Nestbox Study

In natural conditions, breeding of this small owl species is tied to forests containing large trees with cavities, resulting from fungal decay or excavations of large woodpeckers, like the Pileated woodpecker and Northern flicker. Locating nest sites for study is often difficult, as owls often breed in remote locations and at low densities. Although we recognize that owls might behave differently in natural cavities, we chose to conduct a nest box program because boxes provide an efficient and cost effective method to document breeding, examine habitat associations of nesting owls, and provide important demographic data to assess population trends and changes in habitat quality.

Associations between these small owl species and forest cover are still evolving, and there is little information about the scale at which these owls respond to habitat change. Since 2021, we are monitoring a network of 60 nest boxes, placed in various habitat types in north-central Alberta. Some of these boxes were inherited from previous projects and are decayed and in need of replacement. Starting from 2024, we

will replace and modify their deployment to suit our protocols.

We build nest boxes made of rough-cut timber and they are hung on trees at least 150 meters from each other. Nest box height did not seem important in previously published studies, but we try to be consistent, with boxes usually placed between 3 and 5 meters above ground. Currently, the boxes are not evenly distributed on the landscape, but along existing roads and trails to facilitate relatively quick access.

Nest box checks usually start in March and each box is checked at least three times during a breeding season. Occupied boxes are visited more often to gather information on clutch size, hatching, and fledging success. Whenever possible, both adult owls and nestlings are banded, as this will serve to answer questions regarding longevity, dispersal, migration or recruitment. At the end of each nesting season, each box is cleaned and a layer of 10 centimeters of wood shavings are placed in the bottom of the box to offer insulation and prevent egg breakage.

Highlights of our findings so far...

Nest box occupancy rates are highly variable (1-12%), regardless of habitat type
One nest box has been occupied by the same female for two consecutive years (first in 2023, then again in 2024) successfully fledging six, respective five owlets.
Two of the three boxes were occupied at our Lady Flower Gardens site, 430 metres apart. One box fledged five, while the other produced six owlets. One of the young we banded was recovered at Lesser Slave Bird Observatory (85 days later) during fall migration banding, covering 217 km.