Of our 6 typical species of cavity nesters, the White-breasted Nuthatch (WBNU) is the most widespread nationally. Colorado is tied for a measly 11th place in WBNU populations, with a meager 2.1% of WBNU population. Three primary populations have been noted, separated by their different calls. I’m only familiar with 2 of those types. The one we have here—the interior west population—uses a rapid series of 2-syllable notes (Sibley denotes it as yidi-yidi-yidi); the Eastern subspecies has a distinctly different “yank, yank.” The interior west birds also have dark gray flanks, compared to lighter flanks among the Eastern birds. In the East, WBNUs seem to prefer deciduous forests. But in CO, they generally prefer conifer areas, selecting especially pinyon/juniper and ponderosa pine habitats almost equally.
WBNUs are the earliest nest-builders here, beginning construction in mid- to late March. However, egg laying typically is delayed until a month or so after the nests have been started. The first Colorado Breeding Bird Atlas shows the earliest nest-building almost a month later than this—probably not a matter of climate change or other environmental changes in the past 20 years, but rather that many atlasers didn’t start serious monitoring until April and so may have missed these earlier construction activities. Also, WBNUs tend to become quiet when nesting (hard as that may be to believe, given their normally noisy presence), making the discovery and examination of their nests even more challenging—unless, of course, you have the luxury of monitoring nest boxes. In fact, one of the most motivating things about participating as atlasers for the 2nd Colorado Breeding Bird Atlas project was our ability to use our nest box monitoring data to advance the knowledge base of all of the pinyon/juniper cavity nesters. You can find out more information about WBNUs at the Sialis Web site.
We began taking photos of the various nesters for the Sialis.org Web site, to add some photos of western-nesting birds. However, this Web site already had a number of excellent photos of WBNU nestlings at various stages. So, once the eggs hatched here, we didn’t take as many photos of the WBNUs nestlings. Unfortunately, we didn’t realize how much fun we’d have taking photos just for ourselves. Yet another project for next summer.
We had 3 pairs of WBNUs nesting—or attempting to nest—this summer. One pair had extraordinarily bad luck, in part because they chose a box that had previously been inhabited by a chipmunk. I think the chipmunk didn’t take kindly to this attempted usurpation. Two clutches of 6 eggs disappeared before hatching. The other WBNU pairs had better success—one raised 2 and one raised 5.
Nest-building began in mid-March; egg-laying, mid-April; hatching, early May. Clutches sizes were 2, 6, and 6 eggs. Nests varied in their construction styles and materials. This one is rather a jumble; I think that the leaves in this nest were a remnant of the previous chipmunk nest-building, since none of the other WBNU nests had leaves.
This one is a more typical WBNU nest, with a layer of bark topped off with lots of animal hair.
Eggs varied in their coloring as well. This nest shows eggs with very little spotting.
This clutch shows a bit more reddish-brown spotting (and a much more jumbled nest), although you may need to look at the larger image to get a hint of this. (Click on the photo once to enlarge it.)
Hidden a bit to the left of center, again in a jumbled nest, are 2 eggs that show even darker spotting. (This may be splitting hairs, given the resolution of these photos. In person, the differences were much clearer.)
Here is the duo of nestlings at age 3 days. In case you can’t guess, this photo and the one above are from the same box (with a free advertising shout-out to the J. Abner plywood manufacturer).
Finally, two views of a group of 8-day-olds, first without the mirror and next, using the mirror. Five nestlings are in that box, although only 3 are visible in these shots.
Although I didn’t have a camera with me, I had the rare opportunity to actually witness the fledging of the duo on a routine monitoring check. I heard both parents in the area, calling loudly and insistently. (If you know WBNUs, you know this sound all too well.) I called the dog in and we sat down to see what might be happening. Within a matter of about 2 minutes, we witnessed first one youngster, then the other, tumble—quite literally, tumble—out of the box, hit the ground, and scurry over to the cover of a scrub oak, seemingly as directed by the vociferous parents. Once the 2nd fledgling had reached the cover of the scrub oak, the parents fell silent. It’s not often I can, with complete confidence, report fledging status to Cornell’s NestWatch!