Carolina wren

Someone left a comment recently about our having Carolina wrens here in Kansas during the winter. I cannot find the comment and my reply, so this posting will add some information found through the KSBird-L missive for the day.

The marked range shifts seen with global warming suggest that ranges are limited by temperature. Other findings, however, suggest winter survival is directly tied to food availability. We studied Carolina wrens Thryothorus ludovicianus at the northern edge of their range to understand the roles of temperature and food in limiting this species. We established 21 transects over 3 habitats (residential, city park, and rural) with varying degrees of human influence on temperature and food supply. The three habitat types showed variations in wren density, temperature, and feeder presence. While wren densities showed similar seasonal patterns in all habitats, significantly higher densities of birds were observed in the city park and residential habitats. Post-winter densities of Carolina wrens were predicted by the presence of bird feeders, and not by January mean minimum temperatures. Our findings suggest the winter range limits for endotherms is more directly related to food supply, and only indirectly related to temperature. Therefore supplemental feeding and other changes in food supply may modify the range shifts predicted from temperature changes alone.

Job, J. and Bednekoff, P. A. (2011), Wrens on the edge: feeders predict Carolina wren Thryothorus ludovicianus abundance at the northern edge of their range. Journal of Avian Biology, 42: 16–21. doi: 10.1111/j.1600-048X.2010.05242.x

Comments

[joared]

I commented my surprise that you had a wren in the winter. Interesting their migration pattern has more to do with food availability than temperature since the ones with which I was most familiar appeared to be such fragile tiny little creatures.

[Cop Car]

Joared--Thanks for coming by and for refreshing my memory about your comment. I found the study interesting, and it is but one facet of much debate that has raged over my life-time about whether it was a "good" thing to feed birds in winter or not. Some fear that growing dependence upon our handouts might spell doom for some birds if we fail them.