(Click here to listen to a audio version of this blog!)
Here in Western Pennsylvania, no matter how much we might want them, there are no hummingbirds in our yards and gardens during our winter months. Our hummingbirds left back in September or early October and flew south to Mexico and Central America where they are now feasting on insects, spiders and plant nectar in warm, tropical luxury. Their fall migration is hardwired into their genes and is absolutely essential for their survival. They could not find sufficient food in our cold, snowy winter ecosystems. Shortening day length triggers physiological changes that causes these tiny birds to accumulate fat that will help to power their long flight south. The changes in day lengths also alter the hummingbirds’ behavior making them increasingly restless. Eventually, they reject the full nectar feeders and the flower beds that they had so vigorously fought over all summer and give into an overwhelming urge to fly south.
I have written about our Western Pennsylvania hummingbirds before (see “Hummingbirds”(July 7, 2012) and “Hummingbird Migration”(September 5, 2013)). They are a lively part of our summers. Their departure is an important Sign of Fall and their return is a glorious Sign of Summer! Imagine how surprised I was out in Seattle in November, 2012 when a robust, male hummingbird dive bombed me while I stood on the balcony of our Air B and B! The hummingbird was the non-migratory “Anna’s hummingbird” (Calypte anna), and its story is a very neat example of the impacts humans can have on the ecology and evolution of another species.
Anna’s hummingbird’s natural range was the relatively small area of extreme southern California and the northern-most parts of Baja California. In this compact area the birds consumed a wide variety of types of insects and arachnids and drank nectar from a diverse group of flowering plants. They also drank tree sap (especially from trees whose bark had been fractured by feeding woodpeckers or sapsuckers) and readily ate any insects that might have gotten caught in the sticky secretions. Anna’s hummingbird was by necessity an extreme generalist with regard to their dietary preferences because no one plant or insect was present in sufficient abundance to support their entire population, and for similar reasons they were not terribly picky about where they built their nests. The desert to the east and the dry chaparral to the north very effectively restricted their dispersion out from their natural range. Humans, though, eventually changed the vegetational map of both the west coast and the southwest desert and freed Anna’s hummingbird from its ecological confinement.
As people moved into California they planted more and more nectar producing, often exotic, plant species in their yards, parks and gardens. They also planted large numbers of exotic trees which were sources not only of insects but also nectar and tree sap. One type of tree around which large numbers of Anna’s hummingbird are regularly found is the eucalyptus, and eucalyptus trees were extensively planted in California starting in the mid-1800’s. By the early 1900’s, Anna’s hummingbird had spread out from its restricted habitat range. Its ability to consume so many different types of plant nectars and insects and its broad tolerance of nesting sites allowed it to establish itself in almost any human modified habitat that it encountered.
Anna’s hummingbird spread north up the coast of California and now is found in abundance up to Vancouver, Canada (with occasional birds found even further north all the way up into Alaska!). To get an historical time perspective on the rate of this spread, Anna’s was first recorded in the Puget Sound area around Seattle in 1964. Anna’s eastward movement through the desert (from one human manufactured oasis to the next) now stretches across Arizona and New Mexico into the western-most reaches of Texas and up into southern Nevada and Utah. Because of their ability to utilize the human constructed, exotic species dominated plant communities of yards and parks, there are many more Anna’s hummingbirds today than there were prior to European colonization of the west coast!
My son and his partner bought a house this summer on the northern edge of Seattle’s city limits. Their yard is a lush garden of flowering plants and shrubs, succulents, and tall evergreen and deciduous trees including many fruit-bearing trees. All summer, the blooming flowers in the yard drew in significant numbers of hummingbirds, and in the fall, Joe and Marlee hung nectar feeders outside their front window and began to draw in even more.
There are two species of hummingbirds that are resident in the Seattle area: Anna’s hummingbird and the rufous hummingbird (Selasphorus rufus). Anna’s is larger (almost four inches long compared to the just under or just over three inch length of the rufous), and the Anna’s males are distinctively marked with metallic green backs, heads and sides and bright red throats and crowns. The female Anna’s also have green backs but with much more subdued gray bellies. The female Anna’s, though, unusually for female hummingbirds, may also have some spots of red on their throats. The male rufous hummingbird glows bright orange in the full sunlight and has an iridescent red throat. The rufous females are more muted in color with green backs and heads and rust colored sides. The immatures of both Anna’s and rufous resemble the females in plumage.
The rufous hummingbird, unlike Anna’s, is migratory. It leaves its northern breeding regions in the fall and flies to the southwestern rim of the United States and northern Mexico to overwinter. Migration in this species, like our ruby-throated hummingbird here in Pennsylvania, is obligatory. So as winter comes on, the only hummingbirds visiting the nectar feeders in Seattle will be Anna’s, but the mix of adult males, adult females and immatures may make the flock of hummingbirds seem diverse even though it is a monospecific assemblage. A flock of hummingbirds, by the way, can be called a bouquet, or a glimmer, or a glittering, or a shimmer!
The Pacific Northwest in spite of its high latitude is kept relatively warm in the winter by the proximity of the Pacific Ocean. There are some days, though, and many nights when temperatures drop below freezing and when snow may actually fall on coastal locations. Anna’s hummingbird is able to tolerate these extreme conditions by utilizing two physiological adaptations: 1. It can quickly convert the sucrose that consumes during the day into fat (which then serves as both a body insulator and also an efficient metabolic fuel for the long, cold night), and 2. It can go into a low metabolic rate torpor at night to conserve energy.
Humans can reduce the metabolic stress on Anna’s hummingbird by planting winter blooming plants in their yards (plants like winter jasmine, winter blooming grapes or witch hazel), or by maintaining outside nectar feeders throughout the winter. Keeping the nectar bottle from freezing is vital and the Seattle Audubon Society recommends using either plumber’s heat tape, a hanging, shop “trouble” light, or even a coiled up mass of outdoor Christmas lights to keep the nectar above freezing. Duct taping a hand-warmer packet to the side of the feeders is also a good short-term heat fix against nectar freezing! Taking the feeders in each evening is also a possibility, but you have to remember that hummingbirds get up VERY early in the morning! The Seattle Audubon also stresses that the nectar should only be made with cane sugar (sucrose) and only be mixed in a one part sugar to four parts water ratio. Higher sugar concentrations may actually make it hard for the hummingbird to suck the sugar water up across their tongues and may even do damage to the bird’s kidneys and liver.
There are so many wonderful things about the Pacific Northwest! The mountains, the rocky ocean shores, the vast forests, the hiking, the food, the craft beers and the coffee! It seems unfair that they get to have winter hummingbirds, too!