Why are blackbirds leaving poop on our pool cover?

Blackbirds are likely leaving droppings on your pool cover because they are attracted to the area for food or a resting spot. The pool cover may provide a flat surface that is appealing for them to land on. Additionally, if there are insects or seeds nearby, they may be foraging in that vicinity. This behavior is typical for many birds, especially in areas where they find a consistent food source.