This is shaping up to be both a good and bad winter for barred owls. It’s a good one for people who want to see them, and the increase in people reporting seeing them is what has prompted me to write this. Unfortunately, it may also be bad for barred owls on a number of fronts, including food availability and increased mortality from car strikes.

The increased frequency of barred owl detections could be happening for a few reasons. First off, there could just be a huge bias in our detections. Maybe there are more people looking or reporting. Birding has become increasingly popular through the pandemic, and who doesn’t love posting about the cool owl they saw!

Second, there may actually be more owls around. After summers of high reproductivity, usually thanks to an abundance of prey (especially gray squirrels), we tend to see more barred owls. These can be local owls doing well, or owls from more northerly populations that are now coming south if their food sources become scarce, similar to the irruptions we see with snowy owls.

Speaking of food availability, that is our third big factor in owl detections. This has been a potentially challenging winter for owls looking for food. They typically like to pluck rodents that live in the subnivean layer, tunneling below the snow’s surface but not under the hard-packed ground. In areas like southern Maine, where we’ve seen very little snow cover this winter, it becomes harder to catch prey, and owls can often be spotted hanging around bird feeders, waiting for rodents to come to fallen seeds, or hunting along roadsides where habitat and litter attract rodents.

It is this behavior – owls hunting near the roads – that I really want to highlight here. Unfortunately, the majority of barred owls that I have seen this winter have been dead on the side of the road, hit by a vehicle. A small rodent is especially easy to pick off when it is crossing over a bare road, making a dangerous spot unfortunately enticing to an owl. A common thought is that many rodents are attracted to roadsides because of litter, which certainly doesn’t help matters. But I think many rodents are there because towns typically keep roadside vegetation mowed, making it a great habitat for them.

Keep an eye out for owls this winter. A couple of things you can do to help: drive a little slower, especially at dusk and at night; be more alert and watch for owls hunting from telephone wires; and don’t litter! Of course, you shouldn’t litter anyway, but if you need another great reason, you could potentially save an owl’s life. If you do find an injured owl, contact a wildlife rehabilitator like Avian Haven or The Center for Wildlife.

NEW CAUSE OF VAGRANCY

A few weeks ago, I wrote about some of the rare birds that have been showing up in Maine this winter. The purpose of that article was to explain how or why those birds managed to be thousands of miles from their intended destination. From European northern lapwings that rode low pressure winds over the north Atlantic, to misoriented migratory hummingbirds, I hit on some of the common causes, but since then some really amazing research into another cause of vagrancy has been published, and I want to share that with you.

A new paper in Nature, by Benjamin Tonelli, Casey Youngflesh, and Morgan Tingley, describes a link found between vagrant birds and geomagnetic disturbances. I should pause for a second to explain that, while we still don’t know exactly how they do it, birds have a magnetic sense. One hypothesis is that some birds can sense magnetic pulses thanks to a collection of magnetite near the beak and nasal cavity. This is like having a built-in compass up your nose! Another hypothesis is that birds have certain photopigments in their eyes that are affected by magnetic fields, essentially allowing them to “see” those fields. Again, these are still being studied, and while the exact way birds sense magnetism is still unknown, there is plenty of evidence that they use these magnetoreceptors as an aid in their long distance migrations.

The question, as it relates to vagrancy then, is what happens when these magnetoreceptors are broken, or something throws them off? That is exactly what the authors of that paper in Nature were looking at. Using a massive dataset from the Bird Banding Lab of more than 2 million records of 152 species, they identified individuals that were caught at unexpected locations. I’ll let any statisticians read the full paper for a better explanation of turning vagrancy into a continuous variable, but with that, the researchers could test for any association with geomagnetic disturbances or solar activity. Remember, the earth produces its own magnetic fields, but the sun’s activity can really distort those. And as you may expect, the researchers found a strong association between vagrancy and geomagnetic disturbances, especially in species that migrate long distances.

It is pretty amazing what we continue to learn about the birds around us. Rare and vagrant birds capture our imaginations, and we are only just beginning to understand some of the causes for their wanderings.

Do you have a nature question for Doug? Email questions to ask@maineaudubon.org and visit maineaudubon.org to learn more about birding, native plants, and programs and events focusing on Maine wildlife and habitat. Doug and other naturalists lead free bird walks on Thursday mornings, 8 to 10 a.m, at the Gilsland Farm Audubon Sanctuary in Falmouth.

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