Hi, without pictures or a specimen it is hard to make a positive ID but it sounds like you have Bronze Birch borer, which is relatively common in Portland and the Willamette Valley. BBB is native to eastern Oregon and attacks landscape birches - both native and exotic - in western Oregon cities and towns. Once the damage is apparent, it is often too late to save trees from death.

OSU Extension has a new fact sheet on this insect that explains more on ID and control of this insect.

https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9191.pdf

Thank you for submitting your report to the Hotline.
Wyatt

Wyatt Williams
July 16, 2018, 7:54 a.m.