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It’s still mid February, but by some measures it’s already spring. The wildflowers are popping up—half a dozen species on the coastal bluffs at Point Reyes last week, and fetid adder’s-tongues and trilliums among the redwoods. I’ve seen reports of returning swallows in the East Bay: not just the predictably early tree swallows, but a couple of barn and cliff swallows as well. And some birds are well into their nesting seasons, the calendar be damned. 

Last month Daily Planet contributor Steven Finacom alerted me to a nesting Anna’s hummingbird in the courtyard of an office building on University Avenue. I found her as directed, on a branch of a Tibouschina bush in a well-trafficked part of the building, sitting tight on her small cup-shaped nest. January isn’t exceptionally early for an Anna’s hummer to be incubating eggs; some start in December. Along with the great horned owl, they’re among the first Bay Area birds to begin breeding. 

The female’s mate was nowhere in sight, of course. Male hummingbirds typically eschew nest construction, incubation, and child care. Hummer courtship is a brief encounter, males mating with multiple females attracted by their spectacular display flights. The males of some tropical hummers, like prairie grouse or birds of paradise, gather at display grounds called leks. But male Anna’s hummers have individual display territories, sometimes proximate to but not overlapping the nesting territories of females.  

I said “typically” because there’s always a counterexample. In 1970, a woman named Dale Peters Clyde was following the progress of an Anna’s hummingbird nest at her summer home in the Napa Valley. The female hummer disappeared—likely the victim of a predator—late in June, leaving two nestlings. After one fledgling had also left the nest, a hummer with the flashy red crown and throat of an adult male showed up and fed the remaining youngster. The interaction was interrupted by the chick’s fall to the patio below the nest, after which Clyde apparently tended it until it was able to fly away five days later. Granted, that’s just one anecdote; but along with scattered accounts involving tropical species, it suggests that male hummers are capable of parental behavior. 

It’s not unusual for a female hummer’s nesting activity to stretch from December or January into June. Multiple broods are insurance against the high mortality to which small birds are prone. Some overachieving females may build a second nest, lay their eggs and begin to incubate them while still feeding their first batch of nestlings.  

The nest is an impressive piece of avian architecture, a cup of plant down held together with spider silk. Like most Anna’s nests I’ve seen, the one on University had an outer coating of flakes of lichen; I had to wonder how far the bird had to go for them. 

A tiny bird that nests during the cold, rainy end of the year faces major thermoregulatory challenges. Hummingbirds have the highest metabolic rates among animals—12 times that of a pigeon, a hundred times that of an elephant. A hummer’s normal body temperature is around 104 to 111 F, its resting heart rate 250 beats per minute (the active rate can be 1,250). But in cold weather it can conserve energy by entering a torpid state, with heart rate dropping to 50 beats per minute and temperature to 55 F. This option isn’t available to nesting female hummers, though; they have to keep the eggs warm through the night. They manage this by an optimum combination of nest site selection, construction technique, and foraging behavior. 

In a study done 33 years ago, W. K. Smith at UCLA and S. W. Roberts and P. C. Miller at San Diego State rigged thermocouples to an Anna’s hummingbird nest in a Southern California oak tree in April to measure the nest’s microclimate, and monitored the female’s behavior at and around it. An overhanging limb provided protection from the cool night air (as would the walls of that building on University Avenue). The nest itself had been built to conserve heat, either by selecting material with low conductivity or by creating insulated air spaces in the nest walls. As the biologists measured it, the thermal conductivity of the nest material approximated that of polar bear fur. And the bird’s daily activity pattern included an intense bout of feeding from 2 to 6 p.m., to stock up energy reserves for the night’s expenditure of up to 2.5 kilocalories. All this enabled her to maintain an average nest temperature of 27.5 C (82 F) during the night. 

In addition to all the nectar she needs to power her metabolic furnace and the occasional insect, a nesting hummer has other cravings: females have been observed eating sand, mud, and campfire and barbecue ashes. The calcium in the shell of a hummingbird’s egg is likely borrowed from structural bone. Nectar feeders don’t get much calcium, so female hummers go for mineral supplements to replenish what is lost in egg-making. 

Very little that these improbable creatures do would surprise me. You’d expect hummers to live fast and die young, like shrews and other small mammals with high metabolic rates. But some hummingbirds have made it to the ripe old age of 12—a short span from the perspective of a 70-year-old albatross, but not bad for a little guy. 

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