House Wrens increasing in Denver

[Robert Righter]

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 

[Janis Robinson]

I live in Coal Creek Canyon between Boulder and Golden at 8000 ft. We have a LOT of wrens up here this spring and summer -- they were infrequent before. I put up some nest boxes and had 2 successful batches of fledglings in one of the boxes.

Janis Robinson
Coal Creek Canyon

[meredith]

Just to add some available information to the HOWR issue:

House Wrens are usually the second most commonly caught species at our Chatfield banding station (after Yellow Warblers).  We assume that the vast majority of those we catch are summer residents (rather than migrating through).  What we've observed over the 12 years is that HOWR populations fluctuate.  We've had 3 peaks - 2005, 2009 and 2015.  (Not quite every 5 years, but close.)  In the peak years, we caught twice as many (~80) as we did in the lowest years (<40).  We hit our highest number this year at 83.

I wonder if some of the competition being observed this year is the result of the particularly high number of HOWRs this year, as part of a pattern of fluctuating numbers.

Meredith McBurney

Bander, Chatfield Station

Rocky Mountain Bird Observatory 

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

[Comcast]

We live in the foothills above FoCo @6,000ft. We have more Wrens (by sight or song) in our surrounding area than we have had in our 35+ years of living out here. (Purely anecdotal.) The competition must be fierce.

Since the raid on the nest at our place, the house remains unoccupied. I hope we attract a new couple soon. 

Interesting COBird observations. Thank you all for sharing your expertise.

The Lugers

Across from Horsetooth Mtn. Pk.

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[Paula Hansley]

Could this increase in wrens in the foothills and plains be due to the cool and very rainy May?  It was just cool down here but cold above 8500'. 

We had our first nesting wren in my neighborhood in Louisville in 11 years. 

Wrens were much scarcer on my Indian Peaks bird count this year. The totals will be interesting. 

Paula Hansley

Sent from my iPhone

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[Bob Santangelo]

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:

[Bob Santangelo]

I want to make a correction about what I said regarding the number of broods - I said up to three - they only brood 1-2 times, and add that All About Birds says clutch size can be 3-10 eggs (wow!)

Bob Santangelo
Wheat Ridge / Jefferson County

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