Date: 3/8/17 7:06 pm
From: <Bigrocketman...>
Subject: [obol] Theory About the Role of Predators in Invasive Species Control

It was an interesting suggestion by Frank Kolwicz, that a decline in Eurasian Collared Dove populations might be due to Sharp-shinned and Cooper's Hawks learning to focus on them. They are larger than Mourning Doves, fly more slowly and with less dodging around in their flight-paths. They don't seem nearly as wary or as inclined to instantly flee, at the first hint of danger. And they have a habit of sitting out in the open, on poles. The hawks may have gradually developed an appreciation for the potential they offered and begun seeking out that species.

I have a similar theory about the major decline in opossum and nutria populations in Oregon during the last three decades. You don't see nearly as many of either as you did during the '60s and '70s. I think that a main factor could be that the predators, such as foxes, coyotes, bobcats and cougars, gradually learned what a good and easily-taken food-source they were. They developed abilities, through several generations, about where to find and how to catch them. Another factor of course, is the role motor vehicles play in opossum control. The depletion of ground-nesting birds by the earlier opossums and the awareness of gardeners near watercourses, about the need to fence and protect their crops, also played a part. Fences have to be deeply extended underground, to keep out the burrowing nutria. In some places, they were worse than deer for eating all your vegetables. There's many foxes and coyotes near where I live and an occasional bobcat or cougar. Along streams where I once
saw dozens of nutria, there was only one this year and then, it was also gone.

Steve McDonald

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