Small but Mighty— The Northern Saw-whet Owl

The Northern Saw-whet Owl is a small owl (a mere eight inches tall) with a streaked chest and a distinctive white V stretching above its eyes—a winsome and (if you’re a little mammal) ferocious owl. With a chunky body, stubby tail, and round tuftless head, its overall shape and size recall an avocado (narrow end down). As with many owls, this nocturnal predator shows a strong preference for small mammals, particularly Peromyscus mice (e.g., deer mouse, California mouse, brush mouse), as their primary food source. The Northern Saw-whet Owl inhabits all of San Diego County’s mountains with coniferous woodlands but is more common on Palomar and Hot Springs mountains than farther south. Indeed, in the coniferous forests on these mountains, it is the most numerous owl species. Far less frequently seen (or heard) than a screech-owl, this is nevertheless the only small tuftless owl likely to be encountered over most of North America.

One year on our mountain property in Colorado, we hosted a pair of these little sprites raising a clutch in one of our larger nest boxes. Here’s how the experience with these surprise visitors unfolded.

 Mid-February

A male Northern Saw-whet Owl began calling every night near our house—a monotonous, unvarying series of whistled single-note toots. (The moniker “saw-whet” arose from this repetitive one-note call, which allegedly sounds like the noise made when manually sharpening a saw on a whetstone. Or so I’ve been told.)  We last heard him in early March. I figured he’d given up and moved on.

 March 15

During a pre-season check of our 100+ nest boxes, I glimpsed a blur of white at one box’s entrance hole. Maybe a chipmunk had dragged something odd into the box. As I approached, I realized a Northern Saw-whet Owl was watching me from the hole. Holy cow! I walked away quickly, needing to learn more about breeding in this species.

 March 24

On this box check, I tapped lightly on the door, paused, and then opened it very slowly. Peering back at me, a saw-whet hunkered down on what looked like nesting material. I quickly took a photo and left. I e-mailed it to a person who monitored mountain owls elsewhere in Colorado for his opinion. He agreed she was probably getting ready to nest. He gave me some pointers about monitoring the box without stressing her unduly.

 March 31

As I approached the box this time, the female popped up to the entrance hole. Present and accounted for. I left her alone.

 April 8

She wasn’t at the entrance hole when I approached the box this time. I tapped lightly on the box—no response. Cracking the box open just a bit, I found her in a prone position with several prey items along the edge of the box. Perhaps she was incubating eggs and the male had been dropping off meals for her.

April 13

At this check, she left the box when I was still more than 30 feet away, flying to a nearby tree. My presence had disturbed her more than I was comfortable with. Keeping my eye on her, I quickly opened the box, counted four eggs (and two freshly delivered deer mice—yum!), and headed out. As I left the area, the female moved to a closer tree, watching/not watching me. I vowed to leave her to incubate in peace.

Northern Saw-whet Owls lay eggs at about two-day intervals. Since the female starts incubating before the entire clutch is laid, the owlets don’t hatch at the same time. (In many bird species, the female starts incubating only after the entire clutch is laid and the chicks usually all hatch on the same day.)Owl eggs hatch in about 30 days; the female stays on the nest pretty much 24/7 until the youngest nestling is feathered and can keep itself warm on its own (“thermoregulation”), approximately 18 days after hatching. I contacted the owl monitor again, who suggested waiting six weeks before checking again. I decided to stay out of the area of the box completely until late May.

I had no idea I had so much self-control.

 May 26

Six weeks had passed. I kept an eye on the nest box entrance hole as I approached the area. I could see a little face peeking out at the edge of the entrance hole. So, at least one nestling and Mom likely not in the box right now. After the owlet moved back to the box floor, I approached. Opening the door slowly, I snapped a photo, closed the box, and left. The photo showed three nestlings and one unhatched egg. I sent the photo to the monitor, who predicted the oldest would likely fledge a day or so after the photo was taken; the other two would follow it shortly. Indeed, by the next week’s box check, all nestlings had fledged.

Northern Saw-whet Owl population—+3.  Nest box monitor geek—grinning from ear to ear!