Please e-mail me if you recognize the white substance or have a suggestion. Perhaps it is a fungus such as powdery mildew? Perhaps the bird is pecking at tiny spider egg sacks that I cannot see? The tree is Cedar Elm (Ulmus crassifolia), the most widespread native elm in Texas. Susan Schaezler discovered the bird earlier in the morning. Strong easterly winds may have forced this particular bird west of its normal migration route. However, a MacGillivray's Warbler was discovered at Warbler Woods the same day!