This East Oregonian story says a substantial number of Oregon voters are changing their registration from independent status, and from minor parties, and joining the Democratic Party or the Republican Party. This is because the primaries of those two parties are closed, and only members may vote in them. The Oregon primary, including a presidential primary, is May 17.
In 2008, the sharpest change was in the April report, with some continued decline into May. The April 2016 report has not been issued.
In 2008, from January to May, Pacific Green declined 23.1%, Socialist 18.1%, Other 11.1%, Libertarian 8.0%, Non-Affiliated 7.0%.
In 2016, from January to March, Pacific Green declined 11.4%, Progressive 10.8%, Working Family 5.3%, Libertarian 4.2, Other 3.0%, Non-Affiliated 0.9%.
While the article stressed that it was not the automatically registered who were affiliating, it is likely that they are replacing other Non-Affiliated who are switching.
The Pacific Greens had never fully recovered from the loss in 2008, and it now appears they are shrinking again.
Since January 2008, Other has declined by 38.7%, so it must be relatively hard to register as Other. Is this due to a switch away from paper forms? Americans Elect continues to increase, from 79 in November 2012 to 480 in the latest report.