During the 1793 Philadelphia yellow fever epidemic, father and son traveled to Cape Henlopen to collect and preserve birds, from August 21 to September 19, 1793.

On June 22, 1796, Charles wrote to Thomas Jefferson: "My third Son having the Talents of preserving the various Subjects of the Animal Kingdom, affords me considerable aid—from which I flatter myself that a reciprocal exchange will be made on our part.

"[6] In a letter to Étienne Geoffroy Saint-Hilaire on April 30, 1797, Charles wrote "...with a Son that now collects and preserves with me, I promise myself to fill my store Boxes with many valuable subjects ready for exchange.

Charles Willson Peale reflected on his son's death in a letter to Palisot de Beauvois, dated June 16, 1799:I am so much affected with the loss of that dear youth that I can scarcely write this for floods of tears.–I snatched him then from death, to take him to New York, and vainly hoped that the affection and attention of a family; (Mrs. Peale's Uncles) would have keept him from New York, in a high, airy & healthy situation where he might recover his flesh & strength, but alass!

I strive to bear up against this affliction, but I have such frequent calls to remember his assifious labours, while persuing my favorite persuits, that the Woods as well as my Study often witness my pangs–and knowing the importance of my labours to put my Museum in a lasting condition, and thereby secure its permanent establishment, I sometimes fear this cankerworm, Grief, will prey on my Vitals, and shorten my days.