Subject: [Tweeters] Western Screech-owl and Barred Owls
Date: Mar 9 11:56:59 2011
From: vogelfreund at comcast.net - vogelfreund at comcast.net


March 9th '11

This is just adding my two cents worth. I read, years ago, about a study revealing Barred Owls as predators on cavity nesters. The study was conducted in the Midwest, Michigan I think. But it was cited in a book about Ivory-billed Woodpeckers. So that may well be the critical modus operandi of Barred Owls out here in their new range?

Phil Hotlen
Bellingham, WA
-----------------------------------
----- Original Message -----
From: "J. Acker" <owler at sounddsl.com>
To: "TWEETERS" <Tweeters at u.washington.edu>
Sent: Tuesday, March 8, 2011 5:24:59 PM
Subject: [Tweeters] Western Screech-owl and Barred Owls




Let me start by stating that I do not have a science/biology background, but I have been studying the owls on Bainbridge Island in the capacity of a ?citizen scientist? since 1995. My ?surveys? are less than scientific, as I do not follow a set protocol for conducting them.

I do however, posses a data base that shows a shift in owl species populations.



When I first started owling on Bainbridge in 1995, the most common summer time owl was the Western Screech-owl (WESO). I knew of over a dozen pairs on the Island. Barred Owls (BDOW) did not find their way to the Island until 1992, and I did not detect my first until December of 1995 on a survey. My definition of ?survey? was a birding trip out at night with the purpose of locating owls that involved at least three different locations.



In the interim years, the screech owl population has plummeted here, to the point where I can?t find a screech-owl on the 27 square miles that make up this Island. Last year was my first year without recording a WESO on the Island. But I do have at least 24 pairs of BDOW. The human population here has grown from 16,000 to 22,000, and while substantial , should have had a more negative impact on large owls than small. It did not.



A few facts about the species here in the PNW, at least on Bainbridge Island: BDOW lay eggs the first week of March. WESO lay eggs first week of April. This means that BDOW are out of the nest before WESO, and that adult BDOW are looking for a food source for young before the WESO are. BDOW here are bird eaters. Yes, they eat mammals, and are generally opportunists, but I haven?t seen a BDOW nest yet that did not contain bird feathers- particularly crow. I have even found wren feathers in a BDOW nest. Young WESO out of the nest beg for food using a call that attracts parental attention ? also BDOW attention.



I have witnessed a BDOW make a pass (unsuccessful) at and adult WESO. I have also found young WESO feathers in my driveway the morning following warning ?chuck? calls from a pair of WESO when a BDOW arrived.



I propose that the issue is not so much adult predation of WESO by BDOW, but the inability of WESO to reproduce that is bringing the WESO population down. Yes, there are areas in Sequim apparently that still have a healthy WESO reproducing population, but I would suggest that it is merely a matter of time until a BDOW pair moves in that the population crashes. As Stewart pointed out, the best thing going for WESO now are the small parks that can?t support a BDOW and would normally be considered a population drain for most avian species, as these are the areas that WESO can successfully reproduce in, and get the young to adulthood, without BDOW threats.



There have been several emails that infer that Eastern Screech-owls and Barred Owls cohabit the same area in relative peace. I have not seen literature that supports this, though I have not looked for it either. It could be that eastern BDOW have a mammalian diet rather than an avian based one. I grew up in northeast Ohio, and while I can remember Barred Owl around, I never saw or heard an Eastern Screech-owl. BDOW, being the opportunist that they are, eat anything that moves that is smaller than themselves, if it does not appear difficult to catch and kill.



-J. Acker

owler at sounddsl.com

Bainbridge Island, WA








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