Cook's Petrel vs Pycroft's Petrel

Cook's Petrel and Pycroft's Petrel are closely related species with subtle differences. The most reliable field mark is the underwing pattern: Cook's Petrel typically shows a more contrasting black-and-white underwing, while Pycroft's Petrel has a less distinct pattern. Both species are similar in size and structure, making plumage details crucial for identification.

Underwing pattern: Look for the contrasting black-and-white underwing in Cook's Petrel, which is more distinct than in Pycroft's Petrel.

Cook's Petrel generally has a more contrasting black-and-white underwing pattern compared to Pycroft's Petrel, which shows a less distinct pattern. This difference is subtle but can be crucial for identification.