Owls are the hardest birds to find. They often roost in dense vegetation or thick pines. Tell-tale signs of owls include, white wash - their excrement (it actually looks like white paint) and pellets (regurgitated organic materials from their prey such as bone and fur).
The most requested bird on the Saturday bird walk at The New York Botanical Garden are owls. They are the hardest bird to find. Owls like to hide and finding them can be like looking for a needle in a haystack.