June 2022
Bird of the Month
by
Ryan Crouse

Anna’s Hummingbird

The diminutive Anna’s hummingbird has carved a disproportionate chunk out of Prescott’s collective bird psyche. It’s simple; people love them! When it comes to Arizona though, this often means the magenta-throated Anna’s.

John West

The Anna’s enjoys the northernmost year-round range in North America. During the wet and body-heat-zapping winters of the Pacific Northwest, this cold-tolerant little bird will range as far north as British Columbia, and has even been recorded in the frigid expanses of Alaska.

In the Prescott area the Anna’s is the only hummingbird that we can reliably find during our cooler months. While Prescott is certainly no Anchorage, overnight lows into the negatives are not unheard-of. These temperatures would test the limits of most human life left exposed to the elements, so how does one of the smallest warm-blooded creatures on Earth survive the bitter nights? The simple answer could be that they’re just tougher than us, and while that’s definitely true, there is a scientific explanation.

In the same way a bear will spend the winter months in hibernation, an Anna’s hummingbird will mimic this process, but only to get through a single night or perhaps the occasional northern Arizona tempest. We know this survival technique a “torpor state.” During torpor, the bird can lower its body temperature from 104°F to just below 50°F.

An average human would have lost consciousness about 3°5 before that and may have succumbed to death at about 20° warmer. The bird’s metabolic rate falls to about 1/300th that than when in flight, and respirations per minute drop to approximately 2.5% of the normal rate. In short, they’re in a state near death, so much so that we have personally heard of people retrieving Anna’s hummingbird “corpses” on the morning after a cold snap and discarding them accordingly. This is often followed by a phone call to our shop, where they report the sad discovery and ask in bewilderment why the bird didn’t have the good sense to find a warmer climate.

Our honest answer, that they likely threw away or flushed a living bird, is always an unfortunate one. In almost any circumstances, human intervention in natural processes is not a good thing. With exposure to the morning’s relative warmth the bird will generally wake from its torpor over a 20-minute period, and go about its day.

Another unique trait of the Anna’s is a migration style based more on elevation than latitude. Where a Rufous hummingbird can winter into the southernmost jungles of Mexico and breed as far north as southern Alaska, the Anna's lives year-round along the Pacific coast and into Arizona. They will venture east into the intermountain West during the summer, expanding their range to take advantage of the abundant food base.

In Prescott we are positioned perfectly to experience this annual routine. The Anna’s wintering grounds in Arizona generally extend to the northern border of the Sonoran Desert. While they can survive the cold, only a small percentage of Prescott’s population stays through the winter.

While most yards won’t host these birds, we do get consistent reports of Anna’s sightings, mostly on southern or eastern slopes for maximum winter daylight. This exposure allows for a longer growing and flowering season while also encouraging more insect activity, creating more reliable food sources for the Anna’s, which can comsume half its weight in flower nectar daily. Rich in sugar, nectar is the backbone of their diet, serving as high-octane fuel for their elevated metabolic output.

With energy consumption roughly 80 times that of a human by weight, food intake is of utmost importance. To help keep up their ever-depleting energy and provide other nutrients, they will hawk and glean foliage for insects, arachnids and their eggs. During the bleakest periods of food supply they will seek out the sap-wells of sapsuckers, where they can find sucrose-dense pine and oak pitch, along with the bugs trapped in it.

Beyond the ubiquitous backyard hummingbird feeder, another great choice is to plant and maintain a native flowering garden. Some readily available, beautiful and drought-tolerant options include penstemon, manzanita and a range of flowering cacti. While they’re tough little birds, the more habitat we can help provide, the better off we all are.

Till next time, happy birding!

The Prescott Audubon Society is an official chapter of the National Audubon Society. Check it out online at PrescottAudubon.org.