Yellow Holly leaves
Evergreen hollies drop their older leaves in spring. The older leaves are found on branches towards inside of tree.
Cannot tell from picture but does look like older, larger leaves. If so, no treatment necessary.
If new growth is affected then it could be iron deficiency better known as chlorosis and treating with sulfur to reduce soil pH would help.
Since it is along the bike path, we have had lots of rain which they prefer, I would monitor and do nothing at present.
Thank you so much! I will keep an eye on the trees. I appreciate your response.