[cobirds] speculation first-hand on increasing wren numbers

Bob R asks, "Could there could be common environmental reasons for populations both increasing and decreasing? Perhaps knowing the reasons why some birds are increasing could help explain why some birds are decreasing?" 

My own speculation about this is that other folks are doing what we did: In desperation, our effort to rid our yard of House Sparrows (the little foreign killers) was to try to employ the House Wrens as hitbirds--since they were equally good at harassing other birds' nesting attempts.

We put up small swinging houses at critical points around the yard. In short order the first year,  all the houses were occupied with real (as well as a number of dummy) wren nests; and many of those wrens had double-broods! Suddenly the yard was not only guarded, but fiercely defended by small armies of the little critters, driving out just about every intruder. They exploded out of bushes like popcorn whenever we roamed the property. We began to think we might have committed an environmental error.

This year, we limited the wrenhouses to the perimeter corners only; but they used other sites (like the swallow houses) with no problem. While it is true that when wrens have staked out their territory, the House Sparrows rarely venture in for long, we are now having doubts. And somehow two families of Tree Swallows and one of Say's Phoebes, as well as Robins and Bluejays (a problem in other ways) managed to stealth-raise a brood of their own. We have not yet observed any of the barbarous wren behaviors described by others... Perhaps that kind of violence awaits our little yard. Maybe I should put up MORE wren houses, to furnish housing for returnees & their kids and prevent future incidents of violence.

But I shudder to think of the population explosion we are contributing to (sorry about that dangling prep.)

What to do, what to do?

Linda Andes-Georges

central Boulder County