Ask Mr. Smarty Plants

From the journal article above I found a reference to an earlier article that might be the sort of thing you are looking for.  The article by Robert A. Johnson et al. "Nutritional Values of Wild Fruits and Consumption by Migrant Frugivorous Birds" is in Ecology, Vol. 66, no. 3 (June, 1985), pp. 819-827.    The birds in question are:  Brown Thrasher, Gray Catbird, Gray-cheeked Thrush, American Robin, Hermit Thrush, Veery, Wood Thrush, and Red-eyed Vireo.  In the Appendix of this paper (pp. 826-827) you will find a table that gives:

"Variation in mass and morphology, cation content, and nutrient content of individual fruits collected in central Illinois (except A. rubra in Minnesota)." 

The plant species included are:  Rubus allegheniensis, Arisaema triphyllum, Caulophyllum thalictroides, Prunus serotina, Sambucus canadensis (syn.=S. nigra ssp. canadensis), Cornus racemosa, Smilacina racemosa (syn.=Maianthemum racemosus ssp. racemosum), Polygonatum commutatum (syn.=P. biflorum var. commutatum), Phytolacca americana, Actaea rubra, Parthenocissus quinquefolia, Solanum americanum, Celastrus scandens, Panax quinquefolius, Vitis vulpina, Celtis occidentalis, Lindera benzoin, Menispermum canadense, Smilax hispida (syn.=S. tamnoides), Smilax lasioneura, Euonymus atropurpurea, and Rhus radicans (syn.=Toxicodendron radicans ssp. radicans).

You can find all these plants listed in our Native Plant Database. With the exception of Solanum americanum and Smilax lasioneura, all the above plants occur in Pennsylvania (according to the USDA Plants Database) so they should be appropriate for your talk to the Audubon Society meeting in Gettysburg.

Additionally, I would like to recommend Bringing Nature Home:  How Native Plants Sustain Wildlife in Our Gardens by Douglas Tallamy (2007, Portland, Oregon: Timber Press)—in particular, Chapter 13: What does bird food look like?  This chapter describes the insects that feed on the plants and are then fed on by the birds.  So, the chemical components of the plants are important to the birds, not only as food for the birds, but as nutrition for the insects that make up the major portion of the diet of many birds.