Date: 9/2/20 9:49 am
From: Joel Geier <clearwater...>
Subject: [obol] Re: Vultures along Hwy 34
Sorry, a little late to this conversation ...

Grass-seed farmers in the mid-Willamette Valley do frequently spread zinc phosphide pellets as rodenticide when the population of gray-tailed voles spikes.

Here's an advisory that was posted by Oregon Department of Agriculture during 2016. The season for application of zinc phosphide in that year was restricted to late April through August 31st.
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From reading the Capital Press in past outbreaks, the restriction is supposed to be to limit the risk of non-target species (such as wintering waterfowl) directly ingesting the pellets.

I don't see any similar notice for this year on the ODA website, but perhaps someone else can find one by poking around here:
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Secondary poisoning of raptors is a risk that some of us have expressed concern about over the years. The only research that I've been able to find was veterinary research related to pets such as house cats. Indications from that research are that secondary poisoning should occur only if there are undissolved zinc phosphide pellets in the guts of the rodents being ingested.

It's easy to imagine that raptors "waddling from vole to vole" (as Lars expressed it) could scarf up voles that just gobbled up a few zinc phosphide pellets. So I wouldn't dismiss the concern that Mary Holbert raised.

Joel Geier
Camp Adair area north of Corvallis

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