[cobirds] Re: House Wrens increasing in Denver

Male wrens are notoriously vicious and vigorously defend their territories against other avian intrusion.  They have been known to puncture eggs of other birds and kill nestlings they find in their territory.  This could explain seeing an increase in wrens and a decrease in other species that were unfortunate enough to nest in and be discovered by the resident wrens. I often worry about the Black-capped Chickadees that nest in my boxes ahead of the wrens arriving, being able to fledge their young before the wrens arrive.  When conditions for survival are ideal, populations most likely will see an increase.  So, maybe we've had a perfect storm for wrens, so to speak?  Ample food, nest-sites available for a majority of the birds, maybe a lack of usual predators who may be switching to voles who have also had a banner year?  How about the drought out west?  It is so severe that we could be seeing an irruption of sorts with birds fleeing the extreme conditions there and flocking easterly to our greener pastures because we've had timely rainfall?  Are there more insects?  Who keeps track of that?  Another wren-thought:  HOWR's can have up to three broods in a single season (Stokes) so a good year for wrens can be a REALLY GOOD year for wrens (although the 3rd brood occurs late enough to perish from colder temperatures, so it has to be just right to see that 3rd brood succeed). 

Bob Santangelo
Wheat Ridge

On Tuesday, July 14, 2015 at 4:42:08 PM UTC-6, Robert Righter wrote:

Hi all

The House Wren has always been an infrequent spring and fall migrant in our neighborhood in Denver. Last summer a few House Wrens were noted in our backyard. This summer the House Wren has blanketed not only our backyard but the whole neighborhood's backyards, to where the wren the now is the most common breeding bird species.

It is curious what environmental factors have triggered this increase. We rightfully take note of birds decreasing in populations but rarely take note of bird population increasing, except those that are considered pest species.

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? 

Bob Righter

Denver CO 

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