Mountain Bluebirds are the sky-blue members of the bluebird family (especially if your sky is the sun-drenched firmament of Colorado). CO is the winner in the MOBL competition, with 12% of the US population, followed closely by New Mexico and Wyoming (both at 10%) then Montana, Oregon, and Utah (all at ~9%). In CO, they breed in pinyon/juniper woodlands, such as we have here, more frequently than any other habitat. They typically first appear here in mid- to late March and begin nest-building in mid- April; eggs appear starting early May; and hatchlings emerge a couple of weeks thereafter. This year, though, activity seemed to start 2-3 weeks later than usual. Speculation by a state entomologist and several fly-fishing aficionados suggested that–due to a long drought, heavy snows the previous winter, and a cold spring (we had a fire in the wood stove on Memorial Day weekend!)–all sorts of spring-related bird and insect activities lagged a bit throughout the state. Here’s an interesting MOBL factoid from Birds of North American Online: Of the 3 bluebird species in the US, MOBLs are the most reliant on insects all year long. Somehow, that makes me feel a bit better that I don’t offer any of the specialized suets that many in other areas do. (Of course, that wouldn’t rule out offering mealworms—but I don’t do that either.) You can find lots of wonderful information about bluebirds at the Sialis Web page.
The males can be a brilliant blue (how dare Sibley refer to it as “a pale blue?”) all over, although the MOBLs in our area are more likely to be a bit less brilliant, with grayer tones. But lovely, nonetheless. Here’s a photo of a typical male for our area, posing against the CO blue sky. (Click on any photo to get a larger version, then use your browser’s “Back” button to return to this page.)
The females are much grayer overall, with blue primarily on their wings and tails. Here’s a female, also posing against the CO blue sky.
This year, we had 6 nesting pairs–a high number for us. And, amazing but true, we had 5 pairs attempt 2nd broods. (I don’t think 2nd broods are necessarily unusual for all MOBLs—just here.) Perhaps the late arrival of early spring insect hatches resulted in a different food supply than would normally have been available at the time of 2nd broods here. Who knows? Only one of the 2nd broods fledged any young, though. Interestingly, that brood was raised by a lone—and exhausted, I would imagine—male. After the 2nd weekly check on the eggs, I never saw the female at the nest box again, although the male always zoomed in to make his presence known. Let’s hear it for dads—and especially single dads—everywhere. I don’t feed supplemental mealworms to our insectivores, since I prefer that they eat the myriad native insects available (as they have evolved to do). As well, I rarely interfere with natural happenings at our nest boxes; offering artificial cavities is all the manipulation we usually do. However, had I had mealworms on hand, I would have helped this dude out in a heartbeat. As it was, though, he fledged 2 youngsters that carry his hardy, tenacious genes.
Okay, enough sentimentality. Here’s a photo of a typical MOBL nest. They construct the most sculptural nests of all of the cavity nesters in our area. I don’t think any of our photos do them justice. The birds have a marvelous way of swirling long strands of juniper bark to form the outer base of the nest. The nest cup is then lined with thinner strips of juniper and whatever meager vegetation they can find in the area. (We have very little understory to speak of, so grasses and such are hard to come by.)
The eggs are classic bluebird—a lovely blue and about 3/4″ long. Here’s a photo of an egg from an abandoned late 2nd brood of 4 eggs. And below that, a clutch of eggs in situ. Clutches here are typically 4 or 5 eggs. Unmistakable as anything but MOBLs: Unless an unusual Western Bluebird pair is nesting (which happened for the first time last year), no other cavity nesters have blue eggs in our area. Interestingly, many of the MOBL nests incorporated a few feathers this year–not something that is typical here. (Books I consulted mentioned that WEBLs on occasion add feathers to their nests—which made me wonder, early on, whether we might have had some WEBL pairs nesting. But I saw no mention of MOBLs doing so.) In the 2nd photo, you can see a Band-tailed Pigeon feather in the lower right, which were very plentiful because we had huge flocks of these behemoths at our feeders this spring and summer. You can also see the sculptural swirls of the nest cup, in this one made up mostly of thin strips of juniper bark.
Next, a photo of nestlings about 2 days old. (Call me crazy, but I think all bird hatchlings look rather like embryonic dinosaurs at this stage. Can you really doubt their ancestry once you’ve gotten good looks at what emerges from the eggs?)
These nestlings are about 4 days old. In addition to several Band-tailed Pigeon feathers at the top, a Northern Flicker (obviously, red-shafted) feather adds a jaunty splash of color.
At last—a photo of nestlings that are actually starting to look like MOBLs. These little fellows are about 9 days old, with pin feathers emerging on their wings while still sporting natal down on their heads. There are at least 3 in that nest, although only 2 are visible from this view.
And in closing, one of my favorite photos of this season. This female had just about had it with our messing with her nest. When we approached the box for photos, she zoomed in and plunked herself down on a branch about 3 feet away from Zell, at eye level. She stayed there while he took a photo of the nestlings. After we had closed the box, she stayed put and Zell snapped this photo. If looks could kill…
© 2008 Tina Mitchell