Guess the species

@birdsandbats Flightless cormorants, like boobies, have the four toes webbed, so clearly it can be discarded. Galapagos penguin can be a reasonable guess, but the feet are different from the duck/gull kind of feet and tracks, they have thick toes with big claws. It's clear like water that it's a gull track, so before replying here, I looked in Google for find the status of Swallow-tailed gull and find that is not endangered at all, so the only option possible was Lava gull that is Vulnerable.

@jayjds2 the most endangered gull is New Zealand gull, Larus bulleri.

@Kakapo Larus bulleri population estimate in the most populous part of their range: approx. 23,500 individuals (source: http://braid.org.nz/wp-content/uploads/2015/05/Black-billed-gull-survey-yr-2-final-report-WMIL.pdf)

Larus fuliginosus population estimate over their range: up to 1200 individuals (Larus fuliginosus (Lava Gull))

Perhaps the terminology I should have used was "rarest."

Probably. Population is not the only factor of danger for a species. Population tendence, grade of human colonization and consequent habitat destruction/fragmentation, generational lenght, grade of adaptation of the species, resistence to diseases, presence of introduced invasive species, etc etc... also plays a role. Larus fuliginosus have less individuals but is endemic to a protected reserve without human disturbance, and their population is increasing. Larus bulleri have strong population decline, nest predation by introduced rats and increase of human disturbance in colonies. Hence lava gull is Vulnerable while black-billed gull is Endangered. If you type "most endangered gull" in Google, several results will point to black billed.