Male Anna’s Hummingbird - Photo: Bob Boekelheide
Anna's vs Rufous Hummingbirds
by Bob Boekelheide
May 2021
In place of the former Bird Sightings column, Bob is exploring data from OPAS Community-Science Projects. If you are interested in local bird sightings, check out eBird at https://ebird.org/explore, then under "Explore Regions" enter Clallam or Jefferson County. Please join eBird and add your own sightings, as well.
One of the biggest changes to the avifauna of the Pacific Northwest during the last 50 years is the phenomenal increase of Anna's Hummingbirds. In a tiny eye-blink of time, these pugnacious little birds have skyrocketed from nonexistence to become one of the most abundant backyard birds in our area.
Male Anna’s Hummingbird - Photo: Bob Boekelheide
There is no doubt that Anna's Hummingbird numbers have exploded, as shown very well by the Sequim-Dungeness Christmas Bird Count (SDCBC), held each year in mid-December (see Figure 1). When the SDCBC started in 1975, Anna's Hummingbirds were considered a rare bird in western WA, and the very first Anna's did not occur on the SDCBC until 1994. From 1994 to 2005, Anna's were still very hard to find, with only one to three recorded each CBC. The Anna's count surpassed 10 for the first time in 2006, then blew through 100 by 2013. The number continues to climb, setting new records every year for the last five years, reaching 340 in 2020. Cities such as Victoria BC now record over 1000 Anna's on their CBCs.
How could this little hummingbird move north so quickly? Some people credit climate change, thinking that warming climate has allowed this species to move north in just a few years. Climate change may influence some of their recent movements, but a close look at the records shows that Anna's Hummingbirds have been moving north for almost a century.
In Birds of America, one of the early classics of popular ornithology published in 1917, William Finley describes Anna's Hummingbird as "quite restricted in its range, living through central and southern California mainly west of the Sierra Nevadas." But by 1944, in their landmark book "The Distribution of the Birds of California," Joseph Grinnell and Alden Miller describe a different scenario: "Because of human settlement of open valleys and plains and the clearing of woodland, with extensive gardening and the planting of flowering, non-native trees, the numbers of Anna Hummingbirds now no doubt greatly exceed those comprised in original aggregate population. An important factor is the presence now of plants which flower abundantly all through the quiescent period for the most native kinds of shrubs, roughly, October to January. This means that the rigors of a minimum food period in the annual cycle have been abated..."
My major professor in college, Miklos Udvardy, liked to tell the story about Anna's Hummingbirds spreading into northern California with the planting of eucalyptus and acacia trees. As Udvardy explained, these trees bloom in the winter, providing a nectar source for year-round Anna's Hummers. The trees are also an insect source, attracting swarms of gnats around the flowers. Even in 1917 Birds of America says "One may often find this hummingbird nesting in the eucalyptus."
Female Anna’s Hummingbird on nest - Photo: Dow Lambert
There aren't many eucalyptus trees around western WA, so what allows Anna's Hummingbirds to stay here all winter? One contributing factor is backyard hummingbird feeders. The appearance of hummingbirds and hummingbird feeders goes hand-in-hand. Previously we took down our feeders after the last Rufous Hummer migrated away in late summer, but now we keep the feeders up year-round, giving resident Anna's Hummingbirds a ready food source. Many of us even accommodate Anna's by heating our feeders when temperatures drop below freezing.
It is no coincidence that the highest numbers of Anna's Hummingbirds observed on Pacific Northwest CBCs occur in the largest cities like Seattle, Vancouver, and Victoria, where hummingbird feeders also concentrate. In 2017, Vancouver, B.C. even voted Anna's Hummingbird their official "City Bird," beating out quintessential Northwest species like Varied Thrush and Spotted Towhee. Ironically, Anna's Hummingbird was a very rare bird in Vancouver B.C. only 40 years ago, as shown by their CBC data.
One twist to this story is that some male Anna's Hummingbirds sit on their territories all winter, far from the nearest feeders even on the coldest days with ice and snow. This is true at RR Bridge Park, where our Wednesday morning bird walks record Anna's males perched on their territories when there is snow on the ground and temperatures in the teens and 20s. Curiously, Anna's have been recorded flying over a kilometer to reach feeders, so is that how the RR Bridge Park birds survive cold snaps? Anna's Hummingbirds are also well known for entering torpor when temperatures drop at night, by allowing their body temperatures and heart rate to drop precipitously. Clearly they have the physiological means to survive cold temperatures as long as they can find food.
