[CT Birds] Comment on Robins - Part I

Stephen Broker ls.broker at cox.net
Tue Jan 19 15:03:28 EST 2016

On January 9, Jay Kaplan posted on ctbirding a “Comment on Robins”, stating that “it has been hard not to notice the abundance of robins this season” in many areas of the state.  The Hartford CBC, for example, recorded more than 2,500 robins, a record high total for that count.  Jay then posed several questions.  “Did, as we might expect due to the great fruit and berry crop, many of our robins not fly south as usual and remain in Connecticut?  And, what will happen to these birds when winter weather finally arrives – will they migrate southward…or will they perhaps die here due to lack of food?

Greg Hanisek responded (also January 9), “I would tend to think that robins around right now may not include many ‘local’ birds, despite the abundance of fruit.  Our local robins seem to clear out quite early and may not have been affected much by the fruit like crabapples that ripen later.”  Commenting on late summer fruits such as sour cherries, which aren’t persistent, he suggested that later-ripening fruits were now attracting later arriving robins and other fruit-eating birds.  Greg also referred to the nomadic behavior of robins in winter and their tendency to relocate in the state or further south as cold weather comes in and fruit food sources diminish.  Some (many) birds invariably will die in winter.

On January 7, I posted to eBird the following ten minute observation made at my southern Cheshire front yard:  “8:50 A.M., 300 American Robins, steady stream of American Robins flying north, observed from kitchen window.  Flight continues.”  Others have made similar posts to eBird during late December and early January.  The New Haven CBC recorded nearly 1,000 robins on December 19, 2015.  This was by no means a record high count for New Haven, as 6,900 robins were counted on the New Haven Bird Club December 16, 2000 CBC, and 4,600 robins were reported on the NHBC December 19, 2009 CBC.  This year, neither Edwin Way Teale-Trail Wood nor Westport CBCs had particularly high numbers of robins.  Results from other 2015-16 Connecticut CBCs are awaited.

My contributions to the discussion will focus on the diet of American Robins in fall and winter and the nomadic habits of robins during early winter as indicated by Connecticut Christmas Bird Count records over the past century. Diets in bird species are best indicated by stomach contents from birds collected for museums or private cabinets.  The literature on bird stomach contents comes primarily from late 19th century and early 20th century publications, when it was standard practice to shoot a bird in order to see what it ate.  For example, the U.S. Biological Survey and the U.S. Fish and Wildlife Service obtained records for more than 250,000 stomach sample records for some 400 North American bird species.  While that represents a lot of dead birds, this earlier literature continues to be of importance to our understanding of the geographic distribution and seasonality of foraging in birds.

Nathaniel T. Wheelwright published an article, “The Diet of American Robins:  An Analysis of U.S. Biological Survey Records,” in Auk 103:710-725 October 1986.  The article is readily available on-line.  In follow-up posts, I’ll summarize Wheelwright’s conclusions about the diet of American Robins collected in the Northeast and will provide a list of Northeast plants and their fruits based on Wheelwright’s article.  Later (not today), I’ll summarize the information we have on American Robins in Connecticut provided by Christmas Bird Count data.

Steve Broker, Cheshire

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