Background
The northern saw-whet owl, Aegolius acadicus, (NSWO) is the smallest owl species found in Illinois. It breeds in the boreal forests of North America and overwinters in the central and southern regions of the U.S. Little is known about NSWO behavior beyond their breeding grounds, as their minimal vocalization and tendency to roost in dense understory makes detection during their migration and winter periods difficult. A collaborative initiative known as Project Owlnet combines banding data from stations across North America to understand NSWO demographics, migration timing, and migratory connectivity patterns between stations. Despite this, there is minimal data available about their specific demographics, migration stopover durations, or landscape use in Illinois and on the breeding grounds.
Project Methods
In order to fill these knowledge gaps, our lab has been capturing and banding NSWO’s at Kennekuk County Park from mid October to early December since 2020. We open our nets a minimum of 5 hours 1-2 nights each week, using Y-shaped mist net arrays with a call box in the center. The call box repeats the NSWO male territorial ‘toot’ call, which they use on their breeding grounds. Nets have been opened at Allerton Park once weekly during this period as well. Once captured, measurements such as mass, wing chord, and tail length for every owl are taken. Age is determined by looking at molt patterns under UV light. Sex is determined by comparing wing chord and mass measurements. Since 2021, we have attached Motus tags to 20 owls each season. We are able to determine their activity patterns (i.e. what times of day they are most active), fall and spring departure timing, and roughly triangulate their diurnal roosting locations at Kennekuk via 6 automated radio telemetry towers. NSWOs are also hand-tracked periodically to their diurnal roost locations to understand what habitat characteristics they prefer. Furthermore, we are measuring the response of tagged owls to various NSWO vocalizations to better understand why owls are attracted to the ‘toot’ call during the nonbreeding season.
Preliminary Results
Fall 2023
A total of 46 unique NSWO’s were caught at both study sites: 38 at Kennekuk and 9 at Allerton. Four of these owls were foreign recaptures (owls banded at other stations), with 2 being from Michigan, 1 from Minnesota, and one unknown, as the data hasn’t been entered to the BBL yet. Of these owls, 29 were hatch years (HY), 14 were second years (SY), and 3 were after second years (ASY). A Lot of young owls moving through! The bulk of our owls were female (35!), with 3 being male and 8 being unknown. This supports previous hypotheses that a majority of NSWO migrants through Illinois are females.
Summative Data
Since 2020, 177 new owls have been captured and banded at both sites and 16 foreign recaptures. In total, we have banded 86 females, 9 males, and 26 of unknown sex. We banded 125 HY’s, 34 SY’s, 3 TY’s, 1 ATY, 13 ASY’s and 1 AHY. Our net data suggests there is peak migration through Central Illinois in late October/early November. Our activity data suggests they are most active during crepuscular periods. NSWOs most often select cedars and honeysuckle for their diurnal roosting locations, roosting between 6-10 feet, and sometimes up to ~20 feet.
A Unique Undergraduate Experience
This research project has a unique outreach component via its inclusion as part of an undergraduate field course (NRES 285: Owl Migration). Undergraduate students assist in netting and banding operations and learn how data is collected. These students also design a community outreach event, known as ‘Owl Night’, where they create and provide numerous presentations, games, and crafts to teach the public about owls. Community members of all ages and backgrounds are welcome. At Owl Night, members of the public are also given the chance to see a NSWO up-close and observe banding operations if an owl is caught that night. Owl Nights have been held at both Kennekuk County Park, Homer Lake Forest Preserve, and Allerton Park.
Research on the Breeding Grounds in Northern Wisconsin
In collaboration with Carpenter Nature Center, Beaver Creek Reserve, Bayfield County, WIDNR, USFS, Cable Natural History Museum, and countless volunteers (especially Master Bander Kurt Reed) we have begun to study NSWO on the breeding grounds in northern Wisconsin to better understand the following questions:
- What is the mechanism that results in more female captures than male captures at lower latitudes in the winter?
- Do males/females occupy the same breeding territories from one year to the next?
- Are natural cavities a limiting resource for saw-whet owls in areas of managed timber harvests?
Toward that end, we’ve conducted ten mile survey routes in the breeding season to better understand breeding occupancy, captured and tagged NSWO with Motus transmitters, and installed a network of 20 nestboxes in/near recently logged areas. We also collected feather samples from breeding birds to contribute to the Bird Genoscape Project to be better understand how connected populations of these birds are to those in other parts of the range.
