I was intrigued by the discussion of whether in recent years more robins are being seen during winter in the Twin Cities(Charles Neil, Mary White and J. Baumann). I think that I have seen more robins, particularly in large flocks, in recent years. To put this hypothesis to the test I looked at the results from four Christmas Bird Counts over the years that are online at the Minnesota Ornithologists' Union website. The Christmas Bird Counts I checked were Bloomington CBC, St. Paul (North) CBC, Excelsior CBC and the Minneapolis (North) CBC. I found a distinct trend of more robins being counted during the counts since the winter of 1996 than were in prior years. The numbers vary widely each year, but there is a distinct inflection point around 1996 for a larger number of robinssince that date than prior to it. Since 1996, the number ofrobins counted varies greatly from year to year, but I don't see any clear evidence that the numbers are continuing to increase. Average number of robins counted at Twin Cities CBCs: Bloomington St. Paul (North) Minneapolis (North) Excelsior Pre 21.2 17.1 2.5 5.3 1996 1996- 367.4 420.5 114.6 181.2 2017
Median number of robins counted at Twin Cities CBCs: Bloomington St. Paul (North) Minneapolis (North) Excelsior Pre 5 6 0 1 1996 1996- 278 255 26 132 2017 I considered that the increased number of robins might reflect more birders participating in these Christmas counts as well as an increase in birding skills. If there are more skillful birders involved in these counts I would expect a similar increase in the counts of other species. So I looked at the counts reported by the Bloomington CBC for the black-capped chickadee, blue jay and dark-eyed junco. I didn't find any trends or long term changes in the number of these species. Therefore, I'm convinced that the increased number of winter robins is real. I didn't attempt to see if there is a link between the increasein the number of robins counted and weather/climate. That leaves a question in my mind. Are the larger counts just a reflection that the Twin Cities population of robins has increased but the same proportion of that population is overwintering as in the past or have the overwintering habits of the robins changed? The CBC data speaks only to the presence of robins in December. Maybe the only change is when the robins migrate to warmer regions. Maybe if we had many years of counts for January and early February we would find that the number of robins in those months hasn't changed much over the years. As Manley Olson pointed out, once the robins exhaust the availability of crab apples, perhaps they head south and are now just as uncommon in January and February as they were back in the 1950s through 1980s. Val Landwehr Minneapolis ---- Join or Leave mou-net: http://lists.umn.edu/cgi-bin/wa?SUBED1=mou-net Archives: http://lists.umn.edu/archives/mou-net.html
