▶️ Northern Saw-whet Owl

[Donkees]

Nov 18, 2021 MORTON ARBORETUM VISITOR CENTER
Northern Saw-whet Owl ( Aegolius acadicus ) feeding on mouse. Old video from Christmas day last year. Northern Saw-whet Owls often keep a prey in their talons for eating during the day at least on a cold days.

[Probatim]

1. Fantastic little murder birds.

I participated in a NSWO banding event last winter.

We arrived about an hour before dark to set up mist nets and an electronic call. The process included - hiking to the site, checking on the nets, going back to sit around a campfire and shoot the breeze for an hour, and repeat until about 2:00 am.

On our first trip, we caught two NSWO. Each was taken back to the "station" to be weighed, aged, sexed, and checked for body fat. After that, one lucky participant got to hold the owl before it was released.

What we learned is that the vast majority of owls captured like this are females. Males seem to be less likely to migrate. And that despite their size, they are pretty ferocious. The lead bander spent the better part of two hours cleaning up the bites and scratches from the second bird. We also learned it's pretty hit or miss to catch these birds. We ended up with three after 5-6 hours sitting out in 30 degree weather - and that was a "good night".

[Donkees]

2. Is the electronic sound a male's call?

It's interesting that females may leave the owlets final care to the male and seek another mate:

At first, adult male brings all food to nest, female feeds it to young. Female remains with chicks until youngest is about 18 days old; then she may begin to hunt for them also, or may depart. Young leave nest at about 4-5 weeks, remain together near nest and are fed (mostly by male) for at least another 4 weeks. Female may sometimes find another mate and nest a second time in one year.

https://www.audubon.org/field-guide/bird/northern-saw-whet-owl

[Probatim]

3. It is indeed a male call - but they say it does not explain the disparity. Here's a helpful link:

https://www.projectowlnet.org/methods/migrant-owl-netting-protocols/

Age/sex class differences. Summarizing six years of data from Pennsylvania, immature (fall HY) owls were found to migrate significantly earlier than adults, which had significantly higher mass and averaged longer periods of stopover than HYs. Most stations report a significant female bias; at three sites in Pennsylvania, saw-whets categorized as male using a mass/wing chord discriminant analysis accounted for only 6 percent of fall captures, while females were 77 percent; the remaining 17 percent could not be assigned to gender. The use of a male advertisement call as an audiolure does not wholly explain this disparity (Duffy and Matheny 1997).

[Donkees]

4. Thanks, that was an interesting read ...

There is evidence that smaller saw-whet owls (presumably male) and recaptures are more likely to be caught farther away from the audiolure ...