Monitoring Nocturnal Predators at Eagle Creek Park
by Lina Rifai, Associate Professor at Indiana University Kokomo
Background
Given the significant decline in bird populations over the past 50 years and ongoing rapid urbanization, it has become crucial to gather and analyze data and monitor changes in both resident and migratory bird communities within the remaining green spaces in urban areas. This information allows us to create more effective and targeted conservation strategies.
During migration season, bird watchers who flock to Eagle Creek Park understand its vital role as a stopover (and overwintering) site for many migrating bird species. Northern Saw-whet Owls, weighing about the same as an American Robin, are one such species that use the park as both as stopover site as well as, in some individuals, their wintering grounds.
Why These Owls?
Northern Saw-whet Owls are small, cryptic owls, and little was known about their migratory behavior until Project Owlnet was started. This project was launched in 1994 to understand the timing, intensity, and pace of this owl species’ migration. It promotes cooperation among North American owl-migration researchers and ensures standardized banding protocols. The project has since yielded significant new insights into the migratory patterns of these small owls. Part of the reason that we band this species, therefore, is to continue contributing to this collaborative work, as well as to be able to monitor population trends of such a cryptic and nocturnal species that rarely makes it onto bird counts.
As we know, protecting birds that are migratory requires not only the understanding of their breeding habitat and needs but also of their overwintering and stop-over habitats. And with climate change it becomes even more important to understand what type of habitat these owls can successfully survive and feed in during winter months. As it is one of our smallest owls, it has to be able to avoid detection by predators (mostly larger owls, like Barred Owls), but also be able to not be detected by its own prey when hunting. Therefore, they usually need fairly dense understory cover on wintering grounds, as well as some canopy cover during the day when roosting. With habitat fragmentation, destruction, and climate change it is even more important that we understand how we can effectively protect this owl species.
To gain a better understanding of migrating Northern Saw-whet Owls in Indiana, several researchers across the state follow the banding protocols of Project Owlnet. In previous years naturalist John Schaust, who started the first banding project of these owls at Eagle Creek Park, was able to document that these owls do indeed use the park as a stop-over site. In the fall and winter of 2023, John Schaust and I collaborated to further monitor these small owl migrants
and determine if any individuals would remain in the park after the fall. We captured and banded a total of 16 owls, and later in the season found at least two banded individuals- or recaptures- who had stayed in the park for either an extended period or the entire winter.
Capture and Data Collection
It is crucial to remember that the highest priority in bird research is ensuring the safety of birds. Therefore, all banders are required not only to have the necessary federal and state permits for capturing, banding, and handling these birds but also to have received proper training. Details about banding sites are generally kept confidential to minimize disturbances and human interference in the owls hunting and roosting areas.
To catch owls, we use a combination of mist net setups and audio lures. Once captured, we take several measurements to determine if the owl is male or female—females tend to be larger and heavier than males— and we examine feather mold and wear to assess the age of each individual bird. To be able to age birds, including Northern Saw-whet Owls, we inspect the condition of flight feathers.
Generally, it’s possible to tell if a bird was hatched that year, is in its second year, or is older than one to two years. With Northern Saw-whet Owls, determining age is expedited and more precise due to a pigment in their feathers called porphyrin. When exposed to UV (black) light, these pigments fluoresce a bright pinkish/reddish color. Older feathers contain fewer porphyrin pigments because they degrade over time with sunlight exposure. Thus, under black light, we can quickly determine the age of each flight feather based on its intensity of red/pink fluorescence.
Utilizing this method, we determined the age of the 16 birds caught and banded in 2023— the majority were young birds, either hatched that year or in their second year. In addition to aging and sexing the birds, we also take measurements, such as body fat, keel, etc., that help us gauge the owls body condition during their migration cycle.
Owls generally possess exceptional night vision and require significantly less light than we do to see clearly. Their eyes are so large that there is no space for muscles to attach and move them; however, they compensate for this with the ability to rotate their heads up to 270 degrees in both directions. The eyes of Northern Saw-whet Owls are indeed proportionately so large that the back of their eyeballs is visible through their sizable ear openings.
After we band and measure the owls under artificial lighting, a process that typically takes only a few minutes, it is crucial to let their eyes readjust to the dark. Therefore, we keep them in a dark area for a short period. Once their vision has adapted, we release the owls near wooded and shrubby areas, taking care not to expose their eyes to artificial light during the release.
What’s Next?
The next stage of this project consists of continuing monitoring efforts as well as deploying radio-transmitter tags to monitor individual owls within the park and determine how many of our banded owls will remain for the winter. By the new addition of attached radio-transmitters, we will know for sure which owls will stay, and we won’t have to hope we recapture them later throughout the season to confirm that they stayed all winter. Furthermore, the species’ migratory patterns across North America will be tracked using the MOTUS network once they depart from the park. This initiative is scheduled to start in October 2024.
We’re excited for a successful 2024 season at Eagle Creek Park with one of North America’s smallest, yet fierce birds of prey.
Photo Captions
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A selfie of Lina Rifai and volunteer Grace Whitten with the first owl they caught in 2023, a hatch-year female (photo taken by Lina Rifai )
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Banders checking the nets at 1am (photo taken by Lina Rifai )
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Female hatch-year owl banded at Eagle Creek Park in 2023 (photo taken by Lina Rifai )
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John Schaust holding female second year owl banded at Eagle Creek Park (photo taken by Lina Rifai)
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Northern Saw-whet Owl aging with UV light (photo taken by Jacqueline Eidson)
