Hello MSRW readers, welcome back to the account of our spring 2025 owl banding season. This week the ice is gone and the weather has been much kinder to us, though much of Cheboygan has failed to regain power. We caught a total of sixty-one Northern Saw-Whet Owls this week, bring our grand total to one-hundred and fifty-nine. We are so excited to have banded our first hundred birds! In addition to this, we had three notable by-catch species, a Merlin, an American Woodcock, and two Mourning Doves.
As the weather gets warmer, we have started to see (or rather hear) an increase in activity when we close our nets. We have heard Winter Wrens, Song Sparrows, Eastern Phoebe, Sandhill Cranes, Brown Creepers, and Eastern Meadowlark with increasing regularity in the mornings. Not just birds either! Spring peepers began to sing this week, and we see more and more Blue-Spotted Salamanders on net checks. We even made special note of moths, which appeared in decent number all of a sudden on night late this week.
Early this week, on the very first net check of the evening, we walked out to what we initially thought was an owl in our nets, only to find a Merlin. Our first raptor let us know exactly how displeased she was at our interference with her evening activities by screaming at us continuously. This was jarringly different than owls, who will hiss at you, but don’t often vocalize. The Merlin was a beautiful female, and luckily we had both the permits and the correct band size to band her. She had a crop we estimated to be about 40% full, so she was clearly catching prey successfully. We released her on the dunes where we caught her and she flew away reproachfully. It was worth the holes she bit in both my thumbs to see a falcon like her up close!
In the very next net, on the very same check, we caught an American Woodcock! It was caught in the nets we use to catch Long-Eared Owls, which have a larger mesh and higher denier thread than those we use to catch NSWO. The Woodcock’s wings are quite short, so it had both wings fully through the mesh like it was wearing a backpack, but it nevertheless was easy to extract and took off easily upon release.
The only other by-catch of the week were two Mourning Doves, caught on separate days and in different nets. The thing odd about them was that we caught both at two o’clock in the morning, which is a confusing time to find a diurnal species.
Our best night of the week was April 6th; we caught twenty-four Northern Saw-Whet Owls, two of which were foreign recaps! The vast majority of NSWO we catch are female, only a few are unknowns, and even fewer are definitively male. Northern Saw-Whets are a sexually dimorphic species, meaning that there an observable, measurable difference in physiology between the sexes. In some birds, like Northern Cardinals, or in duck species, we can quickly and easily sex the birds by their differences in plumage. In NSWO, the differences are much more subtle. Female Saw-Whets are larger than the males, so to determine in-hand if we have a female or a male, we check the ratio of the wing-chord to the weight. This system of sexing gives us the correct sex about 95% of the time. However, the larger males do overlap in size with the smaller females. In birds with very short wing-chords, around 120 cm, a bird can only determined as male if they are less than 88 grams, and as female if they are as heavy or heavier than 93 grams. This ratio system works up 135 grams for determining males. If we get into the larger wing-chords, around 140 cm, we can only determine if a bird is definitively female, or just an unknown. Any bird that falls in-between the hard cutoffs using this system are labeled as unknowns, although statistically these birds do tend to be male.
After extracting dozens of NSWO, you can start to make an educated guess on their sex by how large or small they feel in-hand, although we would never make official hypothesis in this manner. On our best night, we had twenty females, three unknowns, and one definite male. This allowed us to get a few comparison photos!
As the weather continues to warm and we move into the middle of our season, we are hopeful for the Long-Eared Owls that failed to make an appearance this week. We also have our fingers crossed for some more elusive and unlikely owl species to cross our nets…we will keep you updated either way! Thank you for reading, and we will see you next week.
