It’s Spring Madness out there as Sonoma County’s songbirds swoop into the full-court press of their breeding season. Bird song and other breeding behavior is as astonishingly complex as it is beautiful to behold. Fortunately, one need not be an ornithologist or even an amateur birder to appreciate this annual avian spectacle. Becoming familiar with just a few of our local feathered friends makes any outdoor adventure that much more meaningful and even mind-blowing.
Two birds that are easy to recognize, fun to watch, and fairly ubiquitous in our local parks and open space areas right now are western bluebirds (Sialia mexicana) and tree swallows (Tachycineta bicolor).
Another closely-related swallow — the brilliantly colored violet-green swallow (Tachycineta thalassina) — is less commonly seen, in part because it flies so fast and so high, although if you do get a good look, it will take your breath away.
All three are cavity-nesters that share similar habitat, and all have adapted readily to human-provided nest boxes. As a result, we actually know quite a bit about their private lives and how they interact with each other.
Few common birds have as devoted a human following as bluebirds. Perhaps it is their ability to stop you in your tracks with a flash of brilliant blue wing. Perhaps it is their generally chill demeanor combined with an easy-to-watch habit of perching relatively low and swooping to the ground to snag an insect. I suspect their popularity is at least in part due to the fact that people have learned to help these birds survive through the deployment and monitoring of nest boxes. Conservation success stories this intimate are hard to come by and here is one in which we can all participate, literally in our own backyards.
The western bluebird is found throughout the American west and in our area is a year-round resident. During the winter months in our oak woodlands, bluebirds can be found hunkered down in clumps of oak mistletoe, munching on its sugar-rich berries. So important is this seasonal resource, whole families of western bluebirds will claim and defend a mistletoe patch. In her acclaimed 2014 book “Secrets of the Oak Woodlands” (Heyday, $18), local author and naturalist Kate Marianchild explains that mistletoe even determines family structure of bluebirds in the wintertime. Researchers found that when mistletoe clumps were removed from an area, the male offspring in the family left the area.
Bluebirds are considered “socially monogamous,” which means they form strong long-term pair bonds, which may last their entire lives. However, these pair bonds are somewhat fluid — up to 25 percent of bluebird young in a given nest have a different daddy. Nevertheless, family life among bluebirds is relatively stable and cooperative. At the end of summer, female offspring will move in with another family while new “daughters-in-law” move in with her birth family. While most songbirds drive off their young as soon as they can forage for themselves, bluebird parents keep their sons and daughters-in-law around, even though that means more competition for food. It turns out that some of these hangers-on — especially the sons and brothers from the previous year — help the breeding pair raise their young. Indeed, sometimes breeding bluebird pairs will raise their own family while at the same time helping to feed and defend the offspring of their relatives. Ultimately, bluebirds who cooperate end up having more young and living longer than those who go it alone.