Monday, March 22, 2021

Nocturnal Duck Commutes: Is a Flying Duck a Sitting Duck?

I think I’ve finally solved a huge mystery that has been bugging me for nearly a year. The very foundation of the scientific world is shaking, and the journal Nature is begging to publish my earthshattering discovery: Lesser Scaup, American Wigeon, and other ducks are commuting in the dark between the Willamette River and Fern Ridge Reservoir twice each day, and their route takes them directly over my house.

Ok, I was being facetious. I know full well that no one in the world cares, and that this is only barely worth blogging. And though my neighbors are nodding in a polite way of wanting to share in my excitement, I actually feel like I’ve cracked the DaVinci code here. Such are the simple pleasures during a year of quarantine.

The whole intrigue actually started well over a year ago, when my next-door neighbors’ son Thomas was visiting between seasonal birding and natural history jobs (yes, I’m envious). He texted me at dusk as he was jogging just a block away and saw a Barred Owl fly right towards our houses. I looked at the text maybe a minute too late but ran outside anyway, and of course I never saw the bird. That sighting, plus Thomas’s having seen a Barred Owl in their yard a few years ago when he was in high school, started my habit of having an evening glass of wine or herbal tea up on the carport roof, hoping to see or even hear an owl as it slowly got dark. I probably gave it up after a few days, but I sporadically continued my vigils over the next several weeks when it wasn’t raining, and in early April a year ago, I saw 11 ducks zip by right at dark, headed west-northwest. Over the next few days I noticed a pattern of this late evening fly-by, and at one point was confident enough only to call one bird an “Aythya sp.”, meaning it was either Lesser Scaup or Ring-necked Duck (both common here), but it was just too fast and and there wasn’t enough light to see details. A few days later I got good views of a pair of Hooded Mergansers making the same fly-by. But until now, “Aythya sp.” has been a dirty mark on my yard list. It has counted as a species, because I had not identified any other member of that genus to species.

Barred Owl from Tillamook County, Oregon. I'm still waiting to add this to my yard list.

This winter I’ve become a more regular fan of sitting out on the back or front deck as it gets dark, still hoping for a Barred Owl. And I noticed that every night, about 20 minutes after official sunset, a total of about 18-35 smallish, fast, diving ducks would fly over in 3-4 small groups. All were headed in exactly the same direction, and it was a nightly thing. The birds I was seeing each dusk were consistent with Lesser Scaup – not tiny like Bufflehead, and not long-billed like mergansers – but I couldn't be sure they weren't Ring-necked Ducks. Finally, one evening I got a longer and better view of the commuting ducks on one of their earlier arrivals, and I was convinced they were Lesser Scaup.

Dusk Vigil from my front deck

At about the same time in mid-January this year, I noticed that a similar number of Lesser Scaup were feeding along a ¼-mile stretch of the Willamette River just over a mile east of me. (It’s awesome to have bike paths along both sides of the river here, with a pedestrian and bike bridge due east of me – one of five such bridges in Eugene, as opposed to just four for cars.)

West Bank Bike Path along the Willamette River in Eugene

I suspected these might be the birds that are flying over my house.

Lesser Scaup on the Willamette River

I used Google Earth to draw a line from where this loose congregation of feeding scaup were to my house, and then extended that line to the next body of water, and bingo – Fern Ridge Dam! For these ducks, this would be a commute of about nine miles.

The flight path commute of Lesser Scaup

On March 1, just before dark, I biked over to the area of the Willamette River where the ducks tend to feed most often, and just a few minutes after I got there, a group of some 20+ Lesser Scaup pattered across the river into flight, zipped downstream as they gained altitude, circled around, flew right over me, and headed in exactly the direction of my house. That’s when I knew I had basically confirmed the identity of the commuting ducks.

The westernmost bend of the Willamette River closest to Fern Ridge Reservoir

One thing I have not done is positioned myself at Fern Ridge Dam to see the ducks arriving. Given that it would probably take them at least seven minutes to get to the dam, it would be too dark to see by the time they got there, and then I’d have a 45-minute bike ride back in the winter dark along busy roads. No thank you. Still, I’d like to know whether they are roosting just above the dam on the reservoir or on Kirk Pond just below the dam.

I’ve also been having my early morning coffee on the back deck well before light, and I can hear the ducks flying back to the Willamette River each morning. But a just like every scientific inquiry that has been answered, more questions are raised.

Why these birds are making this commute only while it’s dark? My guess is that it’s safer. Peregrine Falcon is not a rare bird in this region, and they almost exclusively prey on birds in flight. Once a Peregrine has gained altitude above its target, there is little chance to escape its terrifyingly fast dive, and diving ducks, while built for horizontal speed and efficiency aren’t the most agile of birds in flight. As long as the ducks are on the water, they are safe from Peregrines, but in flight during the day, they are, well, sitting ducks.

Another bonus of my daily sunset vigils has been adding American Wigeon to my yard list. For several nights in a row, at least 10 minutes after the Lesser Scaup, when it’s much darker, I’ve been able to hear a flock of wigeon, and at least twice managed to spot the flock as they commuted in more or less the same direction. I presume these birds forage during the day at Delta Ponds and also move to roost on the reservoir. But this was a phenomenon that begun suddenly at the end of January and ended in early March. Why just then, and not earlier in the winter? Could these have been migrants and not locally wintering wigeon?

I’ve also started wondering how identifiable ducks are solely based on the whistle their wings make. There have been about five Common Goldeneye foraging on the Willamette River alongside the scaup, and I’m almost certain that I’ve heard them in flight when it’s been too dark to even see shapes; they have a very loud wing whistle, and I managed to get one pretty solid recording of them. I’ve determined that the scaup don’t have much of a wing whistle, but how distinctive is Common Goldeneye whistle? How does it differ from Hooded Merganser, or the obvious wing whistle in some dabblers, like Mallard and Wood Duck? Are the spectrograms of the wing whistles of each species diagnostic? My own sound library is lacking recordings of most of these, and while a Cornell compilation has an amazing recording of a Common Goldeneye whistle, it’s of a bird taking off, not one in mid-flight. The primary frequency and first harmonic of my recording match that one well, but it's not strong enough to show the higher harmonics nor the shape of each individual wing beat sound.

Incidentally, I’ve also noticed a pattern to the flight direction to many of the Double-crested Cormorants I see here. While a few seem to be clearly just commuting between the Willamette and Fern Ridge, a majority are off to the NE of my house by a few blocks, quite high, and headed in a NNW direction. I drew a line between the location on the Willamette where I frequently see numbers of them, just downstream from the Greenway Bridge, to the Junction City Fish Pond, which also is the only other place regionally where I see numbers of them. And bullseye – the line I draw between those two places on Google Earth falls exactly on the flight path where I see them. Curiously, this flight is almost exactly the same distance as what the ducks are doing.

Presumed Double-crested Cormorant commute