I sent this to Bob yesterday, but I'll send it out to the rest of the list as well if it helps. Bob had a great question and others may be wondering the same thing. ************************************************************************ ************************************************ As birds return from over-wintering grounds they're typically pretty hungry and looking for a quick and easy source of food, usually with energy that's easy to get. That's where berries come in. The sugar content of many winter berries increases, and sugar is a very quick source of energy that's easy to absorb and utilize by birds. Some of these berries also have some fat content to them (less than 5%), and fat has even more energy than sugar (there are some physiological and metabolic differences in how fat & sugar are utilized by birds, and not every bird can digest fat). Additionally, berries require very little effort to find and eat compared to foraging for prey, so many birds will preferentially choose berries over other food types if berries are available and/or abundant. As berries dwindle, and invertebrates become more available and abundant in the warmer weather of spring and summer birds will begin to consume them more frequently as well as feed them to their young. Many kinds of earthworms are relatively new to Ohio and areas further north, where they've been introduced as non-native species (see: http://audubonmagazine.org/exotics/exotics0403.html). While robins do eat earthworms, much of their winter diet is typically comprised of fruit (~90%). In spring, March and April, when days are fairly warm to mild but evenings are cooler, robins will eat earthworms and other invertebrates, but still depend on fruit as a source of energy to help them survive the night temperatures. Many thrushes tend to be frugivorous throughout the year, as well as mimic thrushes and a number of other birds. Some birds that we traditionally think of as solely insectivorous, like warblers, will switch to a fruit diet during the fall as they're migrating. Some birds start out eating fruit as nestlings. Northern Mockingbirds, for example, feed fruit to their young while they're still in the nest. During the first few days of an altricial chick's life it is incapable of maintaining its own body temperature, which is why the parents sit on the nest for much of the time. However, about the time the young birds' metabolism kicks in to maintain their own body temperature the Mockingbird parents begin feeding them fruit. The fruit is a source of energy for their metabolism, and the invertebrates are a source of protein and minerals for growing muscles and bones. I hope this helps. Thanks, Casey Casey Tucker Education Specialist Audubon Ohio 692 N. High St., Suite 303 Columbus, OH 43215 614-224-3303 (phone) 614-224-3305 (fax) [log in to unmask] www.audubonohio.org ______________________________________________________________________ Ohio-birds mailing list, a service of the Ohio Ornithological Society. Our thanks to Miami University for hosting this mailing list. Additional discussions can be found in our forums, at www.ohiobirds.org/forum/. You can join or leave the list, or change your options, at: http://listserv.muohio.edu/scripts/wa.exe?LIST=OHIO-BIRDS Send questions or comments about the list to: [log in to unmask]