
Ruby-Throated Hummingbird: common questions
How fast do hummingbird wings beat?
A ruby-throated hummingbird beats its wings around 50 times a second in ordinary flight — fast enough to produce the humming sound the birds are named for and to blur into near-invisibility. During the males' courtship display dives the rate can exceed 200 beats per second. The wing moves in a figure-eight, generating lift on both the forward and backward stroke, which is what lets hummingbirds hover in place and fly backwards.
How does such a tiny bird cross the Gulf of Mexico?
In the weeks before migration a ruby-throated hummingbird nearly doubles its body weight, storing fat as fuel. It then flies up to about 800 kilometres non-stop across the open Gulf, a journey of around 18 to 22 hours with no chance to rest or feed, arriving having burned through most of that fat. Not every bird takes the water route — some go around the coast — but many do make the direct crossing twice a year.
What is hummingbird torpor?
A hummingbird lives so close to the edge of its energy budget that it cannot survive a cold night at normal metabolic rate. To get through it, the bird enters torpor — a deep, controlled drop in body temperature and metabolism, with the heart rate falling from over a thousand beats a minute to around fifty and breathing nearly stopping. In the morning it takes 20 minutes or more to warm back up and become active, sometimes shivering to speed the process.
What do hummingbirds actually eat?
Both nectar and insects. Sugar from flower nectar and tree sap provides the enormous amount of energy flight demands, and a hummingbird visits hundreds to over a thousand flowers a day, transferring pollen as it goes. But nectar has almost no protein, fat, vitamins, or minerals, so hummingbirds also catch large numbers of small insects and spiders — snatched from the air, plucked from leaves, or stolen from spider webs — especially when feeding nestlings.