Cypress trees have roots that grow straight up above the ground, called a ‘knee’. Trap might be a better name since you cannot avoid tripping on them.
Eastern Phoebes use them as perches to look over the waters surface for small insects. Swamps have Cypress Knees, insects, so of course Phoebes love to be here.
When you spot a Phoebe it’s best to focus the camera on the Knee. The bird will almost always return to the perch after each dive for an insect.