[CT Birds] Comment on Robins - Part II
ls.broker at cox.net
Tue Jan 19 15:06:03 EST 2016
The abstract of Nathaniel T. Wheelwright’s article, “The Diet of American Robins: An Analysis of U.S. Biological Survey Records” (Auk 103:710-725 October 1986) summarizes his review of records of stomach contents of Robins collected throughout North America. Most of the following is direct quotes from the article.
Wheelwright states, “Across their entire range, robins ate fruits representing over 50 genera and invertebrates representing over 100 families. The major food classes, consumed in every combination, were soft-bodied invertebrates, hard-bodied invertebrates, and fruits. The same taxa (especially fruits of the family Rosaceae and invertebrates of the orders Coleoptera and Lepidoptera) predominated in robins’ diets, irrespective of habitat or geographical location, which presumably reflects both selective foraging and the availability of these widespread taxa.” So, robins eat beetles, butterflies, and moths in the breeding season, and they switch to plant fruits/berries (especially in the Rose Family) during energetically expensive feather molt and migration.
Additional points from Wheelwright:
· “The proportion of fruit (by volume) in the diet was much higher in the fall and winter (median values >90%) than in the spring (<10%). Summer values were intermediate.
· “The transition from a diet dominated by invertebrates to a diet dominated by fruits occurred over a 1-2 month period.”
· Most common fruit families in the Northeast – Rose Family (genera Prunus and Rubus). Also, members of Dogwood (e.g., Bunchberry), Heath (e.g., Huckleberry, Blueberry), and Cashew (e.g., Poison Ivy) Families.
· “Most fruits eaten by birds that remained at high latitudes during the winter or returned in the spring were fall-ripening species that persist over the winter on plants. Perhaps the best examples are Rhus species [Poison Ivy, etc.] whose fruits are eaten by robins in New York in every month of the year . . .”
· Mid- to late-summer diet of robins: Rose Family members Prunus (Black Cherry, Sour Cherry) and Rubus (Bramble – Blackberry, Dewberry)
· Fall diet: Rose Family Crataegus (Hawthorne)
· Breeding period diet: “cryptic, indigestible, nutritious insect diet”
· Fall/winter diet: “accessible, easily digested, low nutrition fruit diet”
· “Although robins are generalists in one sense, they appear specialized in another sense because they are tied to certain food types.”
The third post (to follow) summarizes the fruit-bearing plants that serve as food for American Robins in fall and winter.
Steve Broker, Cheshire
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