Bird mystery drops in on Sisters

About three weeks ago, a Western grebe, Aechmophorus occidentalis ran out of gas during its migratory journey and crashed on a road in the Sisters area.

At the time, most bird enthusiast thought it was a little late for these swan-like fish-eaters to be headed south or west to warmer feeding areas. But last Thursday morning - with the cold snap sending nighttime temperatures plummeting to 19 below zero - another grebe turned up on the snow-covered lawn next to the Sisters Ranger District office.

The appearance of this recent grebe in early morning meant that the grebe had to have been migrating at night in air temperature at least 10 below zero. That would mean the bird, moving through the frigid air going at least 20 MPH (to stay aloft), would have pushed the chill factor down to minus 35 degrees Fahrenheit.

During spring and summer, Western grebes nest in colonies of hundreds on large inland lakes, and sometimes spend winter on marshes along the Oregon Coast, down into California and Mexico; however, by now they should have already passed by on their night migration.

The male and female grebe (and occasionally a rival male) carry out a spectacular courtship display; male and females (and interlopers) will rear up and patter across the water's surface. Photographers of the award-wining Disney nature films put the spotlight on this courtship display years back.

Western grebes gobble up prey by diving into the water and pursuing carp, herring, mollusks, crabs and salamanders, both adult and larval forms.

There are very few places in Sisters that favor prey for grebes, even in summer. On top of that, the recent sub-zero freezing spell put a thin layer of ice on most of our ponds and lakes, making them inhospitable to diving birds.

Our coastal marshes are associated with estuaries, and are also along waterways between the inner coast, making them ideal feeding areas for grebes. The coastal tidal marshes, which are irreplaceable wildlife habitat, are often based on soils consisting of sandy bottoms or bay muds, where small fish can be found in shallow waters. But the rigorous trip from the interior to the coast - at this time of year especially - would be very difficult.

It would have been a great help toward unraveling the mystery if the grebes had been banded with a USGS numbered band; that way we'd have some idea of where they had come from and when, but neither of them were banded.

So, biologists and bird enthusiasts tuck this mystery into the folder with all the other "I Wonder Why" items wildlife biologists have been collecting over the years. Perhaps a student graduating from Sisters High School will go off to college, take wildlife studies and over a cup of coffee with a colleague begin a conversation with, "Oh, by the way..." and come up with the explanation of how grebes (impossible at it sounds) migrate in air temperature with a chill factor of 35 degrees below zero.