If they're not drinking nectar, what do they eat? Anna's Hummingbirds likely have the highest proportion of insects and spiders in their diet compared with other hummingbirds. Even during winter we see insects in RR Bridge Park, particularly swarms of gnats. There are also spiders, which the hummers pick out of webs. I'm sure the hummingbirds are far better at finding insects and spiders than we are, so if we see them, the hummingbirds undoubtedly do, too.
Another question is how do Anna's and Rufous Hummingbirds relate to one another? Do they compete for food and territories? As Anna's increase in abundance, what has happened to the numbers of Rufous Hummingbirds?
First, the annual cycle of these two hummingbird species could not be more different. Around here, Anna's Hummingbirds appear to be year-round residents, although evidence suggests that they disperse during their non-breeding season. The Anna's Hummingbird we see at RR Bridge Park in the summer may not be the same Anna's Hummingbird we see at RR Bridge Park in the winter. Anna's also nest very early, even laying their first eggs during winter.
Rufous Hummingbirds, in contrast, are the most migratory of all hummingbird species, migrating as far north as Alaska during the nesting season and as far south as southern Mexico and the US Gulf Coast for winter. In Sequim, the first Rufous males appear on territories in early March and are mostly gone by the end of June. Most females arrive later in March and the last females and young migrate away by the end of July. After nesting, Rufous Hummingbirds may even fly inland to the Rocky Mountains to get nectar from mountain wildflowers. This means that Rufous are here for only four months or so each year. Do Anna's have an advantage simply because they are here all year?
Male Rufous Hummingbird - Photo: Dow Lambert
The only local data we have for changes in the relative abundance of the two hummingbird species comes from our community-science Wednesday morning bird walks at RR Bridge Park, which celebrate their 20-year anniversary this coming September. Figure 2 uses bird walk data to show the average numbers of the two hummingbird species counted per walk during the three-month period (April to June) in which Rufous Hummers are present each year, for the years 2007 to 2020. In Figure 2, Anna's are represented by green symbols and Rufous are the red symbols.
Figure 2 reveals amazing changes in the abundance of these two hummingbird species over the last 15 years. First off, Anna's Hummingbirds did not regularly occur in RR Bridge Park until 2008. From 2008 to 2011, Rufous clearly outnumbered Anna's, averaging 6 to 8 Rufous per walk compared to less than two Anna's. From 2012 to 2017 the two species tracked fairly close, although Rufous still held the edge. From 2018 to 2020, Anna's easily surpassed Rufous, climbing in 2020 to an average of over eight Anna's seen per walk compared to less than three Rufous.
The regression lines for each species in Figure 2 tell an ominous tale. The slope of the green Anna's line shows an increase on our walks of about 0.5 birds per year, whereas the slope of the red Rufous line shows a decrease of about 0.3 birds per year. Does this mean that Rufous Hummingbirds are being pushed out by the Anna's?
Maybe, maybe not. These data just look at disturbed habitats in RR Bridge Park that may favor Anna's over Rufous. Rufous Hummingbirds are still more abundant in many surrounding habitats, particularly away from human habitation such as in the foothills and the Olympic Mountains. Some people believe that Rufous are the more aggressive species at feeders compared to Anna's, but, despite that, Rufous appear to be declining in the lowlands where feeders are located, perhaps because of the pervasive presence of Anna's. A better question might be: What is happening to the Rufous Hummingbirds?
Finally, let's return to the other question about whether Anna's Hummingbirds are increasing in the Pacific Northwest due to climate change. Anna's Hummingbirds are unquestionably increasing in the northern part of their range, but does that mean they are simultaneously declining at the southern part of their range, like in Southern California, with its drought, fires, and unrelenting heat? It turns out that Anna's are still abundant in Southern California as shown by CBC data, likely attracted to feeders just like here in the Pacific Northwest. Whether they are equally abundant in their native chapparal habitat is uncertain. Regardless, it suggests that their increase on the north Olympic Peninsula is just as likely because of cooperative humans like OPAS members who provide year-round sugar water as it is to climate change. It will be most interesting to see what happens over the next 50 years.
Excuse me while I go fill my hummingbird feeder.