It's a Gray Area

It's nearing that time when the family takes its annual trek to south-central Oregon for a day of monitoring nesting Great Gray Owls (Strix nebulosa). We've done this every year since about 1993, banding young when there are some, catching adults occasionally. It started out as a research project investigating the demographic relationship between this population, the one to the south (in and around Yosemite), and others in the Blue Mountains of northeast Oregon and in Idaho/Wyoming/Montana. That genetics study led (as I originally suspected) to the realization that these populations have been largely (if not completely) isolated from one another since the last ice age.

At any rate, in anticipation of this year's outing, here are two pics, the first of our son Nathan with an adult nearly as large as he was, and the second (from last year) of Nathan's daughter, Celly, with a nestling.

The Owl and the Duck

Friday morning, my daughter Willow (whose turn it was to feed them) called me to the duck pen, where there was a male Great Horned Owl. It had apparently found its way into the pen during the night, but couldn't find its way back out. (There're only small spaces where the chicken wire 'roof' doesn't align perfectly with the 'walls,' and, anyway, an owl may be able to descend through such a space and yet be unable to climb straight up to get out the same way.) The result was one dead duck (which had already lived a full life and had quit laying eggs awhile ago) and the opportunity to band the local male owl. My granddaughter Celestine helped Willow and me with the banding.

Great Gray Day

Yesterday, my family took our annual daytrip to the Winema National Forest, where we monitor several nests of Great Gray Owls (Strix nebulosa), banding babies when found. This year, 4 of the 7 nests we checked were active, and we banded 3 young (shown above) at the first and 2 at the second.

I didn't have to do any of the climbing this year, and it was Jasper who felt the wrath--and the talons--of the defensive female at the second nest. After we banded them, Nate volunteered to take them back up to the nest, but he was spared any bloodshed or bruises when I caught the big female (below).


The third nest had just a single nestling, too young to band yet. And at the last nest we checked, the female was still incubating her three eggs, one of which was hatching at the time! (see below) It was a great day (no one was carried off by the ubiquitous mosquitos), and we'll long remember this year's trip.

First Owl Nest

I found my first owl nest of the year today. As expected, it was a Great-horned Owl (Bubo virginianus), the species that nests earliest in these parts. The first week of March is late, in fact, for me to be finding my first one. But I've been that busy lately that I haven't had a chance to check some of the likely spots near home, places where GHOWs have nested in years past. The one I found today is at above 6,000 feet of elevation, in an area where winter is still very much in control. The female was sitting tightly on her eggs while snow accumulated on her back.

Owls do not construct their own nests. So when an owl is found to be incubating on a nest of sticks, then that nest was originally constructed by another bird--raven, hawk, or magpie, perhaps--or by a pack rat. The early nesting by these owls often allows them to take over a previous year's Red-tailed Hawk nest (as in this case) before the hawks have returned from wherever they wintered. In my experience, if a pair of Red-tailed Hawks remains on their territory year-round, they generally are able to protect their favorite nest from use by a pair of Great-horned Owls.

At this point in the breeding attempt, I didn't dare approach the nest closely enough to photograph this particular female displaying the faithfulness of a postal employee ("Neither snow nor sleet..."). So instead I've shared below a photo of a different Great-horned Owl fom the same Oregon county and several years ago.

January Wanderlust

About this time every year, I begin to tire of winter and have a hankerin' to migrate south. This feeling stems from a time (nearly two decades ago) when I did just that for three years in a row. I'd leave the northern, snowy climes of the Boise, Idaho area and drive south. By south I mean through Texas, down the Gulf Coast of Mexico, into Belize, and finally into northern Guatemala. There I would spend the first half of the new year, basking in the warmth of the tropical sun and wresting secrets from some of the myriad different creatures that made (and make) that beautiful forest (of Tikal National Park) their permanent home. Below is one such creature, the Keel-billed Toucan (Ramphastos sulfuratus).

Black-and-White Owls

During my peregrinations in Tikal National Park (Guatemala), I was fortunate enough to spend a good deal of time studying a beautiful and little-known species, the Black-and-White Owl (Strix nigrolineata). In fact, my colleagues (Craig Flatten and Normandy Bonilla) and I were the first to document a nest of this species. Each nest (we eventually found four) was an epiphyte (that is, either a bromeliad or orchid) high in a tree, and all nest trees were in or near bajas (the seasonally flooded lowland forests). On those epiphytes, only a single egg was laid, and to my knowledge this remains the only owl species documented to have such a low reproductive effort.

A number of other interesting natural history facts came out of that study. These owls eat lots of insects, especially the large scarab beetles abundant in those forests. But the mammalian component of their diet is almost exclusively bats, and we believe that their large home range size (relative to other owls of their size, and as we determined through radio-telemetry) was required in order to encompass a sufficient number of the fruit trees most attractive to a variety of bats. Another anecdotal observation was that the one pair we observed in three consecutive seasons exhibited astonishing regularity in their nesting--they laid their single egg on the same date (or within a day either way) each of those years.

In the photo above, you can observe the size difference between the male and female. As in most owls, it's the female that is larger. Since in most other families of birds it is the male that is larger (if any size difference exists), the situation in owls (and other birds of prey) is termed "reversed sexual size dimorphism." In this tropical species--and the other one that we studied (and which I'll post about some other time)--this size difference is greater than almost any species from temperate or boreal zones to the north. This finding, in turn, is contrary to the predictions of many of the theories attempting to explain the adaptive advantage of reversed sexual size dimorphism in owls.

Gray Day

The weather was beautiful, actually, for the family's annual trek to the Winema National Forest (in southcentral Oregon) to monitor a sample of Great Gray Owl (Strix nebulosa) territories and nests. Most are artificial platforms (erected to provide nest substrate in lieu of the large broken-top snags that they would normally use).

But raising a brood of young requires more than a nest platform--it requires prey and lots of it. On the Winema, this means wet meadows full of voles and pocket gophers. Alas, the meadows are not wet this year, but dry and largely devoid of small mammals. So, we were skunked on the annual survey, and I doubt whether many of the owls in this local population even attempted nesting this year. Being relatively long-lived birds, great grays can afford to miss a few breeding seasons; but let's hope there's a break in the drought in the next year or two.

Field Trip

Thursday mornings this Spring, our home school has been taking science field trips. This usually means heading east into the Crooked River National Grasslands, where we've been conducting a study (in its 12th year now) of a population of Loggerhead Shrikes (Lanius ludovicianus).

The highlight of this morning's adventure was banding the 5 baby Long-eared Owls (Asio otus) at a single nest. The nest structure itself (mostly dead juniper sticks in a large live juniper) was originally built by a pair of Black-billed Magpies (Pica pica), which only used it once. Long-eared Owls, which (like almost all owls) don't build their own nests, have used it four or five times since, generally producing three or four owlets in spring. This year's small mammal population seems to be better than average.